1 //! Compiler intrinsics.
3 //! The corresponding definitions are in `compiler/rustc_codegen_llvm/src/intrinsic.rs`.
4 //! The corresponding const implementations are in `compiler/rustc_mir/src/interpret/intrinsics.rs`
8 //! Note: any changes to the constness of intrinsics should be discussed with the language team.
9 //! This includes changes in the stability of the constness.
11 //! In order to make an intrinsic usable at compile-time, one needs to copy the implementation
12 //! from <https://github.com/rust-lang/miri/blob/master/src/shims/intrinsics.rs> to
13 //! `compiler/rustc_mir/src/interpret/intrinsics.rs` and add a
14 //! `#[rustc_const_unstable(feature = "foo", issue = "01234")]` to the intrinsic.
16 //! If an intrinsic is supposed to be used from a `const fn` with a `rustc_const_stable` attribute,
17 //! the intrinsic's attribute must be `rustc_const_stable`, too. Such a change should not be done
18 //! without T-lang consultation, because it bakes a feature into the language that cannot be
19 //! replicated in user code without compiler support.
23 //! The volatile intrinsics provide operations intended to act on I/O
24 //! memory, which are guaranteed to not be reordered by the compiler
25 //! across other volatile intrinsics. See the LLVM documentation on
28 //! [volatile]: https://llvm.org/docs/LangRef.html#volatile-memory-accesses
32 //! The atomic intrinsics provide common atomic operations on machine
33 //! words, with multiple possible memory orderings. They obey the same
34 //! semantics as C++11. See the LLVM documentation on [[atomics]].
36 //! [atomics]: https://llvm.org/docs/Atomics.html
38 //! A quick refresher on memory ordering:
40 //! * Acquire - a barrier for acquiring a lock. Subsequent reads and writes
41 //! take place after the barrier.
42 //! * Release - a barrier for releasing a lock. Preceding reads and writes
43 //! take place before the barrier.
44 //! * Sequentially consistent - sequentially consistent operations are
45 //! guaranteed to happen in order. This is the standard mode for working
46 //! with atomic types and is equivalent to Java's `volatile`.
49 feature = "core_intrinsics",
50 reason = "intrinsics are unlikely to ever be stabilized, instead \
51 they should be used through stabilized interfaces \
52 in the rest of the standard library",
55 #![allow(missing_docs)]
57 use crate::marker::{Destruct, DiscriminantKind};
60 // These imports are used for simplifying intra-doc links
61 #[allow(unused_imports)]
62 #[cfg(all(target_has_atomic = "8", target_has_atomic = "32", target_has_atomic = "ptr"))]
63 use crate::sync::atomic::{self, AtomicBool, AtomicI32, AtomicIsize, AtomicU32, Ordering};
65 #[stable(feature = "drop_in_place", since = "1.8.0")]
67 reason = "no longer an intrinsic - use `ptr::drop_in_place` directly",
71 pub unsafe fn drop_in_place<T: ?Sized>(to_drop: *mut T) {
72 // SAFETY: see `ptr::drop_in_place`
73 unsafe { crate::ptr::drop_in_place(to_drop) }
76 extern "rust-intrinsic" {
77 // N.B., these intrinsics take raw pointers because they mutate aliased
78 // memory, which is not valid for either `&` or `&mut`.
80 /// Stores a value if the current value is the same as the `old` value.
82 /// The stabilized version of this intrinsic is available on the
83 /// [`atomic`] types via the `compare_exchange` method by passing
84 /// [`Ordering::SeqCst`] as both the `success` and `failure` parameters.
85 /// For example, [`AtomicBool::compare_exchange`].
86 pub fn atomic_cxchg<T: Copy>(dst: *mut T, old: T, src: T) -> (T, bool);
87 /// Stores a value if the current value is the same as the `old` value.
89 /// The stabilized version of this intrinsic is available on the
90 /// [`atomic`] types via the `compare_exchange` method by passing
91 /// [`Ordering::Acquire`] as both the `success` and `failure` parameters.
92 /// For example, [`AtomicBool::compare_exchange`].
93 pub fn atomic_cxchg_acq<T: Copy>(dst: *mut T, old: T, src: T) -> (T, bool);
94 /// Stores a value if the current value is the same as the `old` value.
96 /// The stabilized version of this intrinsic is available on the
97 /// [`atomic`] types via the `compare_exchange` method by passing
98 /// [`Ordering::Release`] as the `success` and [`Ordering::Relaxed`] as the
99 /// `failure` parameters. For example, [`AtomicBool::compare_exchange`].
100 pub fn atomic_cxchg_rel<T: Copy>(dst: *mut T, old: T, src: T) -> (T, bool);
101 /// Stores a value if the current value is the same as the `old` value.
103 /// The stabilized version of this intrinsic is available on the
104 /// [`atomic`] types via the `compare_exchange` method by passing
105 /// [`Ordering::AcqRel`] as the `success` and [`Ordering::Acquire`] as the
106 /// `failure` parameters. For example, [`AtomicBool::compare_exchange`].
107 pub fn atomic_cxchg_acqrel<T: Copy>(dst: *mut T, old: T, src: T) -> (T, bool);
108 /// Stores a value if the current value is the same as the `old` value.
110 /// The stabilized version of this intrinsic is available on the
111 /// [`atomic`] types via the `compare_exchange` method by passing
112 /// [`Ordering::Relaxed`] as both the `success` and `failure` parameters.
113 /// For example, [`AtomicBool::compare_exchange`].
114 pub fn atomic_cxchg_relaxed<T: Copy>(dst: *mut T, old: T, src: T) -> (T, bool);
115 /// Stores a value if the current value is the same as the `old` value.
117 /// The stabilized version of this intrinsic is available on the
118 /// [`atomic`] types via the `compare_exchange` method by passing
119 /// [`Ordering::SeqCst`] as the `success` and [`Ordering::Relaxed`] as the
120 /// `failure` parameters. For example, [`AtomicBool::compare_exchange`].
121 pub fn atomic_cxchg_failrelaxed<T: Copy>(dst: *mut T, old: T, src: T) -> (T, bool);
122 /// Stores a value if the current value is the same as the `old` value.
124 /// The stabilized version of this intrinsic is available on the
125 /// [`atomic`] types via the `compare_exchange` method by passing
126 /// [`Ordering::SeqCst`] as the `success` and [`Ordering::Acquire`] as the
127 /// `failure` parameters. For example, [`AtomicBool::compare_exchange`].
128 pub fn atomic_cxchg_failacq<T: Copy>(dst: *mut T, old: T, src: T) -> (T, bool);
129 /// Stores a value if the current value is the same as the `old` value.
131 /// The stabilized version of this intrinsic is available on the
132 /// [`atomic`] types via the `compare_exchange` method by passing
133 /// [`Ordering::Acquire`] as the `success` and [`Ordering::Relaxed`] as the
134 /// `failure` parameters. For example, [`AtomicBool::compare_exchange`].
135 pub fn atomic_cxchg_acq_failrelaxed<T: Copy>(dst: *mut T, old: T, src: T) -> (T, bool);
136 /// Stores a value if the current value is the same as the `old` value.
138 /// The stabilized version of this intrinsic is available on the
139 /// [`atomic`] types via the `compare_exchange` method by passing
140 /// [`Ordering::AcqRel`] as the `success` and [`Ordering::Relaxed`] as the
141 /// `failure` parameters. For example, [`AtomicBool::compare_exchange`].
142 pub fn atomic_cxchg_acqrel_failrelaxed<T: Copy>(dst: *mut T, old: T, src: T) -> (T, bool);
144 /// Stores a value if the current value is the same as the `old` value.
146 /// The stabilized version of this intrinsic is available on the
147 /// [`atomic`] types via the `compare_exchange_weak` method by passing
148 /// [`Ordering::SeqCst`] as both the `success` and `failure` parameters.
149 /// For example, [`AtomicBool::compare_exchange_weak`].
150 pub fn atomic_cxchgweak<T: Copy>(dst: *mut T, old: T, src: T) -> (T, bool);
151 /// Stores a value if the current value is the same as the `old` value.
153 /// The stabilized version of this intrinsic is available on the
154 /// [`atomic`] types via the `compare_exchange_weak` method by passing
155 /// [`Ordering::Acquire`] as both the `success` and `failure` parameters.
156 /// For example, [`AtomicBool::compare_exchange_weak`].
157 pub fn atomic_cxchgweak_acq<T: Copy>(dst: *mut T, old: T, src: T) -> (T, bool);
158 /// Stores a value if the current value is the same as the `old` value.
160 /// The stabilized version of this intrinsic is available on the
161 /// [`atomic`] types via the `compare_exchange_weak` method by passing
162 /// [`Ordering::Release`] as the `success` and [`Ordering::Relaxed`] as the
163 /// `failure` parameters. For example, [`AtomicBool::compare_exchange_weak`].
164 pub fn atomic_cxchgweak_rel<T: Copy>(dst: *mut T, old: T, src: T) -> (T, bool);
165 /// Stores a value if the current value is the same as the `old` value.
167 /// The stabilized version of this intrinsic is available on the
168 /// [`atomic`] types via the `compare_exchange_weak` method by passing
169 /// [`Ordering::AcqRel`] as the `success` and [`Ordering::Acquire`] as the
170 /// `failure` parameters. For example, [`AtomicBool::compare_exchange_weak`].
171 pub fn atomic_cxchgweak_acqrel<T: Copy>(dst: *mut T, old: T, src: T) -> (T, bool);
172 /// Stores a value if the current value is the same as the `old` value.
174 /// The stabilized version of this intrinsic is available on the
175 /// [`atomic`] types via the `compare_exchange_weak` method by passing
176 /// [`Ordering::Relaxed`] as both the `success` and `failure` parameters.
177 /// For example, [`AtomicBool::compare_exchange_weak`].
178 pub fn atomic_cxchgweak_relaxed<T: Copy>(dst: *mut T, old: T, src: T) -> (T, bool);
179 /// Stores a value if the current value is the same as the `old` value.
181 /// The stabilized version of this intrinsic is available on the
182 /// [`atomic`] types via the `compare_exchange_weak` method by passing
183 /// [`Ordering::SeqCst`] as the `success` and [`Ordering::Relaxed`] as the
184 /// `failure` parameters. For example, [`AtomicBool::compare_exchange_weak`].
185 pub fn atomic_cxchgweak_failrelaxed<T: Copy>(dst: *mut T, old: T, src: T) -> (T, bool);
186 /// Stores a value if the current value is the same as the `old` value.
188 /// The stabilized version of this intrinsic is available on the
189 /// [`atomic`] types via the `compare_exchange_weak` method by passing
190 /// [`Ordering::SeqCst`] as the `success` and [`Ordering::Acquire`] as the
191 /// `failure` parameters. For example, [`AtomicBool::compare_exchange_weak`].
192 pub fn atomic_cxchgweak_failacq<T: Copy>(dst: *mut T, old: T, src: T) -> (T, bool);
193 /// Stores a value if the current value is the same as the `old` value.
195 /// The stabilized version of this intrinsic is available on the
196 /// [`atomic`] types via the `compare_exchange_weak` method by passing
197 /// [`Ordering::Acquire`] as the `success` and [`Ordering::Relaxed`] as the
198 /// `failure` parameters. For example, [`AtomicBool::compare_exchange_weak`].
199 pub fn atomic_cxchgweak_acq_failrelaxed<T: Copy>(dst: *mut T, old: T, src: T) -> (T, bool);
200 /// Stores a value if the current value is the same as the `old` value.
202 /// The stabilized version of this intrinsic is available on the
203 /// [`atomic`] types via the `compare_exchange_weak` method by passing
204 /// [`Ordering::AcqRel`] as the `success` and [`Ordering::Relaxed`] as the
205 /// `failure` parameters. For example, [`AtomicBool::compare_exchange_weak`].
206 pub fn atomic_cxchgweak_acqrel_failrelaxed<T: Copy>(dst: *mut T, old: T, src: T) -> (T, bool);
208 /// Loads the current value of the pointer.
210 /// The stabilized version of this intrinsic is available on the
211 /// [`atomic`] types via the `load` method by passing
212 /// [`Ordering::SeqCst`] as the `order`. For example, [`AtomicBool::load`].
213 pub fn atomic_load<T: Copy>(src: *const T) -> T;
214 /// Loads the current value of the pointer.
216 /// The stabilized version of this intrinsic is available on the
217 /// [`atomic`] types via the `load` method by passing
218 /// [`Ordering::Acquire`] as the `order`. For example, [`AtomicBool::load`].
219 pub fn atomic_load_acq<T: Copy>(src: *const T) -> T;
220 /// Loads the current value of the pointer.
222 /// The stabilized version of this intrinsic is available on the
223 /// [`atomic`] types via the `load` method by passing
224 /// [`Ordering::Relaxed`] as the `order`. For example, [`AtomicBool::load`].
225 pub fn atomic_load_relaxed<T: Copy>(src: *const T) -> T;
226 pub fn atomic_load_unordered<T: Copy>(src: *const T) -> T;
228 /// Stores the value at the specified memory location.
230 /// The stabilized version of this intrinsic is available on the
231 /// [`atomic`] types via the `store` method by passing
232 /// [`Ordering::SeqCst`] as the `order`. For example, [`AtomicBool::store`].
233 pub fn atomic_store<T: Copy>(dst: *mut T, val: T);
234 /// Stores the value at the specified memory location.
236 /// The stabilized version of this intrinsic is available on the
237 /// [`atomic`] types via the `store` method by passing
238 /// [`Ordering::Release`] as the `order`. For example, [`AtomicBool::store`].
239 pub fn atomic_store_rel<T: Copy>(dst: *mut T, val: T);
240 /// Stores the value at the specified memory location.
