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::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_unstable(feature = "const_unreachable_unchecked", issue = "53188")]
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 #[rustc_const_unstable(feature = "const_pref_align_of", issue = "none")]
815 pub fn pref_align_of<T>() -> usize;
817 /// The size of the referenced value in bytes.
819 /// The stabilized version of this intrinsic is [`mem::size_of_val`].
820 #[rustc_const_unstable(feature = "const_size_of_val", issue = "46571")]
821 pub fn size_of_val<T: ?Sized>(_: *const T) -> usize;
822 /// The required alignment of the referenced value.
824 /// The stabilized version of this intrinsic is [`core::mem::align_of_val`].
825 #[rustc_const_unstable(feature = "const_align_of_val", issue = "46571")]
826 pub fn min_align_of_val<T: ?Sized>(_: *const T) -> usize;
828 /// Gets a static string slice containing the name of a type.
830 /// Note that, unlike most intrinsics, this is safe to call;
831 /// it does not require an `unsafe` block.
832 /// Therefore, implementations must not require the user to uphold
833 /// any safety invariants.
835 /// The stabilized version of this intrinsic is [`core::any::type_name`].
836 #[rustc_const_unstable(feature = "const_type_name", issue = "63084")]
837 pub fn type_name<T: ?Sized>() -> &'static str;
839 /// Gets an identifier which is globally unique to the specified type. This
840 /// function will return the same value for a type regardless of whichever
841 /// crate it is invoked in.
843 /// Note that, unlike most intrinsics, this is safe to call;
844 /// it does not require an `unsafe` block.
845 /// Therefore, implementations must not require the user to uphold
846 /// any safety invariants.
848 /// The stabilized version of this intrinsic is [`core::any::TypeId::of`].
849 #[rustc_const_unstable(feature = "const_type_id", issue = "77125")]
850 pub fn type_id<T: ?Sized + 'static>() -> u64;
852 /// A guard for unsafe functions that cannot ever be executed if `T` is uninhabited:
853 /// This will statically either panic, or do nothing.
855 /// This intrinsic does not have a stable counterpart.
856 #[rustc_const_unstable(feature = "const_assert_type", issue = "none")]
857 pub fn assert_inhabited<T>();
859 /// A guard for unsafe functions that cannot ever be executed if `T` does not permit
860 /// zero-initialization: This will statically either panic, or do nothing.
862 /// This intrinsic does not have a stable counterpart.
863 pub fn assert_zero_valid<T>();
865 /// A guard for unsafe functions that cannot ever be executed if `T` has invalid
866 /// bit patterns: This will statically either panic, or do nothing.
868 /// This intrinsic does not have a stable counterpart.
869 pub fn assert_uninit_valid<T>();
871 /// Gets a reference to a static `Location` indicating where it was called.
873 /// Note that, unlike most intrinsics, this is safe to call;
874 /// it does not require an `unsafe` block.
875 /// Therefore, implementations must not require the user to uphold
876 /// any safety invariants.
878 /// Consider using [`core::panic::Location::caller`] instead.
879 #[rustc_const_unstable(feature = "const_caller_location", issue = "76156")]
880 pub fn caller_location() -> &'static crate::panic::Location<'static>;
882 /// Moves a value out of scope without running drop glue.
884 /// This exists solely for [`mem::forget_unsized`]; normal `forget` uses
885 /// `ManuallyDrop` instead.
887 /// Note that, unlike most intrinsics, this is safe to call;
888 /// it does not require an `unsafe` block.
889 /// Therefore, implementations must not require the user to uphold
890 /// any safety invariants.
891 #[rustc_const_unstable(feature = "const_intrinsic_forget", issue = "none")]
892 pub fn forget<T: ?Sized>(_: T);
894 /// Reinterprets the bits of a value of one type as another type.
896 /// Both types must have the same size. Neither the original, nor the result,
897 /// may be an [invalid value](../../nomicon/what-unsafe-does.html).
899 /// `transmute` is semantically equivalent to a bitwise move of one type
900 /// into another. It copies the bits from the source value into the
901 /// destination value, then forgets the original. It's equivalent to C's
902 /// `memcpy` under the hood, just like `transmute_copy`.
904 /// Because `transmute` is a by-value operation, alignment of the *transmuted values
905 /// themselves* is not a concern. As with any other function, the compiler already ensures
906 /// both `T` and `U` are properly aligned. However, when transmuting values that *point
907 /// elsewhere* (such as pointers, references, boxes…), the caller has to ensure proper
908 /// alignment of the pointed-to values.