242 /// The stabilized version of this intrinsic is available on the
243 /// [`atomic`] types via the `store` method by passing
244 /// [`Ordering::Relaxed`] as the `order`. For example, [`AtomicBool::store`].
245 pub fn atomic_store_relaxed<T: Copy>(dst: *mut T, val: T);
246 pub fn atomic_store_unordered<T: Copy>(dst: *mut T, val: T);
248 /// Stores the value at the specified memory location, returning the old value.
250 /// The stabilized version of this intrinsic is available on the
251 /// [`atomic`] types via the `swap` method by passing
252 /// [`Ordering::SeqCst`] as the `order`. For example, [`AtomicBool::swap`].
253 pub fn atomic_xchg<T: Copy>(dst: *mut T, src: T) -> T;
254 /// Stores the value at the specified memory location, returning the old value.
256 /// The stabilized version of this intrinsic is available on the
257 /// [`atomic`] types via the `swap` method by passing
258 /// [`Ordering::Acquire`] as the `order`. For example, [`AtomicBool::swap`].
259 pub fn atomic_xchg_acq<T: Copy>(dst: *mut T, src: T) -> T;
260 /// Stores the value at the specified memory location, returning the old value.
262 /// The stabilized version of this intrinsic is available on the
263 /// [`atomic`] types via the `swap` method by passing
264 /// [`Ordering::Release`] as the `order`. For example, [`AtomicBool::swap`].
265 pub fn atomic_xchg_rel<T: Copy>(dst: *mut T, src: T) -> T;
266 /// Stores the value at the specified memory location, returning the old value.
268 /// The stabilized version of this intrinsic is available on the
269 /// [`atomic`] types via the `swap` method by passing
270 /// [`Ordering::AcqRel`] as the `order`. For example, [`AtomicBool::swap`].
271 pub fn atomic_xchg_acqrel<T: Copy>(dst: *mut T, src: T) -> T;
272 /// Stores the value at the specified memory location, returning the old value.
274 /// The stabilized version of this intrinsic is available on the
275 /// [`atomic`] types via the `swap` method by passing
276 /// [`Ordering::Relaxed`] as the `order`. For example, [`AtomicBool::swap`].
277 pub fn atomic_xchg_relaxed<T: Copy>(dst: *mut T, src: T) -> T;
279 /// Adds to the current value, returning the previous value.
281 /// The stabilized version of this intrinsic is available on the
282 /// [`atomic`] types via the `fetch_add` method by passing
283 /// [`Ordering::SeqCst`] as the `order`. For example, [`AtomicIsize::fetch_add`].
284 pub fn atomic_xadd<T: Copy>(dst: *mut T, src: T) -> T;
285 /// Adds to the current value, returning the previous value.
287 /// The stabilized version of this intrinsic is available on the
288 /// [`atomic`] types via the `fetch_add` method by passing
289 /// [`Ordering::Acquire`] as the `order`. For example, [`AtomicIsize::fetch_add`].
290 pub fn atomic_xadd_acq<T: Copy>(dst: *mut T, src: T) -> T;
291 /// Adds to the current value, returning the previous value.
293 /// The stabilized version of this intrinsic is available on the
294 /// [`atomic`] types via the `fetch_add` method by passing
295 /// [`Ordering::Release`] as the `order`. For example, [`AtomicIsize::fetch_add`].
296 pub fn atomic_xadd_rel<T: Copy>(dst: *mut T, src: T) -> T;
297 /// Adds to the current value, returning the previous value.
299 /// The stabilized version of this intrinsic is available on the
300 /// [`atomic`] types via the `fetch_add` method by passing
301 /// [`Ordering::AcqRel`] as the `order`. For example, [`AtomicIsize::fetch_add`].
302 pub fn atomic_xadd_acqrel<T: Copy>(dst: *mut T, src: T) -> T;
303 /// Adds to the current value, returning the previous value.
305 /// The stabilized version of this intrinsic is available on the
306 /// [`atomic`] types via the `fetch_add` method by passing
307 /// [`Ordering::Relaxed`] as the `order`. For example, [`AtomicIsize::fetch_add`].
308 pub fn atomic_xadd_relaxed<T: Copy>(dst: *mut T, src: T) -> T;
310 /// Subtract from the current value, returning the previous value.
312 /// The stabilized version of this intrinsic is available on the
313 /// [`atomic`] types via the `fetch_sub` method by passing
314 /// [`Ordering::SeqCst`] as the `order`. For example, [`AtomicIsize::fetch_sub`].
315 pub fn atomic_xsub<T: Copy>(dst: *mut T, src: T) -> T;
316 /// Subtract from the current value, returning the previous value.
318 /// The stabilized version of this intrinsic is available on the
319 /// [`atomic`] types via the `fetch_sub` method by passing
320 /// [`Ordering::Acquire`] as the `order`. For example, [`AtomicIsize::fetch_sub`].
321 pub fn atomic_xsub_acq<T: Copy>(dst: *mut T, src: T) -> T;
322 /// Subtract from the current value, returning the previous value.
324 /// The stabilized version of this intrinsic is available on the
325 /// [`atomic`] types via the `fetch_sub` method by passing
326 /// [`Ordering::Release`] as the `order`. For example, [`AtomicIsize::fetch_sub`].
327 pub fn atomic_xsub_rel<T: Copy>(dst: *mut T, src: T) -> T;
328 /// Subtract from the current value, returning the previous value.
330 /// The stabilized version of this intrinsic is available on the
331 /// [`atomic`] types via the `fetch_sub` method by passing
332 /// [`Ordering::AcqRel`] as the `order`. For example, [`AtomicIsize::fetch_sub`].
333 pub fn atomic_xsub_acqrel<T: Copy>(dst: *mut T, src: T) -> T;
334 /// Subtract from the current value, returning the previous value.
336 /// The stabilized version of this intrinsic is available on the
337 /// [`atomic`] types via the `fetch_sub` method by passing
338 /// [`Ordering::Relaxed`] as the `order`. For example, [`AtomicIsize::fetch_sub`].
339 pub fn atomic_xsub_relaxed<T: Copy>(dst: *mut T, src: T) -> T;
341 /// Bitwise and with the current value, returning the previous value.
343 /// The stabilized version of this intrinsic is available on the
344 /// [`atomic`] types via the `fetch_and` method by passing
345 /// [`Ordering::SeqCst`] as the `order`. For example, [`AtomicBool::fetch_and`].
346 pub fn atomic_and<T: Copy>(dst: *mut T, src: T) -> T;
347 /// Bitwise and with the current value, returning the previous value.
349 /// The stabilized version of this intrinsic is available on the
350 /// [`atomic`] types via the `fetch_and` method by passing
351 /// [`Ordering::Acquire`] as the `order`. For example, [`AtomicBool::fetch_and`].
352 pub fn atomic_and_acq<T: Copy>(dst: *mut T, src: T) -> T;
353 /// Bitwise and with the current value, returning the previous value.
355 /// The stabilized version of this intrinsic is available on the
356 /// [`atomic`] types via the `fetch_and` method by passing
357 /// [`Ordering::Release`] as the `order`. For example, [`AtomicBool::fetch_and`].
358 pub fn atomic_and_rel<T: Copy>(dst: *mut T, src: T) -> T;
359 /// Bitwise and with the current value, returning the previous value.
361 /// The stabilized version of this intrinsic is available on the
362 /// [`atomic`] types via the `fetch_and` method by passing
363 /// [`Ordering::AcqRel`] as the `order`. For example, [`AtomicBool::fetch_and`].
364 pub fn atomic_and_acqrel<T: Copy>(dst: *mut T, src: T) -> T;
365 /// Bitwise and with the current value, returning the previous value.
367 /// The stabilized version of this intrinsic is available on the
368 /// [`atomic`] types via the `fetch_and` method by passing
369 /// [`Ordering::Relaxed`] as the `order`. For example, [`AtomicBool::fetch_and`].
370 pub fn atomic_and_relaxed<T: Copy>(dst: *mut T, src: T) -> T;
372 /// Bitwise nand with the current value, returning the previous value.
374 /// The stabilized version of this intrinsic is available on the
375 /// [`AtomicBool`] type via the `fetch_nand` method by passing
376 /// [`Ordering::SeqCst`] as the `order`. For example, [`AtomicBool::fetch_nand`].
377 pub fn atomic_nand<T: Copy>(dst: *mut T, src: T) -> T;
378 /// Bitwise nand with the current value, returning the previous value.
380 /// The stabilized version of this intrinsic is available on the
381 /// [`AtomicBool`] type via the `fetch_nand` method by passing
382 /// [`Ordering::Acquire`] as the `order`. For example, [`AtomicBool::fetch_nand`].
383 pub fn atomic_nand_acq<T: Copy>(dst: *mut T, src: T) -> T;
384 /// Bitwise nand with the current value, returning the previous value.
386 /// The stabilized version of this intrinsic is available on the
387 /// [`AtomicBool`] type via the `fetch_nand` method by passing
388 /// [`Ordering::Release`] as the `order`. For example, [`AtomicBool::fetch_nand`].
389 pub fn atomic_nand_rel<T: Copy>(dst: *mut T, src: T) -> T;
390 /// Bitwise nand with the current value, returning the previous value.
392 /// The stabilized version of this intrinsic is available on the
393 /// [`AtomicBool`] type via the `fetch_nand` method by passing
394 /// [`Ordering::AcqRel`] as the `order`. For example, [`AtomicBool::fetch_nand`].
395 pub fn atomic_nand_acqrel<T: Copy>(dst: *mut T, src: T) -> T;
396 /// Bitwise nand with the current value, returning the previous value.
398 /// The stabilized version of this intrinsic is available on the
399 /// [`AtomicBool`] type via the `fetch_nand` method by passing
400 /// [`Ordering::Relaxed`] as the `order`. For example, [`AtomicBool::fetch_nand`].
401 pub fn atomic_nand_relaxed<T: Copy>(dst: *mut T, src: T) -> T;
403 /// Bitwise or with the current value, returning the previous value.
405 /// The stabilized version of this intrinsic is available on the
406 /// [`atomic`] types via the `fetch_or` method by passing
407 /// [`Ordering::SeqCst`] as the `order`. For example, [`AtomicBool::fetch_or`].
408 pub fn atomic_or<T: Copy>(dst: *mut T, src: T) -> T;
409 /// Bitwise or with the current value, returning the previous value.
411 /// The stabilized version of this intrinsic is available on the
412 /// [`atomic`] types via the `fetch_or` method by passing
413 /// [`Ordering::Acquire`] as the `order`. For example, [`AtomicBool::fetch_or`].
414 pub fn atomic_or_acq<T: Copy>(dst: *mut T, src: T) -> T;
415 /// Bitwise or with the current value, returning the previous value.
417 /// The stabilized version of this intrinsic is available on the
418 /// [`atomic`] types via the `fetch_or` method by passing
419 /// [`Ordering::Release`] as the `order`. For example, [`AtomicBool::fetch_or`].
420 pub fn atomic_or_rel<T: Copy>(dst: *mut T, src: T) -> T;
421 /// Bitwise or with the current value, returning the previous value.
423 /// The stabilized version of this intrinsic is available on the
424 /// [`atomic`] types via the `fetch_or` method by passing
425 /// [`Ordering::AcqRel`] as the `order`. For example, [`AtomicBool::fetch_or`].
426 pub fn atomic_or_acqrel<T: Copy>(dst: *mut T, src: T) -> T;
427 /// Bitwise or with the current value, returning the previous value.
429 /// The stabilized version of this intrinsic is available on the
430 /// [`atomic`] types via the `fetch_or` method by passing
431 /// [`Ordering::Relaxed`] as the `order`. For example, [`AtomicBool::fetch_or`].
432 pub fn atomic_or_relaxed<T: Copy>(dst: *mut T, src: T) -> T;
434 /// Bitwise xor with the current value, returning the previous value.
436 /// The stabilized version of this intrinsic is available on the
437 /// [`atomic`] types via the `fetch_xor` method by passing
438 /// [`Ordering::SeqCst`] as the `order`. For example, [`AtomicBool::fetch_xor`].
439 pub fn atomic_xor<T: Copy>(dst: *mut T, src: T) -> T;
440 /// Bitwise xor with the current value, returning the previous value.
442 /// The stabilized version of this intrinsic is available on the
443 /// [`atomic`] types via the `fetch_xor` method by passing
444 /// [`Ordering::Acquire`] as the `order`. For example, [`AtomicBool::fetch_xor`].
445 pub fn atomic_xor_acq<T: Copy>(dst: *mut T, src: T) -> T;
446 /// Bitwise xor with the current value, returning the previous value.
448 /// The stabilized version of this intrinsic is available on the
449 /// [`atomic`] types via the `fetch_xor` method by passing
450 /// [`Ordering::Release`] as the `order`. For example, [`AtomicBool::fetch_xor`].
451 pub fn atomic_xor_rel<T: Copy>(dst: *mut T, src: T) -> T;
452 /// Bitwise xor with the current value, returning the previous value.
454 /// The stabilized version of this intrinsic is available on the
455 /// [`atomic`] types via the `fetch_xor` method by passing
456 /// [`Ordering::AcqRel`] as the `order`. For example, [`AtomicBool::fetch_xor`].
457 pub fn atomic_xor_acqrel<T: Copy>(dst: *mut T, src: T) -> T;
458 /// Bitwise xor with the current value, returning the previous value.
460 /// The stabilized version of this intrinsic is available on the
461 /// [`atomic`] types via the `fetch_xor` method by passing
462 /// [`Ordering::Relaxed`] as the `order`. For example, [`AtomicBool::fetch_xor`].
463 pub fn atomic_xor_relaxed<T: Copy>(dst: *mut T, src: T) -> T;
465 /// Maximum with the current value using a signed comparison.
467 /// The stabilized version of this intrinsic is available on the
468 /// [`atomic`] signed integer types via the `fetch_max` method by passing
469 /// [`Ordering::SeqCst`] as the `order`. For example, [`AtomicI32::fetch_max`].
470 pub fn atomic_max<T: Copy>(dst: *mut T, src: T) -> T;
471 /// Maximum with the current value using a signed comparison.
473 /// The stabilized version of this intrinsic is available on the
474 /// [`atomic`] signed integer types via the `fetch_max` method by passing
475 /// [`Ordering::Acquire`] as the `order`. For example, [`AtomicI32::fetch_max`].
476 pub fn atomic_max_acq<T: Copy>(dst: *mut T, src: T) -> T;
477 /// Maximum with the current value using a signed comparison.
479 /// The stabilized version of this intrinsic is available on the
480 /// [`atomic`] signed integer types via the `fetch_max` method by passing
481 /// [`Ordering::Release`] as the `order`. For example, [`AtomicI32::fetch_max`].
482 pub fn atomic_max_rel<T: Copy>(dst: *mut T, src: T) -> T;
483 /// Maximum with the current value using a signed comparison.
485 /// The stabilized version of this intrinsic is available on the
486 /// [`atomic`] signed integer types via the `fetch_max` method by passing
487 /// [`Ordering::AcqRel`] as the `order`. For example, [`AtomicI32::fetch_max`].
488 pub fn atomic_max_acqrel<T: Copy>(dst: *mut T, src: T) -> T;
489 /// Maximum with the current value.
491 /// The stabilized version of this intrinsic is available on the
492 /// [`atomic`] signed integer types via the `fetch_max` method by passing
493 /// [`Ordering::Relaxed`] as the `order`. For example, [`AtomicI32::fetch_max`].
494 pub fn atomic_max_relaxed<T: Copy>(dst: *mut T, src: T) -> T;
496 /// Minimum with the current value using a signed comparison.
498 /// The stabilized version of this intrinsic is available on the
499 /// [`atomic`] signed integer types via the `fetch_min` method by passing
500 /// [`Ordering::SeqCst`] as the `order`. For example, [`AtomicI32::fetch_min`].
501 pub fn atomic_min<T: Copy>(dst: *mut T, src: T) -> T;
502 /// Minimum with the current value using a signed comparison.
504 /// The stabilized version of this intrinsic is available on the
505 /// [`atomic`] signed integer types via the `fetch_min` method by passing
506 /// [`Ordering::Acquire`] as the `order`. For example, [`AtomicI32::fetch_min`].
507 pub fn atomic_min_acq<T: Copy>(dst: *mut T, src: T) -> T;
508 /// Minimum with the current value using a signed comparison.
510 /// The stabilized version of this intrinsic is available on the
511 /// [`atomic`] signed integer types via the `fetch_min` method by passing
512 /// [`Ordering::Release`] as the `order`. For example, [`AtomicI32::fetch_min`].
513 pub fn atomic_min_rel<T: Copy>(dst: *mut T, src: T) -> T;
514 /// Minimum with the current value using a signed comparison.
516 /// The stabilized version of this intrinsic is available on the
517 /// [`atomic`] signed integer types via the `fetch_min` method by passing
518 /// [`Ordering::AcqRel`] as the `order`. For example, [`AtomicI32::fetch_min`].
519 pub fn atomic_min_acqrel<T: Copy>(dst: *mut T, src: T) -> T;
520 /// Minimum with the current value using a signed comparison.
522 /// The stabilized version of this intrinsic is available on the
523 /// [`atomic`] signed integer types via the `fetch_min` method by passing
524 /// [`Ordering::Relaxed`] as the `order`. For example, [`AtomicI32::fetch_min`].
525 pub fn atomic_min_relaxed<T: Copy>(dst: *mut T, src: T) -> T;
527 /// Minimum with the current value using an unsigned comparison.
529 /// The stabilized version of this intrinsic is available on the
530 /// [`atomic`] unsigned integer types via the `fetch_min` method by passing
531 /// [`Ordering::SeqCst`] as the `order`. For example, [`AtomicU32::fetch_min`].
532 pub fn atomic_umin<T: Copy>(dst: *mut T, src: T) -> T;
533 /// Minimum with the current value using an unsigned comparison.
535 /// The stabilized version of this intrinsic is available on the
536 /// [`atomic`] unsigned integer types via the `fetch_min` method by passing
537 /// [`Ordering::Acquire`] as the `order`. For example, [`AtomicU32::fetch_min`].
538 pub fn atomic_umin_acq<T: Copy>(dst: *mut T, src: T) -> T;
539 /// Minimum with the current value using an unsigned comparison.
541 /// The stabilized version of this intrinsic is available on the
542 /// [`atomic`] unsigned integer types via the `fetch_min` method by passing
543 /// [`Ordering::Release`] as the `order`. For example, [`AtomicU32::fetch_min`].
544 pub fn atomic_umin_rel<T: Copy>(dst: *mut T, src: T) -> T;
545 /// Minimum with the current value using an unsigned comparison.
547 /// The stabilized version of this intrinsic is available on the
548 /// [`atomic`] unsigned integer types via the `fetch_min` method by passing
549 /// [`Ordering::AcqRel`] as the `order`. For example, [`AtomicU32::fetch_min`].
550 pub fn atomic_umin_acqrel<T: Copy>(dst: *mut T, src: T) -> T;
551 /// Minimum with the current value using an unsigned comparison.
553 /// The stabilized version of this intrinsic is available on the
554 /// [`atomic`] unsigned integer types via the `fetch_min` method by passing
555 /// [`Ordering::Relaxed`] as the `order`. For example, [`AtomicU32::fetch_min`].
556 pub fn atomic_umin_relaxed<T: Copy>(dst: *mut T, src: T) -> T;
558 /// Maximum with the current value using an unsigned comparison.
560 /// The stabilized version of this intrinsic is available on the
561 /// [`atomic`] unsigned integer types via the `fetch_max` method by passing
562 /// [`Ordering::SeqCst`] as the `order`. For example, [`AtomicU32::fetch_max`].
563 pub fn atomic_umax<T: Copy>(dst: *mut T, src: T) -> T;
564 /// Maximum with the current value using an unsigned comparison.
566 /// The stabilized version of this intrinsic is available on the
567 /// [`atomic`] unsigned integer types via the `fetch_max` method by passing
568 /// [`Ordering::Acquire`] as the `order`. For example, [`AtomicU32::fetch_max`].
569 pub fn atomic_umax_acq<T: Copy>(dst: *mut T, src: T) -> T;
570 /// Maximum with the current value using an unsigned comparison.
572 /// The stabilized version of this intrinsic is available on the
573 /// [`atomic`] unsigned integer types via the `fetch_max` method by passing
574 /// [`Ordering::Release`] as the `order`. For example, [`AtomicU32::fetch_max`].
575 pub fn atomic_umax_rel<T: Copy>(dst: *mut T, src: T) -> T;
576 /// Maximum with the current value using an unsigned comparison.
578 /// The stabilized version of this intrinsic is available on the
579 /// [`atomic`] unsigned integer types via the `fetch_max` method by passing
580 /// [`Ordering::AcqRel`] as the `order`. For example, [`AtomicU32::fetch_max`].
581 pub fn atomic_umax_acqrel<T: Copy>(dst: *mut T, src: T) -> T;
582 /// Maximum with the current value using an unsigned comparison.
584 /// The stabilized version of this intrinsic is available on the
585 /// [`atomic`] unsigned integer types via the `fetch_max` method by passing
586 /// [`Ordering::Relaxed`] as the `order`. For example, [`AtomicU32::fetch_max`].
587 pub fn atomic_umax_relaxed<T: Copy>(dst: *mut T, src: T) -> T;
589 /// The `prefetch` intrinsic is a hint to the code generator to insert a prefetch instruction
590 /// if supported; otherwise, it is a no-op.
591 /// Prefetches have no effect on the behavior of the program but can change its performance
594 /// The `locality` argument must be a constant integer and is a temporal locality specifier
595 /// ranging from (0) - no locality, to (3) - extremely local keep in cache.
597 /// This intrinsic does not have a stable counterpart.
598 pub fn prefetch_read_data<T>(data: *const T, locality: i32);
599 /// The `prefetch` intrinsic is a hint to the code generator to insert a prefetch instruction
600 /// if supported; otherwise, it is a no-op.
601 /// Prefetches have no effect on the behavior of the program but can change its performance
604 /// The `locality` argument must be a constant integer and is a temporal locality specifier
605 /// ranging from (0) - no locality, to (3) - extremely local keep in cache.
607 /// This intrinsic does not have a stable counterpart.
608 pub fn prefetch_write_data<T>(data: *const T, locality: i32);
609 /// The `prefetch` intrinsic is a hint to the code generator to insert a prefetch instruction
610 /// if supported; otherwise, it is a no-op.
611 /// Prefetches have no effect on the behavior of the program but can change its performance
614 /// The `locality` argument must be a constant integer and is a temporal locality specifier
615 /// ranging from (0) - no locality, to (3) - extremely local keep in cache.
617 /// This intrinsic does not have a stable counterpart.
618 pub fn prefetch_read_instruction<T>(data: *const T, locality: i32);
619 /// The `prefetch` intrinsic is a hint to the code generator to insert a prefetch instruction
620 /// if supported; otherwise, it is a no-op.
621 /// Prefetches have no effect on the behavior of the program but can change its performance
624 /// The `locality` argument must be a constant integer and is a temporal locality specifier
625 /// ranging from (0) - no locality, to (3) - extremely local keep in cache.
627 /// This intrinsic does not have a stable counterpart.
628 pub fn prefetch_write_instruction<T>(data: *const T, locality: i32);
631 extern "rust-intrinsic" {
634 /// The stabilized version of this intrinsic is available in
635 /// [`atomic::fence`] by passing [`Ordering::SeqCst`]
637 pub fn atomic_fence();
640 /// The stabilized version of this intrinsic is available in
641 /// [`atomic::fence`] by passing [`Ordering::Acquire`]
643 pub fn atomic_fence_acq();
646 /// The stabilized version of this intrinsic is available in
647 /// [`atomic::fence`] by passing [`Ordering::Release`]
649 pub fn atomic_fence_rel();
652 /// The stabilized version of this intrinsic is available in
653 /// [`atomic::fence`] by passing [`Ordering::AcqRel`]
655 pub fn atomic_fence_acqrel();
657 /// A compiler-only memory barrier.
659 /// Memory accesses will never be reordered across this barrier by the
660 /// compiler, but no instructions will be emitted for it. This is
661 /// appropriate for operations on the same thread that may be preempted,
662 /// such as when interacting with signal handlers.
664 /// The stabilized version of this intrinsic is available in
665 /// [`atomic::compiler_fence`] by passing [`Ordering::SeqCst`]
667 pub fn atomic_singlethreadfence();
668 /// A compiler-only memory barrier.
670 /// Memory accesses will never be reordered across this barrier by the
671 /// compiler, but no instructions will be emitted for it. This is
672 /// appropriate for operations on the same thread that may be preempted,
673 /// such as when interacting with signal handlers.
675 /// The stabilized version of this intrinsic is available in
676 /// [`atomic::compiler_fence`] by passing [`Ordering::Acquire`]
678 pub fn atomic_singlethreadfence_acq();
679 /// A compiler-only memory barrier.
681 /// Memory accesses will never be reordered across this barrier by the
682 /// compiler, but no instructions will be emitted for it. This is
683 /// appropriate for operations on the same thread that may be preempted,
684 /// such as when interacting with signal handlers.
686 /// The stabilized version of this intrinsic is available in
687 /// [`atomic::compiler_fence`] by passing [`Ordering::Release`]
689 pub fn atomic_singlethreadfence_rel();
690 /// A compiler-only memory barrier.
692 /// Memory accesses will never be reordered across this barrier by the
693 /// compiler, but no instructions will be emitted for it. This is
694 /// appropriate for operations on the same thread that may be preempted,
695 /// such as when interacting with signal handlers.
697 /// The stabilized version of this intrinsic is available in
698 /// [`atomic::compiler_fence`] by passing [`Ordering::AcqRel`]
700 pub fn atomic_singlethreadfence_acqrel();
702 /// Magic intrinsic that derives its meaning from attributes
703 /// attached to the function.
705 /// For example, dataflow uses this to inject static assertions so
706 /// that `rustc_peek(potentially_uninitialized)` would actually
707 /// double-check that dataflow did indeed compute that it is
708 /// uninitialized at that point in the control flow.
710 /// This intrinsic should not be used outside of the compiler.
711 pub fn rustc_peek<T>(_: T) -> T;
713 /// Aborts the execution of the process.
715 /// Note that, unlike most intrinsics, this is safe to call;
716 /// it does not require an `unsafe` block.
717 /// Therefore, implementations must not require the user to uphold
718 /// any safety invariants.
720 /// [`std::process::abort`](../../std/process/fn.abort.html) is to be preferred if possible,
721 /// as its behavior is more user-friendly and more stable.
723 /// The current implementation of `intrinsics::abort` is to invoke an invalid instruction,
724 /// on most platforms.
726 /// process will probably terminate with a signal like `SIGABRT`, `SIGILL`, `SIGTRAP`, `SIGSEGV` or
727 /// `SIGBUS`. The precise behaviour is not guaranteed and not stable.
730 /// Informs the optimizer that this point in the code is not reachable,
731 /// enabling further optimizations.
733 /// N.B., this is very different from the `unreachable!()` macro: Unlike the
734 /// macro, which panics when it is executed, it is *undefined behavior* to
735 /// reach code marked with this function.
737 /// The stabilized version of this intrinsic is [`core::hint::unreachable_unchecked`].
738 #[rustc_const_stable(feature = "const_unreachable_unchecked", since = "1.57.0")]
739 pub fn unreachable() -> !;
741 /// Informs the optimizer that a condition is always true.
742 /// If the condition is false, the behavior is undefined.
744 /// No code is generated for this intrinsic, but the optimizer will try
745 /// to preserve it (and its condition) between passes, which may interfere
746 /// with optimization of surrounding code and reduce performance. It should
747 /// not be used if the invariant can be discovered by the optimizer on its
748 /// own, or if it does not enable any significant optimizations.
750 /// This intrinsic does not have a stable counterpart.
751 #[rustc_const_unstable(feature = "const_assume", issue = "76972")]
752 pub fn assume(b: bool);
754 /// Hints to the compiler that branch condition is likely to be true.
755 /// Returns the value passed to it.
757 /// Any use other than with `if` statements will probably not have an effect.
759 /// Note that, unlike most intrinsics, this is safe to call;
760 /// it does not require an `unsafe` block.
761 /// Therefore, implementations must not require the user to uphold
762 /// any safety invariants.
764 /// This intrinsic does not have a stable counterpart.
765 #[rustc_const_unstable(feature = "const_likely", issue = "none")]
766 pub fn likely(b: bool) -> bool;
768 /// Hints to the compiler that branch condition is likely to be false.
769 /// Returns the value passed to it.
771 /// Any use other than with `if` statements will probably not have an effect.
773 /// Note that, unlike most intrinsics, this is safe to call;
774 /// it does not require an `unsafe` block.
775 /// Therefore, implementations must not require the user to uphold
776 /// any safety invariants.
778 /// This intrinsic does not have a stable counterpart.
779 #[rustc_const_unstable(feature = "const_likely", issue = "none")]
780 pub fn unlikely(b: bool) -> bool;
782 /// Executes a breakpoint trap, for inspection by a debugger.
784 /// This intrinsic does not have a stable counterpart.
787 /// The size of a type in bytes.
789 /// Note that, unlike most intrinsics, this is safe to call;
790 /// it does not require an `unsafe` block.
791 /// Therefore, implementations must not require the user to uphold
792 /// any safety invariants.
794 /// More specifically, this is the offset in bytes between successive
795 /// items of the same type, including alignment padding.
797 /// The stabilized version of this intrinsic is [`core::mem::size_of`].
798 #[rustc_const_stable(feature = "const_size_of", since = "1.40.0")]
799 pub fn size_of<T>() -> usize;
801 /// The minimum alignment of a type.
803 /// Note that, unlike most intrinsics, this is safe to call;
804 /// it does not require an `unsafe` block.
805 /// Therefore, implementations must not require the user to uphold
806 /// any safety invariants.
808 /// The stabilized version of this intrinsic is [`core::mem::align_of`].
809 #[rustc_const_stable(feature = "const_min_align_of", since = "1.40.0")]
810 pub fn min_align_of<T>() -> usize;
811 /// The preferred alignment of a type.
813 /// This intrinsic does not have a stable counterpart.
814 /// It's "tracking issue" is [#91971](https://github.com/rust-lang/rust/issues/91971).
815 #[rustc_const_unstable(feature = "const_pref_align_of", issue = "91971")]
816 pub fn pref_align_of<T>() -> usize;
818 /// The size of the referenced value in bytes.
820 /// The stabilized version of this intrinsic is [`mem::size_of_val`].
821 #[rustc_const_unstable(feature = "const_size_of_val", issue = "46571")]
822 pub fn size_of_val<T: ?Sized>(_: *const T) -> usize;
823 /// The required alignment of the referenced value.
825 /// The stabilized version of this intrinsic is [`core::mem::align_of_val`].
826 #[rustc_const_unstable(feature = "const_align_of_val", issue = "46571")]
827 pub fn min_align_of_val<T: ?Sized>(_: *const T) -> usize;
829 /// Gets a static string slice containing the name of a type.
831 /// Note that, unlike most intrinsics, this is safe to call;
832 /// it does not require an `unsafe` block.
833 /// Therefore, implementations must not require the user to uphold
834 /// any safety invariants.
836 /// The stabilized version of this intrinsic is [`core::any::type_name`].
837 #[rustc_const_unstable(feature = "const_type_name", issue = "63084")]
838 pub fn type_name<T: ?Sized>() -> &'static str;
840 /// Gets an identifier which is globally unique to the specified type. This
841 /// function will return the same value for a type regardless of whichever
842 /// crate it is invoked in.
844 /// Note that, unlike most intrinsics, this is safe to call;
845 /// it does not require an `unsafe` block.
846 /// Therefore, implementations must not require the user to uphold
847 /// any safety invariants.
849 /// The stabilized version of this intrinsic is [`core::any::TypeId::of`].
850 #[rustc_const_unstable(feature = "const_type_id", issue = "77125")]
851 pub fn type_id<T: ?Sized + 'static>() -> u64;
853 /// A guard for unsafe functions that cannot ever be executed if `T` is uninhabited:
854 /// This will statically either panic, or do nothing.
856 /// This intrinsic does not have a stable counterpart.
857 #[rustc_const_stable(feature = "const_assert_type", since = "1.59.0")]
858 pub fn assert_inhabited<T>();
860 /// A guard for unsafe functions that cannot ever be executed if `T` does not permit
861 /// zero-initialization: This will statically either panic, or do nothing.
863 /// This intrinsic does not have a stable counterpart.
864 #[rustc_const_unstable(feature = "const_assert_type2", issue = "none")]
865 pub fn assert_zero_valid<T>();
867 /// A guard for unsafe functions that cannot ever be executed if `T` has invalid
868 /// bit patterns: This will statically either panic, or do nothing.
870 /// This intrinsic does not have a stable counterpart.
871 #[rustc_const_unstable(feature = "const_assert_type2", issue = "none")]
872 pub fn assert_uninit_valid<T>();
874 /// Gets a reference to a static `Location` indicating where it was called.
876 /// Note that, unlike most intrinsics, this is safe to call;
877 /// it does not require an `unsafe` block.
878 /// Therefore, implementations must not require the user to uphold
879 /// any safety invariants.
881 /// Consider using [`core::panic::Location::caller`] instead.
882 #[rustc_const_unstable(feature = "const_caller_location", issue = "76156")]
883 pub fn caller_location() -> &'static crate::panic::Location<'static>;
885 /// Moves a value out of scope without running drop glue.
887 /// This exists solely for [`mem::forget_unsized`]; normal `forget` uses
888 /// `ManuallyDrop` instead.
890 /// Note that, unlike most intrinsics, this is safe to call;
891 /// it does not require an `unsafe` block.
892 /// Therefore, implementations must not require the user to uphold
893 /// any safety invariants.
894 #[rustc_const_unstable(feature = "const_intrinsic_forget", issue = "none")]
895 pub fn forget<T: ?Sized>(_: T);
897 /// Reinterprets the bits of a value of one type as another type.
899 /// Both types must have the same size. Neither the original, nor the result,
900 /// may be an [invalid value](../../nomicon/what-unsafe-does.html).
902 /// `transmute` is semantically equivalent to a bitwise move of one type
903 /// into another. It copies the bits from the source value into the
904 /// destination value, then forgets the original. It's equivalent to C's
905 /// `memcpy` under the hood, just like `transmute_copy`.
907 /// Because `transmute` is a by-value operation, alignment of the *transmuted values
908 /// themselves* is not a concern. As with any other function, the compiler already ensures
909 /// both `T` and `U` are properly aligned. However, when transmuting values that *point
910 /// elsewhere* (such as pointers, references, boxes…), the caller has to ensure proper
911 /// alignment of the pointed-to values.
913 /// `transmute` is **incredibly** unsafe. There are a vast number of ways to
914 /// cause [undefined behavior][ub] with this function. `transmute` should be
915 /// the absolute last resort.
917 /// Transmuting pointers to integers in a `const` context is [undefined behavior][ub].
918 /// Any attempt to use the resulting value for integer operations will abort const-evaluation.
920 /// The [nomicon](../../nomicon/transmutes.html) has additional
923 /// [ub]: ../../reference/behavior-considered-undefined.html
927 /// There are a few things that `transmute` is really useful for.
929 /// Turning a pointer into a function pointer. This is *not* portable to
930 /// machines where function pointers and data pointers have different sizes.
933 /// fn foo() -> i32 {
936 /// let pointer = foo as *const ();
937 /// let function = unsafe {
938 /// std::mem::transmute::<*const (), fn() -> i32>(pointer)
940 /// assert_eq!(function(), 0);
943 /// Extending a lifetime, or shortening an invariant lifetime. This is
944 /// advanced, very unsafe Rust!
947 /// struct R<'a>(&'a i32);
948 /// unsafe fn extend_lifetime<'b>(r: R<'b>) -> R<'static> {
949 /// std::mem::transmute::<R<'b>, R<'static>>(r)
952 /// unsafe fn shorten_invariant_lifetime<'b, 'c>(r: &'b mut R<'static>)
953 /// -> &'b mut R<'c> {
954 /// std::mem::transmute::<&'b mut R<'static>, &'b mut R<'c>>(r)
960 /// Don't despair: many uses of `transmute` can be achieved through other means.
961 /// Below are common applications of `transmute` which can be replaced with safer
964 /// Turning raw bytes (`&[u8]`) into `u32`, `f64`, etc.:
967 /// let raw_bytes = [0x78, 0x56, 0x34, 0x12];
969 /// let num = unsafe {
970 /// std::mem::transmute::<[u8; 4], u32>(raw_bytes)
973 /// // use `u32::from_ne_bytes` instead
974 /// let num = u32::from_ne_bytes(raw_bytes);
975 /// // or use `u32::from_le_bytes` or `u32::from_be_bytes` to specify the endianness
976 /// let num = u32::from_le_bytes(raw_bytes);
977 /// assert_eq!(num, 0x12345678);
978 /// let num = u32::from_be_bytes(raw_bytes);
979 /// assert_eq!(num, 0x78563412);
982 /// Turning a pointer into a `usize`:
986 /// let ptr_num_transmute = unsafe {
987 /// std::mem::transmute::<&i32, usize>(ptr)
990 /// // Use an `as` cast instead
991 /// let ptr_num_cast = ptr as *const i32 as usize;
994 /// Note that using `transmute` to turn a pointer to a `usize` is (as noted above) [undefined
995 /// behavior][ub] in `const` contexts. Also outside of consts, this operation might not behave
996 /// as expected -- this is touching on many unspecified aspects of the Rust memory model.
997 /// Depending on what the code is doing, the following alternatives are preferrable to
998 /// pointer-to-integer transmutation:
999 /// - If the code just wants to store data of arbitrary type in some buffer and needs to pick a
1000 /// type for that buffer, it can use [`MaybeUninit`][mem::MaybeUninit].
1001 /// - If the code actually wants to work on the address the pointer points to, it can use `as`
1002 /// casts or [`ptr.addr()`][pointer::addr].
1004 /// Turning a `*mut T` into an `&mut T`:
1007 /// let ptr: *mut i32 = &mut 0;
1008 /// let ref_transmuted = unsafe {
1009 /// std::mem::transmute::<*mut i32, &mut i32>(ptr)
1012 /// // Use a reborrow instead
1013 /// let ref_casted = unsafe { &mut *ptr };
1016 /// Turning an `&mut T` into an `&mut U`:
1019 /// let ptr = &mut 0;
1020 /// let val_transmuted = unsafe {
1021 /// std::mem::transmute::<&mut i32, &mut u32>(ptr)
1024 /// // Now, put together `as` and reborrowing - note the chaining of `as`
1025 /// // `as` is not transitive
1026 /// let val_casts = unsafe { &mut *(ptr as *mut i32 as *mut u32) };
1029 /// Turning an `&str` into a `&[u8]`:
1032 /// // this is not a good way to do this.
1033 /// let slice = unsafe { std::mem::transmute::<&str, &[u8]>("Rust") };
1034 /// assert_eq!(slice, &[82, 117, 115, 116]);
1036 /// // You could use `str::as_bytes`
1037 /// let slice = "Rust".as_bytes();
1038 /// assert_eq!(slice, &[82, 117, 115, 116]);
1040 /// // Or, just use a byte string, if you have control over the string
1042 /// assert_eq!(b"Rust", &[82, 117, 115, 116]);
1045 /// Turning a `Vec<&T>` into a `Vec<Option<&T>>`.
1047 /// To transmute the inner type of the contents of a container, you must make sure to not
1048 /// violate any of the container's invariants. For `Vec`, this means that both the size
1049 /// *and alignment* of the inner types have to match. Other containers might rely on the
1050 /// size of the type, alignment, or even the `TypeId`, in which case transmuting wouldn't
1051 /// be possible at all without violating the container invariants.
1054 /// let store = [0, 1, 2, 3];
1055 /// let v_orig = store.iter().collect::<Vec<&i32>>();
1057 /// // clone the vector as we will reuse them later
1058 /// let v_clone = v_orig.clone();
1060 /// // Using transmute: this relies on the unspecified data layout of `Vec`, which is a
1061 /// // bad idea and could cause Undefined Behavior.
1062 /// // However, it is no-copy.
1063 /// let v_transmuted = unsafe {
1064 /// std::mem::transmute::<Vec<&i32>, Vec<Option<&i32>>>(v_clone)
1067 /// let v_clone = v_orig.clone();
1069 /// // This is the suggested, safe way.
1070 /// // It does copy the entire vector, though, into a new array.
1071 /// let v_collected = v_clone.into_iter()
1073 /// .collect::<Vec<Option<&i32>>>();
1075 /// let v_clone = v_orig.clone();
1077 /// // This is the proper no-copy, unsafe way of "transmuting" a `Vec`, without relying on the
1078 /// // data layout. Instead of literally calling `transmute`, we perform a pointer cast, but
1079 /// // in terms of converting the original inner type (`&i32`) to the new one (`Option<&i32>`),
1080 /// // this has all the same caveats. Besides the information provided above, also consult the
1081 /// // [`from_raw_parts`] documentation.
1082 /// let v_from_raw = unsafe {
1083 // FIXME Update this when vec_into_raw_parts is stabilized
1084 /// // Ensure the original vector is not dropped.
1085 /// let mut v_clone = std::mem::ManuallyDrop::new(v_clone);
1086 /// Vec::from_raw_parts(v_clone.as_mut_ptr() as *mut Option<&i32>,
1088 /// v_clone.capacity())
1092 /// [`from_raw_parts`]: ../../std/vec/struct.Vec.html#method.from_raw_parts
1094 /// Implementing `split_at_mut`:
1097 /// use std::{slice, mem};
1099 /// // There are multiple ways to do this, and there are multiple problems
1100 /// // with the following (transmute) way.
1101 /// fn split_at_mut_transmute<T>(slice: &mut [T], mid: usize)
1102 /// -> (&mut [T], &mut [T]) {
1103 /// let len = slice.len();
1104 /// assert!(mid <= len);
1106 /// let slice2 = mem::transmute::<&mut [T], &mut [T]>(slice);
1107 /// // first: transmute is not type safe; all it checks is that T and
1108 /// // U are of the same size. Second, right here, you have two
1109 /// // mutable references pointing to the same memory.
1110 /// (&mut slice[0..mid], &mut slice2[mid..len])
1114 /// // This gets rid of the type safety problems; `&mut *` will *only* give
1115 /// // you an `&mut T` from an `&mut T` or `*mut T`.
1116 /// fn split_at_mut_casts<T>(slice: &mut [T], mid: usize)
1117 /// -> (&mut [T], &mut [T]) {
1118 /// let len = slice.len();
1119 /// assert!(mid <= len);
1121 /// let slice2 = &mut *(slice as *mut [T]);
1122 /// // however, you still have two mutable references pointing to
1123 /// // the same memory.
1124 /// (&mut slice[0..mid], &mut slice2[mid..len])
1128 /// // This is how the standard library does it. This is the best method, if
1129 /// // you need to do something like this
1130 /// fn split_at_stdlib<T>(slice: &mut [T], mid: usize)
1131 /// -> (&mut [T], &mut [T]) {
1132 /// let len = slice.len();
1133 /// assert!(mid <= len);
1135 /// let ptr = slice.as_mut_ptr();
1136 /// // This now has three mutable references pointing at the same
1137 /// // memory. `slice`, the rvalue ret.0, and the rvalue ret.1.
1138 /// // `slice` is never used after `let ptr = ...`, and so one can
1139 /// // treat it as "dead", and therefore, you only have two real
1140 /// // mutable slices.
1141 /// (slice::from_raw_parts_mut(ptr, mid),
1142 /// slice::from_raw_parts_mut(ptr.add(mid), len - mid))
1146 #[stable(feature = "rust1", since = "1.0.0")]
1147 #[rustc_const_stable(feature = "const_transmute", since = "1.46.0")]
1148 #[rustc_diagnostic_item = "transmute"]
1149 pub fn transmute<T, U>(e: T) -> U;
1151 /// Returns `true` if the actual type given as `T` requires drop
1152 /// glue; returns `false` if the actual type provided for `T`
1153 /// implements `Copy`.
1155 /// If the actual type neither requires drop glue nor implements
1156 /// `Copy`, then the return value of this function is unspecified.
1158 /// Note that, unlike most intrinsics, this is safe to call;
1159 /// it does not require an `unsafe` block.
1160 /// Therefore, implementations must not require the user to uphold
1161 /// any safety invariants.
1163 /// The stabilized version of this intrinsic is [`mem::needs_drop`](crate::mem::needs_drop).
1164 #[rustc_const_stable(feature = "const_needs_drop", since = "1.40.0")]
1165 pub fn needs_drop<T>() -> bool;
1167 /// Calculates the offset from a pointer.
1169 /// This is implemented as an intrinsic to avoid converting to and from an
1170 /// integer, since the conversion would throw away aliasing information.
1174 /// Both the starting and resulting pointer must be either in bounds or one
1175 /// byte past the end of an allocated object. If either pointer is out of
1176 /// bounds or arithmetic overflow occurs then any further use of the
1177 /// returned value will result in undefined behavior.
1179 /// The stabilized version of this intrinsic is [`pointer::offset`].
1180 #[must_use = "returns a new pointer rather than modifying its argument"]
1181 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
1182 pub fn offset<T>(dst: *const T, offset: isize) -> *const T;
1184 /// Calculates the offset from a pointer, potentially wrapping.
1186 /// This is implemented as an intrinsic to avoid converting to and from an
1187 /// integer, since the conversion inhibits certain optimizations.
1191 /// Unlike the `offset` intrinsic, this intrinsic does not restrict the
1192 /// resulting pointer to point into or one byte past the end of an allocated
1193 /// object, and it wraps with two's complement arithmetic. The resulting
1194 /// value is not necessarily valid to be used to actually access memory.
1196 /// The stabilized version of this intrinsic is [`pointer::wrapping_offset`].
1197 #[must_use = "returns a new pointer rather than modifying its argument"]
1198 #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
1199 pub fn arith_offset<T>(dst: *const T, offset: isize) -> *const T;
1201 /// Equivalent to the appropriate `llvm.memcpy.p0i8.0i8.*` intrinsic, with
1202 /// a size of `count` * `size_of::<T>()` and an alignment of
1203 /// `min_align_of::<T>()`
1205 /// The volatile parameter is set to `true`, so it will not be optimized out
1206 /// unless size is equal to zero.
1208 /// This intrinsic does not have a stable counterpart.
1209 pub fn volatile_copy_nonoverlapping_memory<T>(dst: *mut T, src: *const T, count: usize);
1210 /// Equivalent to the appropriate `llvm.memmove.p0i8.0i8.*` intrinsic, with
1211 /// a size of `count * size_of::<T>()` and an alignment of
1212 /// `min_align_of::<T>()`
1214 /// The volatile parameter is set to `true`, so it will not be optimized out
1215 /// unless size is equal to zero.
1217 /// This intrinsic does not have a stable counterpart.
1218 pub fn volatile_copy_memory<T>(dst: *mut T, src: *const T, count: usize);
1219 /// Equivalent to the appropriate `llvm.memset.p0i8.*` intrinsic, with a
1220 /// size of `count * size_of::<T>()` and an alignment of
1221 /// `min_align_of::<T>()`.
1223 /// The volatile parameter is set to `true`, so it will not be optimized out
1224 /// unless size is equal to zero.
1226 /// This intrinsic does not have a stable counterpart.
1227 pub fn volatile_set_memory<T>(dst: *mut T, val: u8, count: usize);
1229 /// Performs a volatile load from the `src` pointer.
1231 /// The stabilized version of this intrinsic is [`core::ptr::read_volatile`].
1232 pub fn volatile_load<T>(src: *const T) -> T;
1233 /// Performs a volatile store to the `dst` pointer.
1235 /// The stabilized version of this intrinsic is [`core::ptr::write_volatile`].
1236 pub fn volatile_store<T>(dst: *mut T, val: T);
1238 /// Performs a volatile load from the `src` pointer
1239 /// The pointer is not required to be aligned.
1241 /// This intrinsic does not have a stable counterpart.
1242 pub fn unaligned_volatile_load<T>(src: *const T) -> T;
1243 /// Performs a volatile store to the `dst` pointer.
1244 /// The pointer is not required to be aligned.
1246 /// This intrinsic does not have a stable counterpart.
1247 pub fn unaligned_volatile_store<T>(dst: *mut T, val: T);
1249 /// Returns the square root of an `f32`
1251 /// The stabilized version of this intrinsic is
1252 /// [`f32::sqrt`](../../std/primitive.f32.html#method.sqrt)
1253 pub fn sqrtf32(x: f32) -> f32;
1254 /// Returns the square root of an `f64`
1256 /// The stabilized version of this intrinsic is
1257 /// [`f64::sqrt`](../../std/primitive.f64.html#method.sqrt)
1258 pub fn sqrtf64(x: f64) -> f64;
1260 /// Raises an `f32` to an integer power.
1262 /// The stabilized version of this intrinsic is
1263 /// [`f32::powi`](../../std/primitive.f32.html#method.powi)
1264 pub fn powif32(a: f32, x: i32) -> f32;
1265 /// Raises an `f64` to an integer power.
1267 /// The stabilized version of this intrinsic is
1268 /// [`f64::powi`](../../std/primitive.f64.html#method.powi)
1269 pub fn powif64(a: f64, x: i32) -> f64;
1271 /// Returns the sine of an `f32`.
1273 /// The stabilized version of this intrinsic is
1274 /// [`f32::sin`](../../std/primitive.f32.html#method.sin)
1275 pub fn sinf32(x: f32) -> f32;
1276 /// Returns the sine of an `f64`.
1278 /// The stabilized version of this intrinsic is
1279 /// [`f64::sin`](../../std/primitive.f64.html#method.sin)
1280 pub fn sinf64(x: f64) -> f64;
1282 /// Returns the cosine of an `f32`.
1284 /// The stabilized version of this intrinsic is
1285 /// [`f32::cos`](../../std/primitive.f32.html#method.cos)
1286 pub fn cosf32(x: f32) -> f32;
1287 /// Returns the cosine of an `f64`.
1289 /// The stabilized version of this intrinsic is
1290 /// [`f64::cos`](../../std/primitive.f64.html#method.cos)
1291 pub fn cosf64(x: f64) -> f64;
1293 /// Raises an `f32` to an `f32` power.
1295 /// The stabilized version of this intrinsic is
1296 /// [`f32::powf`](../../std/primitive.f32.html#method.powf)
1297 pub fn powf32(a: f32, x: f32) -> f32;
1298 /// Raises an `f64` to an `f64` power.
1300 /// The stabilized version of this intrinsic is
1301 /// [`f64::powf`](../../std/primitive.f64.html#method.powf)
1302 pub fn powf64(a: f64, x: f64) -> f64;
1304 /// Returns the exponential of an `f32`.
1306 /// The stabilized version of this intrinsic is
1307 /// [`f32::exp`](../../std/primitive.f32.html#method.exp)
1308 pub fn expf32(x: f32) -> f32;
1309 /// Returns the exponential of an `f64`.
1311 /// The stabilized version of this intrinsic is
1312 /// [`f64::exp`](../../std/primitive.f64.html#method.exp)
1313 pub fn expf64(x: f64) -> f64;
1315 /// Returns 2 raised to the power of an `f32`.
1317 /// The stabilized version of this intrinsic is
1318 /// [`f32::exp2`](../../std/primitive.f32.html#method.exp2)
1319 pub fn exp2f32(x: f32) -> f32;
1320 /// Returns 2 raised to the power of an `f64`.
1322 /// The stabilized version of this intrinsic is
1323 /// [`f64::exp2`](../../std/primitive.f64.html#method.exp2)
1324 pub fn exp2f64(x: f64) -> f64;
1326 /// Returns the natural logarithm of an `f32`.
1328 /// The stabilized version of this intrinsic is
1329 /// [`f32::ln`](../../std/primitive.f32.html#method.ln)
1330 pub fn logf32(x: f32) -> f32;
1331 /// Returns the natural logarithm of an `f64`.
1333 /// The stabilized version of this intrinsic is
1334 /// [`f64::ln`](../../std/primitive.f64.html#method.ln)
1335 pub fn logf64(x: f64) -> f64;
1337 /// Returns the base 10 logarithm of an `f32`.
1339 /// The stabilized version of this intrinsic is
1340 /// [`f32::log10`](../../std/primitive.f32.html#method.log10)
1341 pub fn log10f32(x: f32) -> f32;
1342 /// Returns the base 10 logarithm of an `f64`.
1344 /// The stabilized version of this intrinsic is
1345 /// [`f64::log10`](../../std/primitive.f64.html#method.log10)
1346 pub fn log10f64(x: f64) -> f64;
1348 /// Returns the base 2 logarithm of an `f32`.
1350 /// The stabilized version of this intrinsic is
1351 /// [`f32::log2`](../../std/primitive.f32.html#method.log2)
1352 pub fn log2f32(x: f32) -> f32;
1353 /// Returns the base 2 logarithm of an `f64`.
1355 /// The stabilized version of this intrinsic is
1356 /// [`f64::log2`](../../std/primitive.f64.html#method.log2)
1357 pub fn log2f64(x: f64) -> f64;
1359 /// Returns `a * b + c` for `f32` values.
1361 /// The stabilized version of this intrinsic is
1362 /// [`f32::mul_add`](../../std/primitive.f32.html#method.mul_add)
1363 pub fn fmaf32(a: f32, b: f32, c: f32) -> f32;
1364 /// Returns `a * b + c` for `f64` values.
1366 /// The stabilized version of this intrinsic is
1367 /// [`f64::mul_add`](../../std/primitive.f64.html#method.mul_add)
1368 pub fn fmaf64(a: f64, b: f64, c: f64) -> f64;
1370 /// Returns the absolute value of an `f32`.
1372 /// The stabilized version of this intrinsic is
1373 /// [`f32::abs`](../../std/primitive.f32.html#method.abs)
1374 pub fn fabsf32(x: f32) -> f32;
1375 /// Returns the absolute value of an `f64`.
1377 /// The stabilized version of this intrinsic is
1378 /// [`f64::abs`](../../std/primitive.f64.html#method.abs)
1379 pub fn fabsf64(x: f64) -> f64;
1381 /// Returns the minimum of two `f32` values.
1383 /// Note that, unlike most intrinsics, this is safe to call;
1384 /// it does not require an `unsafe` block.
1385 /// Therefore, implementations must not require the user to uphold
1386 /// any safety invariants.
1388 /// The stabilized version of this intrinsic is
1390 pub fn minnumf32(x: f32, y: f32) -> f32;
1391 /// Returns the minimum of two `f64` values.
1393 /// Note that, unlike most intrinsics, this is safe to call;
1394 /// it does not require an `unsafe` block.
1395 /// Therefore, implementations must not require the user to uphold
1396 /// any safety invariants.
1398 /// The stabilized version of this intrinsic is
1400 pub fn minnumf64(x: f64, y: f64) -> f64;
1401 /// Returns the maximum of two `f32` values.
1403 /// Note that, unlike most intrinsics, this is safe to call;
1404 /// it does not require an `unsafe` block.
1405 /// Therefore, implementations must not require the user to uphold
1406 /// any safety invariants.
1408 /// The stabilized version of this intrinsic is
1410 pub fn maxnumf32(x: f32, y: f32) -> f32;
1411 /// Returns the maximum of two `f64` values.
1413 /// Note that, unlike most intrinsics, this is safe to call;
1414 /// it does not require an `unsafe` block.
1415 /// Therefore, implementations must not require the user to uphold
1416 /// any safety invariants.
1418 /// The stabilized version of this intrinsic is
1420 pub fn maxnumf64(x: f64, y: f64) -> f64;
1422 /// Copies the sign from `y` to `x` for `f32` values.
1424 /// The stabilized version of this intrinsic is
1425 /// [`f32::copysign`](../../std/primitive.f32.html#method.copysign)
1426 pub fn copysignf32(x: f32, y: f32) -> f32;
1427 /// Copies the sign from `y` to `x` for `f64` values.
1429 /// The stabilized version of this intrinsic is
1430 /// [`f64::copysign`](../../std/primitive.f64.html#method.copysign)
1431 pub fn copysignf64(x: f64, y: f64) -> f64;
1433 /// Returns the largest integer less than or equal to an `f32`.
1435 /// The stabilized version of this intrinsic is
1436 /// [`f32::floor`](../../std/primitive.f32.html#method.floor)
1437 pub fn floorf32(x: f32) -> f32;
1438 /// Returns the largest integer less than or equal to an `f64`.
1440 /// The stabilized version of this intrinsic is
1441 /// [`f64::floor`](../../std/primitive.f64.html#method.floor)
1442 pub fn floorf64(x: f64) -> f64;
1444 /// Returns the smallest integer greater than or equal to an `f32`.
1446 /// The stabilized version of this intrinsic is
1447 /// [`f32::ceil`](../../std/primitive.f32.html#method.ceil)
1448 pub fn ceilf32(x: f32) -> f32;
1449 /// Returns the smallest integer greater than or equal to an `f64`.
1451 /// The stabilized version of this intrinsic is
1452 /// [`f64::ceil`](../../std/primitive.f64.html#method.ceil)
1453 pub fn ceilf64(x: f64) -> f64;
1455 /// Returns the integer part of an `f32`.
1457 /// The stabilized version of this intrinsic is
1458 /// [`f32::trunc`](../../std/primitive.f32.html#method.trunc)
1459 pub fn truncf32(x: f32) -> f32;
1460 /// Returns the integer part of an `f64`.
1462 /// The stabilized version of this intrinsic is
1463 /// [`f64::trunc`](../../std/primitive.f64.html#method.trunc)
1464 pub fn truncf64(x: f64) -> f64;
1466 /// Returns the nearest integer to an `f32`. May raise an inexact floating-point exception
1467 /// if the argument is not an integer.
1468 pub fn rintf32(x: f32) -> f32;
1469 /// Returns the nearest integer to an `f64`. May raise an inexact floating-point exception
1470 /// if the argument is not an integer.
1471 pub fn rintf64(x: f64) -> f64;
1473 /// Returns the nearest integer to an `f32`.
1475 /// This intrinsic does not have a stable counterpart.
1476 pub fn nearbyintf32(x: f32) -> f32;
1477 /// Returns the nearest integer to an `f64`.
1479 /// This intrinsic does not have a stable counterpart.
1480 pub fn nearbyintf64(x: f64) -> f64;
1482 /// Returns the nearest integer to an `f32`. Rounds half-way cases away from zero.
1484 /// The stabilized version of this intrinsic is
1485 /// [`f32::round`](../../std/primitive.f32.html#method.round)
1486 pub fn roundf32(x: f32) -> f32;
1487 /// Returns the nearest integer to an `f64`. Rounds half-way cases away from zero.
1489 /// The stabilized version of this intrinsic is
1490 /// [`f64::round`](../../std/primitive.f64.html#method.round)
1491 pub fn roundf64(x: f64) -> f64;
1493 /// Float addition that allows optimizations based on algebraic rules.
1494 /// May assume inputs are finite.
1496 /// This intrinsic does not have a stable counterpart.
1497 pub fn fadd_fast<T: Copy>(a: T, b: T) -> T;
1499 /// Float subtraction that allows optimizations based on algebraic rules.
1500 /// May assume inputs are finite.
1502 /// This intrinsic does not have a stable counterpart.
1503 pub fn fsub_fast<T: Copy>(a: T, b: T) -> T;
1505 /// Float multiplication that allows optimizations based on algebraic rules.
1506 /// May assume inputs are finite.
1508 /// This intrinsic does not have a stable counterpart.
1509 pub fn fmul_fast<T: Copy>(a: T, b: T) -> T;
1511 /// Float division that allows optimizations based on algebraic rules.
1512 /// May assume inputs are finite.
1514 /// This intrinsic does not have a stable counterpart.
1515 pub fn fdiv_fast<T: Copy>(a: T, b: T) -> T;
1517 /// Float remainder that allows optimizations based on algebraic rules.
1518 /// May assume inputs are finite.
1520 /// This intrinsic does not have a stable counterpart.
1521 pub fn frem_fast<T: Copy>(a: T, b: T) -> T;
1523 /// Convert with LLVM’s fptoui/fptosi, which may return undef for values out of range
1524 /// (<https://github.com/rust-lang/rust/issues/10184>)
1526 /// Stabilized as [`f32::to_int_unchecked`] and [`f64::to_int_unchecked`].
1527 pub fn float_to_int_unchecked<Float: Copy, Int: Copy>(value: Float) -> Int;
1529 /// Returns the number of bits set in an integer type `T`
1531 /// Note that, unlike most intrinsics, this is safe to call;
1532 /// it does not require an `unsafe` block.
1533 /// Therefore, implementations must not require the user to uphold
1534 /// any safety invariants.
1536 /// The stabilized versions of this intrinsic are available on the integer
1537 /// primitives via the `count_ones` method. For example,
1538 /// [`u32::count_ones`]
1539 #[rustc_const_stable(feature = "const_ctpop", since = "1.40.0")]
1540 pub fn ctpop<T: Copy>(x: T) -> T;
1542 /// Returns the number of leading unset bits (zeroes) in an integer type `T`.
1544 /// Note that, unlike most intrinsics, this is safe to call;
1545 /// it does not require an `unsafe` block.
1546 /// Therefore, implementations must not require the user to uphold
1547 /// any safety invariants.
1549 /// The stabilized versions of this intrinsic are available on the integer
1550 /// primitives via the `leading_zeros` method. For example,
1551 /// [`u32::leading_zeros`]
1556 /// #![feature(core_intrinsics)]
1558 /// use std::intrinsics::ctlz;
1560 /// let x = 0b0001_1100_u8;
1561 /// let num_leading = ctlz(x);
1562 /// assert_eq!(num_leading, 3);
1565 /// An `x` with value `0` will return the bit width of `T`.
1568 /// #![feature(core_intrinsics)]
1570 /// use std::intrinsics::ctlz;
1573 /// let num_leading = ctlz(x);
1574 /// assert_eq!(num_leading, 16);
1576 #[rustc_const_stable(feature = "const_ctlz", since = "1.40.0")]
1577 pub fn ctlz<T: Copy>(x: T) -> T;
1579 /// Like `ctlz`, but extra-unsafe as it returns `undef` when
1580 /// given an `x` with value `0`.
1582 /// This intrinsic does not have a stable counterpart.
1587 /// #![feature(core_intrinsics)]
1589 /// use std::intrinsics::ctlz_nonzero;
1591 /// let x = 0b0001_1100_u8;
1592 /// let num_leading = unsafe { ctlz_nonzero(x) };
1593 /// assert_eq!(num_leading, 3);
1595 #[rustc_const_stable(feature = "constctlz", since = "1.50.0")]
1596 pub fn ctlz_nonzero<T: Copy>(x: T) -> T;
1598 /// Returns the number of trailing unset bits (zeroes) in an integer type `T`.
1600 /// Note that, unlike most intrinsics, this is safe to call;
1601 /// it does not require an `unsafe` block.
1602 /// Therefore, implementations must not require the user to uphold
1603 /// any safety invariants.
1605 /// The stabilized versions of this intrinsic are available on the integer
1606 /// primitives via the `trailing_zeros` method. For example,
1607 /// [`u32::trailing_zeros`]
1612 /// #![feature(core_intrinsics)]
1614 /// use std::intrinsics::cttz;
1616 /// let x = 0b0011_1000_u8;
1617 /// let num_trailing = cttz(x);
1618 /// assert_eq!(num_trailing, 3);
1621 /// An `x` with value `0` will return the bit width of `T`:
1624 /// #![feature(core_intrinsics)]
1626 /// use std::intrinsics::cttz;
1629 /// let num_trailing = cttz(x);
1630 /// assert_eq!(num_trailing, 16);
1632 #[rustc_const_stable(feature = "const_cttz", since = "1.40.0")]
1633 pub fn cttz<T: Copy>(x: T) -> T;
1635 /// Like `cttz`, but extra-unsafe as it returns `undef` when
1636 /// given an `x` with value `0`.
1638 /// This intrinsic does not have a stable counterpart.
1643 /// #![feature(core_intrinsics)]
1645 /// use std::intrinsics::cttz_nonzero;
1647 /// let x = 0b0011_1000_u8;
1648 /// let num_trailing = unsafe { cttz_nonzero(x) };
1649 /// assert_eq!(num_trailing, 3);
1651 #[rustc_const_stable(feature = "const_cttz_nonzero", since = "1.53.0")]
1652 pub fn cttz_nonzero<T: Copy>(x: T) -> T;
1654 /// Reverses the bytes in an integer type `T`.
1656 /// Note that, unlike most intrinsics, this is safe to call;
1657 /// it does not require an `unsafe` block.
1658 /// Therefore, implementations must not require the user to uphold
1659 /// any safety invariants.
1661 /// The stabilized versions of this intrinsic are available on the integer
1662 /// primitives via the `swap_bytes` method. For example,
1663 /// [`u32::swap_bytes`]
1664 #[rustc_const_stable(feature = "const_bswap", since = "1.40.0")]
1665 pub fn bswap<T: Copy>(x: T) -> T;
1667 /// Reverses the bits in an integer type `T`.
1669 /// Note that, unlike most intrinsics, this is safe to call;
1670 /// it does not require an `unsafe` block.
1671 /// Therefore, implementations must not require the user to uphold
1672 /// any safety invariants.
1674 /// The stabilized versions of this intrinsic are available on the integer
1675 /// primitives via the `reverse_bits` method. For example,
1676 /// [`u32::reverse_bits`]
1677 #[rustc_const_stable(feature = "const_bitreverse", since = "1.40.0")]
1678 pub fn bitreverse<T: Copy>(x: T) -> T;
1680 /// Performs checked integer addition.
1682 /// Note that, unlike most intrinsics, this is safe to call;
1683 /// it does not require an `unsafe` block.
1684 /// Therefore, implementations must not require the user to uphold
1685 /// any safety invariants.
1687 /// The stabilized versions of this intrinsic are available on the integer
1688 /// primitives via the `overflowing_add` method. For example,
1689 /// [`u32::overflowing_add`]
1690 #[rustc_const_stable(feature = "const_int_overflow", since = "1.40.0")]
1691 pub fn add_with_overflow<T: Copy>(x: T, y: T) -> (T, bool);
1693 /// Performs checked integer subtraction
1695 /// Note that, unlike most intrinsics, this is safe to call;
1696 /// it does not require an `unsafe` block.
1697 /// Therefore, implementations must not require the user to uphold
1698 /// any safety invariants.
1700 /// The stabilized versions of this intrinsic are available on the integer
1701 /// primitives via the `overflowing_sub` method. For example,
1702 /// [`u32::overflowing_sub`]
1703 #[rustc_const_stable(feature = "const_int_overflow", since = "1.40.0")]
1704 pub fn sub_with_overflow<T: Copy>(x: T, y: T) -> (T, bool);
1706 /// Performs checked integer multiplication
1708 /// Note that, unlike most intrinsics, this is safe to call;
1709 /// it does not require an `unsafe` block.
1710 /// Therefore, implementations must not require the user to uphold
1711 /// any safety invariants.
1713 /// The stabilized versions of this intrinsic are available on the integer
1714 /// primitives via the `overflowing_mul` method. For example,
1715 /// [`u32::overflowing_mul`]
1716 #[rustc_const_stable(feature = "const_int_overflow", since = "1.40.0")]
1717 pub fn mul_with_overflow<T: Copy>(x: T, y: T) -> (T, bool);
1719 /// Performs an exact division, resulting in undefined behavior where
1720 /// `x % y != 0` or `y == 0` or `x == T::MIN && y == -1`
1722 /// This intrinsic does not have a stable counterpart.
1723 pub fn exact_div<T: Copy>(x: T, y: T) -> T;
1725 /// Performs an unchecked division, resulting in undefined behavior
1726 /// where `y == 0` or `x == T::MIN && y == -1`
1728 /// Safe wrappers for this intrinsic are available on the integer
1729 /// primitives via the `checked_div` method. For example,
1730 /// [`u32::checked_div`]
1731 #[rustc_const_stable(feature = "const_int_unchecked_div", since = "1.52.0")]
1732 pub fn unchecked_div<T: Copy>(x: T, y: T) -> T;
1733 /// Returns the remainder of an unchecked division, resulting in
1734 /// undefined behavior when `y == 0` or `x == T::MIN && y == -1`
1736 /// Safe wrappers for this intrinsic are available on the integer
1737 /// primitives via the `checked_rem` method. For example,
1738 /// [`u32::checked_rem`]
1739 #[rustc_const_stable(feature = "const_int_unchecked_rem", since = "1.52.0")]
1740 pub fn unchecked_rem<T: Copy>(x: T, y: T) -> T;
1742 /// Performs an unchecked left shift, resulting in undefined behavior when
1743 /// `y < 0` or `y >= N`, where N is the width of T in bits.
1745 /// Safe wrappers for this intrinsic are available on the integer
1746 /// primitives via the `checked_shl` method. For example,
1747 /// [`u32::checked_shl`]
1748 #[rustc_const_stable(feature = "const_int_unchecked", since = "1.40.0")]
1749 pub fn unchecked_shl<T: Copy>(x: T, y: T) -> T;
1750 /// Performs an unchecked right shift, resulting in undefined behavior when
1751 /// `y < 0` or `y >= N`, where N is the width of T in bits.
1753 /// Safe wrappers for this intrinsic are available on the integer
1754 /// primitives via the `checked_shr` method. For example,
1755 /// [`u32::checked_shr`]
1756 #[rustc_const_stable(feature = "const_int_unchecked", since = "1.40.0")]
1757 pub fn unchecked_shr<T: Copy>(x: T, y: T) -> T;
1759 /// Returns the result of an unchecked addition, resulting in
1760 /// undefined behavior when `x + y > T::MAX` or `x + y < T::MIN`.
1762 /// This intrinsic does not have a stable counterpart.
1763 #[rustc_const_unstable(feature = "const_int_unchecked_arith", issue = "none")]
1764 pub fn unchecked_add<T: Copy>(x: T, y: T) -> T;
1766 /// Returns the result of an unchecked subtraction, resulting in
1767 /// undefined behavior when `x - y > T::MAX` or `x - y < T::MIN`.
1769 /// This intrinsic does not have a stable counterpart.
1770 #[rustc_const_unstable(feature = "const_int_unchecked_arith", issue = "none")]
1771 pub fn unchecked_sub<T: Copy>(x: T, y: T) -> T;
1773 /// Returns the result of an unchecked multiplication, resulting in
1774 /// undefined behavior when `x * y > T::MAX` or `x * y < T::MIN`.
1776 /// This intrinsic does not have a stable counterpart.
1777 #[rustc_const_unstable(feature = "const_int_unchecked_arith", issue = "none")]
1778 pub fn unchecked_mul<T: Copy>(x: T, y: T) -> T;
1780 /// Performs rotate left.
1782 /// Note that, unlike most intrinsics, this is safe to call;
1783 /// it does not require an `unsafe` block.
1784 /// Therefore, implementations must not require the user to uphold
1785 /// any safety invariants.
1787 /// The stabilized versions of this intrinsic are available on the integer
1788 /// primitives via the `rotate_left` method. For example,
1789 /// [`u32::rotate_left`]
1790 #[rustc_const_stable(feature = "const_int_rotate", since = "1.40.0")]
1791 pub fn rotate_left<T: Copy>(x: T, y: T) -> T;
1793 /// Performs rotate right.
1795 /// Note that, unlike most intrinsics, this is safe to call;
1796 /// it does not require an `unsafe` block.
1797 /// Therefore, implementations must not require the user to uphold
1798 /// any safety invariants.
1800 /// The stabilized versions of this intrinsic are available on the integer
1801 /// primitives via the `rotate_right` method. For example,
1802 /// [`u32::rotate_right`]
1803 #[rustc_const_stable(feature = "const_int_rotate", since = "1.40.0")]
1804 pub fn rotate_right<T: Copy>(x: T, y: T) -> T;
1806 /// Returns (a + b) mod 2<sup>N</sup>, where N is the width of T in bits.
1808 /// Note that, unlike most intrinsics, this is safe to call;
1809 /// it does not require an `unsafe` block.
1810 /// Therefore, implementations must not require the user to uphold
1811 /// any safety invariants.
1813 /// The stabilized versions of this intrinsic are available on the integer
1814 /// primitives via the `wrapping_add` method. For example,
1815 /// [`u32::wrapping_add`]
1816 #[rustc_const_stable(feature = "const_int_wrapping", since = "1.40.0")]
1817 pub fn wrapping_add<T: Copy>(a: T, b: T) -> T;
1818 /// Returns (a - b) mod 2<sup>N</sup>, where N is the width of T in bits.
1820 /// Note that, unlike most intrinsics, this is safe to call;
1821 /// it does not require an `unsafe` block.
1822 /// Therefore, implementations must not require the user to uphold
1823 /// any safety invariants.
1825 /// The stabilized versions of this intrinsic are available on the integer
1826 /// primitives via the `wrapping_sub` method. For example,
1827 /// [`u32::wrapping_sub`]
1828 #[rustc_const_stable(feature = "const_int_wrapping", since = "1.40.0")]
1829 pub fn wrapping_sub<T: Copy>(a: T, b: T) -> T;
1830 /// Returns (a * b) mod 2<sup>N</sup>, where N is the width of T in bits.
1832 /// Note that, unlike most intrinsics, this is safe to call;
1833 /// it does not require an `unsafe` block.
1834 /// Therefore, implementations must not require the user to uphold
1835 /// any safety invariants.
1837 /// The stabilized versions of this intrinsic are available on the integer
1838 /// primitives via the `wrapping_mul` method. For example,
1839 /// [`u32::wrapping_mul`]
1840 #[rustc_const_stable(feature = "const_int_wrapping", since = "1.40.0")]
1841 pub fn wrapping_mul<T: Copy>(a: T, b: T) -> T;
1843 /// Computes `a + b`, saturating at numeric bounds.
1845 /// Note that, unlike most intrinsics, this is safe to call;
1846 /// it does not require an `unsafe` block.
1847 /// Therefore, implementations must not require the user to uphold
1848 /// any safety invariants.
1850 /// The stabilized versions of this intrinsic are available on the integer
1851 /// primitives via the `saturating_add` method. For example,
1852 /// [`u32::saturating_add`]
1853 #[rustc_const_stable(feature = "const_int_saturating", since = "1.40.0")]
1854 pub fn saturating_add<T: Copy>(a: T, b: T) -> T;
1855 /// Computes `a - b`, saturating at numeric bounds.
1857 /// Note that, unlike most intrinsics, this is safe to call;
1858 /// it does not require an `unsafe` block.
1859 /// Therefore, implementations must not require the user to uphold
1860 /// any safety invariants.
1862 /// The stabilized versions of this intrinsic are available on the integer
1863 /// primitives via the `saturating_sub` method. For example,
1864 /// [`u32::saturating_sub`]
1865 #[rustc_const_stable(feature = "const_int_saturating", since = "1.40.0")]
1866 pub fn saturating_sub<T: Copy>(a: T, b: T) -> T;
1868 /// Returns the value of the discriminant for the variant in 'v';
1869 /// if `T` has no discriminant, returns `0`.
1871 /// Note that, unlike most intrinsics, this is safe to call;
1872 /// it does not require an `unsafe` block.
1873 /// Therefore, implementations must not require the user to uphold
1874 /// any safety invariants.
1876 /// The stabilized version of this intrinsic is [`core::mem::discriminant`].
1877 #[rustc_const_unstable(feature = "const_discriminant", issue = "69821")]
1878 pub fn discriminant_value<T>(v: &T) -> <T as DiscriminantKind>::Discriminant;
1880 /// Returns the number of variants of the type `T` cast to a `usize`;
1881 /// if `T` has no variants, returns `0`. Uninhabited variants will be counted.
1883 /// Note that, unlike most intrinsics, this is safe to call;
1884 /// it does not require an `unsafe` block.
1885 /// Therefore, implementations must not require the user to uphold
1886 /// any safety invariants.
1888 /// The to-be-stabilized version of this intrinsic is [`mem::variant_count`].
1889 #[rustc_const_unstable(feature = "variant_count", issue = "73662")]
1890 pub fn variant_count<T>() -> usize;
1892 /// Rust's "try catch" construct which invokes the function pointer `try_fn`
1893 /// with the data pointer `data`.
1895 /// The third argument is a function called if a panic occurs. This function
1896 /// takes the data pointer and a pointer to the target-specific exception
1897 /// object that was caught. For more information see the compiler's
1898 /// source as well as std's catch implementation.
1899 pub fn r#try(try_fn: fn(*mut u8), data: *mut u8, catch_fn: fn(*mut u8, *mut u8)) -> i32;
1901 /// Emits a `!nontemporal` store according to LLVM (see their docs).
1902 /// Probably will never become stable.
1903 pub fn nontemporal_store<T>(ptr: *mut T, val: T);
1905 /// See documentation of `<*const T>::offset_from` for details.
1906 #[rustc_const_unstable(feature = "const_ptr_offset_from", issue = "92980")]
1907 pub fn ptr_offset_from<T>(ptr: *const T, base: *const T) -> isize;
1909 /// See documentation of `<*const T>::guaranteed_eq` for details.
1911 /// Note that, unlike most intrinsics, this is safe to call;
1912 /// it does not require an `unsafe` block.
1913 /// Therefore, implementations must not require the user to uphold
1914 /// any safety invariants.
1915 #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
1916 pub fn ptr_guaranteed_eq<T>(ptr: *const T, other: *const T) -> bool;
1918 /// See documentation of `<*const T>::guaranteed_ne` for details.
1920 /// Note that, unlike most intrinsics, this is safe to call;
1921 /// it does not require an `unsafe` block.
1922 /// Therefore, implementations must not require the user to uphold
1923 /// any safety invariants.
1924 #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
1925 pub fn ptr_guaranteed_ne<T>(ptr: *const T, other: *const T) -> bool;
1927 /// Allocates a block of memory at compile time.
1928 /// At runtime, just returns a null pointer.
1932 /// - The `align` argument must be a power of two.
1933 /// - At compile time, a compile error occurs if this constraint is violated.
1934 /// - At runtime, it is not checked.
1935 #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
1936 pub fn const_allocate(size: usize, align: usize) -> *mut u8;
1938 /// Deallocates a memory which allocated by `intrinsics::const_allocate` at compile time.
1939 /// At runtime, does nothing.
1943 /// - The `align` argument must be a power of two.
1944 /// - At compile time, a compile error occurs if this constraint is violated.
1945 /// - At runtime, it is not checked.
1946 /// - If the `ptr` is created in an another const, this intrinsic doesn't deallocate it.
1947 /// - If the `ptr` is pointing to a local variable, this intrinsic doesn't deallocate it.
1948 #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
1949 pub fn const_deallocate(ptr: *mut u8, size: usize, align: usize);
1951 /// Determines whether the raw bytes of the two values are equal.
1953 /// This is particularly handy for arrays, since it allows things like just
1954 /// comparing `i96`s instead of forcing `alloca`s for `[6 x i16]`.
1956 /// Above some backend-decided threshold this will emit calls to `memcmp`,
1957 /// like slice equality does, instead of causing massive code size.
1961 /// It's UB to call this if any of the *bytes* in `*a` or `*b` are uninitialized.
1962 /// Note that this is a stricter criterion than just the *values* being
1963 /// fully-initialized: if `T` has padding, it's UB to call this intrinsic.
1965 /// (The implementation is allowed to branch on the results of comparisons,
1966 /// which is UB if any of their inputs are `undef`.)
1967 #[rustc_const_unstable(feature = "const_intrinsic_raw_eq", issue = "none")]
1968 pub fn raw_eq<T>(a: &T, b: &T) -> bool;
1970 /// See documentation of [`std::hint::black_box`] for details.
1972 /// [`std::hint::black_box`]: crate::hint::black_box
1973 #[rustc_const_unstable(feature = "const_black_box", issue = "none")]
1974 pub fn black_box<T>(dummy: T) -> T;
1977 // Some functions are defined here because they accidentally got made
1978 // available in this module on stable. See <https://github.com/rust-lang/rust/issues/15702>.
1979 // (`transmute` also falls into this category, but it cannot be wrapped due to the
1980 // check that `T` and `U` have the same size.)
1982 /// Check that the preconditions of an unsafe function are followed, if debug_assertions are on,
1983 /// and only at runtime.
1987 /// Invoking this macro is only sound if the following code is already UB when the passed
1988 /// expression evaluates to false.
1990 /// This macro expands to a check at runtime if debug_assertions is set. It has no effect at
1991 /// compile time, but the semantics of the contained `const_eval_select` must be the same at
1992 /// runtime and at compile time. Thus if the expression evaluates to false, this macro produces
1993 /// different behavior at compile time and at runtime, and invoking it is incorrect.
1995 /// So in a sense it is UB if this macro is useful, but we expect callers of `unsafe fn` to make
1996 /// the occasional mistake, and this check should help them figure things out.
1997 #[allow_internal_unstable(const_eval_select)] // permit this to be called in stably-const fn
1998 macro_rules! assert_unsafe_precondition {
2000 if cfg!(debug_assertions) {
2001 // Use a closure so that we can capture arbitrary expressions from the invocation
2004 // abort instead of panicking to reduce impact on code size
2005 ::core::intrinsics::abort();
2008 const fn comptime() {}
2010 ::core::intrinsics::const_eval_select((), comptime, runtime);
2014 pub(crate) use assert_unsafe_precondition;
2016 /// Checks whether `ptr` is properly aligned with respect to
2017 /// `align_of::<T>()`.
2018 pub(crate) fn is_aligned_and_not_null<T>(ptr: *const T) -> bool {
2019 !ptr.is_null() && ptr.addr() % mem::align_of::<T>() == 0
2022 /// Checks whether the regions of memory starting at `src` and `dst` of size
2023 /// `count * size_of::<T>()` do *not* overlap.
2024 pub(crate) fn is_nonoverlapping<T>(src: *const T, dst: *const T, count: usize) -> bool {
2025 let src_usize = src.addr();
2026 let dst_usize = dst.addr();
2027 let size = mem::size_of::<T>().checked_mul(count).unwrap();
2028 let diff = if src_usize > dst_usize { src_usize - dst_usize } else { dst_usize - src_usize };
2029 // If the absolute distance between the ptrs is at least as big as the size of the buffer,
2030 // they do not overlap.
2034 /// Copies `count * size_of::<T>()` bytes from `src` to `dst`. The source
2035 /// and destination must *not* overlap.
2037 /// For regions of memory which might overlap, use [`copy`] instead.
2039 /// `copy_nonoverlapping` is semantically equivalent to C's [`memcpy`], but
2040 /// with the argument order swapped.
2042 /// [`memcpy`]: https://en.cppreference.com/w/c/string/byte/memcpy
2046 /// Behavior is undefined if any of the following conditions are violated:
2048 /// * `src` must be [valid] for reads of `count * size_of::<T>()` bytes.
2050 /// * `dst` must be [valid] for writes of `count * size_of::<T>()` bytes.
2052 /// * Both `src` and `dst` must be properly aligned.
2054 /// * The region of memory beginning at `src` with a size of `count *
2055 /// size_of::<T>()` bytes must *not* overlap with the region of memory
2056 /// beginning at `dst` with the same size.
2058 /// Like [`read`], `copy_nonoverlapping` creates a bitwise copy of `T`, regardless of
2059 /// whether `T` is [`Copy`]. If `T` is not [`Copy`], using *both* the values
2060 /// in the region beginning at `*src` and the region beginning at `*dst` can
2061 /// [violate memory safety][read-ownership].
2063 /// Note that even if the effectively copied size (`count * size_of::<T>()`) is
2064 /// `0`, the pointers must be non-null and properly aligned.
2066 /// [`read`]: crate::ptr::read
2067 /// [read-ownership]: crate::ptr::read#ownership-of-the-returned-value
2068 /// [valid]: crate::ptr#safety
2072 /// Manually implement [`Vec::append`]:
2077 /// /// Moves all the elements of `src` into `dst`, leaving `src` empty.
2078 /// fn append<T>(dst: &mut Vec<T>, src: &mut Vec<T>) {
2079 /// let src_len = src.len();
2080 /// let dst_len = dst.len();
2082 /// // Ensure that `dst` has enough capacity to hold all of `src`.
2083 /// dst.reserve(src_len);
2086 /// // The call to offset is always safe because `Vec` will never
2087 /// // allocate more than `isize::MAX` bytes.
2088 /// let dst_ptr = dst.as_mut_ptr().offset(dst_len as isize);
2089 /// let src_ptr = src.as_ptr();
2091 /// // Truncate `src` without dropping its contents. We do this first,
2092 /// // to avoid problems in case something further down panics.
2095 /// // The two regions cannot overlap because mutable references do
2096 /// // not alias, and two different vectors cannot own the same
2098 /// ptr::copy_nonoverlapping(src_ptr, dst_ptr, src_len);
2100 /// // Notify `dst` that it now holds the contents of `src`.
2101 /// dst.set_len(dst_len + src_len);
2105 /// let mut a = vec!['r'];
2106 /// let mut b = vec!['u', 's', 't'];
2108 /// append(&mut a, &mut b);
2110 /// assert_eq!(a, &['r', 'u', 's', 't']);
2111 /// assert!(b.is_empty());
2114 /// [`Vec::append`]: ../../std/vec/struct.Vec.html#method.append
2115 #[doc(alias = "memcpy")]
2116 #[stable(feature = "rust1", since = "1.0.0")]
2117 #[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
2119 pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize) {
2120 extern "rust-intrinsic" {
2121 #[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
2122 pub fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
2125 // SAFETY: the safety contract for `copy_nonoverlapping` must be
2126 // upheld by the caller.
2128 assert_unsafe_precondition!(
2129 is_aligned_and_not_null(src)
2130 && is_aligned_and_not_null(dst)
2131 && is_nonoverlapping(src, dst, count)
2133 copy_nonoverlapping(src, dst, count)
2137 /// Copies `count * size_of::<T>()` bytes from `src` to `dst`. The source
2138 /// and destination may overlap.
2140 /// If the source and destination will *never* overlap,
2141 /// [`copy_nonoverlapping`] can be used instead.
2143 /// `copy` is semantically equivalent to C's [`memmove`], but with the argument
2144 /// order swapped. Copying takes place as if the bytes were copied from `src`
2145 /// to a temporary array and then copied from the array to `dst`.
2147 /// [`memmove`]: https://en.cppreference.com/w/c/string/byte/memmove
2151 /// Behavior is undefined if any of the following conditions are violated:
2153 /// * `src` must be [valid] for reads of `count * size_of::<T>()` bytes.
2155 /// * `dst` must be [valid] for writes of `count * size_of::<T>()` bytes.
2157 /// * Both `src` and `dst` must be properly aligned.
2159 /// Like [`read`], `copy` creates a bitwise copy of `T`, regardless of
2160 /// whether `T` is [`Copy`]. If `T` is not [`Copy`], using both the values
2161 /// in the region beginning at `*src` and the region beginning at `*dst` can
2162 /// [violate memory safety][read-ownership].
2164 /// Note that even if the effectively copied size (`count * size_of::<T>()`) is
2165 /// `0`, the pointers must be non-null and properly aligned.
2167 /// [`read`]: crate::ptr::read
2168 /// [read-ownership]: crate::ptr::read#ownership-of-the-returned-value
2169 /// [valid]: crate::ptr#safety
2173 /// Efficiently create a Rust vector from an unsafe buffer:
2180 /// /// * `ptr` must be correctly aligned for its type and non-zero.
2181 /// /// * `ptr` must be valid for reads of `elts` contiguous elements of type `T`.
2182 /// /// * Those elements must not be used after calling this function unless `T: Copy`.
2183 /// # #[allow(dead_code)]
2184 /// unsafe fn from_buf_raw<T>(ptr: *const T, elts: usize) -> Vec<T> {
2185 /// let mut dst = Vec::with_capacity(elts);
2187 /// // SAFETY: Our precondition ensures the source is aligned and valid,
2188 /// // and `Vec::with_capacity` ensures that we have usable space to write them.
2189 /// ptr::copy(ptr, dst.as_mut_ptr(), elts);
2191 /// // SAFETY: We created it with this much capacity earlier,
2192 /// // and the previous `copy` has initialized these elements.
2193 /// dst.set_len(elts);
2197 #[doc(alias = "memmove")]
2198 #[stable(feature = "rust1", since = "1.0.0")]
2199 #[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
2201 pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
2202 extern "rust-intrinsic" {
2203 #[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
2204 fn copy<T>(src: *const T, dst: *mut T, count: usize);
2207 // SAFETY: the safety contract for `copy` must be upheld by the caller.
2209 assert_unsafe_precondition!(is_aligned_and_not_null(src) && is_aligned_and_not_null(dst));
2210 copy(src, dst, count)
2214 /// Sets `count * size_of::<T>()` bytes of memory starting at `dst` to
2217 /// `write_bytes` is similar to C's [`memset`], but sets `count *
2218 /// size_of::<T>()` bytes to `val`.
2220 /// [`memset`]: https://en.cppreference.com/w/c/string/byte/memset
2224 /// Behavior is undefined if any of the following conditions are violated:
2226 /// * `dst` must be [valid] for writes of `count * size_of::<T>()` bytes.
2228 /// * `dst` must be properly aligned.
2230 /// Additionally, the caller must ensure that writing `count *
2231 /// size_of::<T>()` bytes to the given region of memory results in a valid
2232 /// value of `T`. Using a region of memory typed as a `T` that contains an
2233 /// invalid value of `T` is undefined behavior.
2235 /// Note that even if the effectively copied size (`count * size_of::<T>()`) is
2236 /// `0`, the pointer must be non-null and properly aligned.
2238 /// [valid]: crate::ptr#safety
2247 /// let mut vec = vec![0u32; 4];
2249 /// let vec_ptr = vec.as_mut_ptr();
2250 /// ptr::write_bytes(vec_ptr, 0xfe, 2);
2252 /// assert_eq!(vec, [0xfefefefe, 0xfefefefe, 0, 0]);
2255 /// Creating an invalid value:
2260 /// let mut v = Box::new(0i32);
2263 /// // Leaks the previously held value by overwriting the `Box<T>` with
2264 /// // a null pointer.
2265 /// ptr::write_bytes(&mut v as *mut Box<i32>, 0, 1);
2268 /// // At this point, using or dropping `v` results in undefined behavior.
2269 /// // drop(v); // ERROR
2271 /// // Even leaking `v` "uses" it, and hence is undefined behavior.
2272 /// // mem::forget(v); // ERROR
2274 /// // In fact, `v` is invalid according to basic type layout invariants, so *any*
2275 /// // operation touching it is undefined behavior.
2276 /// // let v2 = v; // ERROR
2279 /// // Let us instead put in a valid value
2280 /// ptr::write(&mut v as *mut Box<i32>, Box::new(42i32));
2283 /// // Now the box is fine
2284 /// assert_eq!(*v, 42);
2286 #[stable(feature = "rust1", since = "1.0.0")]
2287 #[rustc_const_unstable(feature = "const_ptr_write", issue = "86302")]
2289 pub const unsafe fn write_bytes<T>(dst: *mut T, val: u8, count: usize) {
2290 extern "rust-intrinsic" {
2291 #[rustc_const_unstable(feature = "const_ptr_write", issue = "86302")]
2292 fn write_bytes<T>(dst: *mut T, val: u8, count: usize);
2295 // SAFETY: the safety contract for `write_bytes` must be upheld by the caller.
2297 assert_unsafe_precondition!(is_aligned_and_not_null(dst));
2298 write_bytes(dst, val, count)
2302 /// Selects which function to call depending on the context.
2304 /// If this function is evaluated at compile-time, then a call to this
2305 /// intrinsic will be replaced with a call to `called_in_const`. It gets
2306 /// replaced with a call to `called_at_rt` otherwise.
2308 /// # Type Requirements
2310 /// The two functions must be both function items. They cannot be function
2311 /// pointers or closures.
2313 /// `arg` will be the arguments that will be passed to either one of the
2314 /// two functions, therefore, both functions must accept the same type of
2315 /// arguments. Both functions must return RET.
2319 /// The two functions must behave observably equivalent. Safe code in other
2320 /// crates may assume that calling a `const fn` at compile-time and at run-time
2321 /// produces the same result. A function that produces a different result when
2322 /// evaluated at run-time, or has any other observable side-effects, is
2325 /// Here is an example of how this could cause a problem:
2327 /// #![feature(const_eval_select)]
2328 /// use std::hint::unreachable_unchecked;
2329 /// use std::intrinsics::const_eval_select;
2332 /// pub const fn inconsistent() -> i32 {
2333 /// fn runtime() -> i32 { 1 }
2334 /// const fn compiletime() -> i32 { 2 }
2337 // // ⚠ This code violates the required equivalence of `compiletime`
2338 /// // and `runtime`.
2339 /// const_eval_select((), compiletime, runtime)
2344 /// const X: i32 = inconsistent();
2345 /// let x = inconsistent();
2346 /// if x != X { unsafe { unreachable_unchecked(); }}
2349 /// This code causes Undefined Behavior when being run, since the
2350 /// `unreachable_unchecked` is actually being reached. The bug is in *crate A*,
2351 /// which violates the principle that a `const fn` must behave the same at
2352 /// compile-time and at run-time. The unsafe code in crate B is fine.
2354 feature = "const_eval_select",
2356 reason = "const_eval_select will never be stable"
2358 #[rustc_const_unstable(feature = "const_eval_select", issue = "none")]
2359 #[lang = "const_eval_select"]
2360 #[rustc_do_not_const_check]
2361 pub const unsafe fn const_eval_select<ARG, F, G, RET>(
2363 _called_in_const: F,
2367 F: ~const FnOnce<ARG, Output = RET>,
2368 G: FnOnce<ARG, Output = RET> + ~const Destruct,
2370 called_at_rt.call_once(arg)
2374 feature = "const_eval_select",
2376 reason = "const_eval_select will never be stable"
2378 #[rustc_const_unstable(feature = "const_eval_select", issue = "none")]
2379 #[lang = "const_eval_select_ct"]
2380 pub const unsafe fn const_eval_select_ct<ARG, F, G, RET>(
2386 F: ~const FnOnce<ARG, Output = RET>,
2387 G: FnOnce<ARG, Output = RET> + ~const Destruct,
2389 called_in_const.call_once(arg)