910 /// `transmute` is **incredibly** unsafe. There are a vast number of ways to
911 /// cause [undefined behavior][ub] with this function. `transmute` should be
912 /// the absolute last resort.
914 /// The [nomicon](../../nomicon/transmutes.html) has additional
917 /// [ub]: ../../reference/behavior-considered-undefined.html
921 /// There are a few things that `transmute` is really useful for.
923 /// Turning a pointer into a function pointer. This is *not* portable to
924 /// machines where function pointers and data pointers have different sizes.
927 /// fn foo() -> i32 {
930 /// let pointer = foo as *const ();
931 /// let function = unsafe {
932 /// std::mem::transmute::<*const (), fn() -> i32>(pointer)
934 /// assert_eq!(function(), 0);
937 /// Extending a lifetime, or shortening an invariant lifetime. This is
938 /// advanced, very unsafe Rust!
941 /// struct R<'a>(&'a i32);
942 /// unsafe fn extend_lifetime<'b>(r: R<'b>) -> R<'static> {
943 /// std::mem::transmute::<R<'b>, R<'static>>(r)
946 /// unsafe fn shorten_invariant_lifetime<'b, 'c>(r: &'b mut R<'static>)
947 /// -> &'b mut R<'c> {
948 /// std::mem::transmute::<&'b mut R<'static>, &'b mut R<'c>>(r)
954 /// Don't despair: many uses of `transmute` can be achieved through other means.
955 /// Below are common applications of `transmute` which can be replaced with safer
958 /// Turning raw bytes(`&[u8]`) to `u32`, `f64`, etc.:
961 /// let raw_bytes = [0x78, 0x56, 0x34, 0x12];
963 /// let num = unsafe {
964 /// std::mem::transmute::<[u8; 4], u32>(raw_bytes)
967 /// // use `u32::from_ne_bytes` instead
968 /// let num = u32::from_ne_bytes(raw_bytes);
969 /// // or use `u32::from_le_bytes` or `u32::from_be_bytes` to specify the endianness
970 /// let num = u32::from_le_bytes(raw_bytes);
971 /// assert_eq!(num, 0x12345678);
972 /// let num = u32::from_be_bytes(raw_bytes);
973 /// assert_eq!(num, 0x78563412);
976 /// Turning a pointer into a `usize`:
980 /// let ptr_num_transmute = unsafe {
981 /// std::mem::transmute::<&i32, usize>(ptr)
984 /// // Use an `as` cast instead
985 /// let ptr_num_cast = ptr as *const i32 as usize;
988 /// Turning a `*mut T` into an `&mut T`:
991 /// let ptr: *mut i32 = &mut 0;
992 /// let ref_transmuted = unsafe {
993 /// std::mem::transmute::<*mut i32, &mut i32>(ptr)
996 /// // Use a reborrow instead
997 /// let ref_casted = unsafe { &mut *ptr };
1000 /// Turning an `&mut T` into an `&mut U`:
1003 /// let ptr = &mut 0;
1004 /// let val_transmuted = unsafe {
1005 /// std::mem::transmute::<&mut i32, &mut u32>(ptr)
1008 /// // Now, put together `as` and reborrowing - note the chaining of `as`
1009 /// // `as` is not transitive
1010 /// let val_casts = unsafe { &mut *(ptr as *mut i32 as *mut u32) };
1013 /// Turning an `&str` into an `&[u8]`:
1016 /// // this is not a good way to do this.
1017 /// let slice = unsafe { std::mem::transmute::<&str, &[u8]>("Rust") };
1018 /// assert_eq!(slice, &[82, 117, 115, 116]);
1020 /// // You could use `str::as_bytes`
1021 /// let slice = "Rust".as_bytes();
1022 /// assert_eq!(slice, &[82, 117, 115, 116]);
1024 /// // Or, just use a byte string, if you have control over the string
1026 /// assert_eq!(b"Rust", &[82, 117, 115, 116]);
1029 /// Turning a `Vec<&T>` into a `Vec<Option<&T>>`.
1031 /// To transmute the inner type of the contents of a container, you must make sure to not
1032 /// violate any of the container's invariants. For `Vec`, this means that both the size
1033 /// *and alignment* of the inner types have to match. Other containers might rely on the
1034 /// size of the type, alignment, or even the `TypeId`, in which case transmuting wouldn't
1035 /// be possible at all without violating the container invariants.
1038 /// let store = [0, 1, 2, 3];
1039 /// let v_orig = store.iter().collect::<Vec<&i32>>();
1041 /// // clone the vector as we will reuse them later
1042 /// let v_clone = v_orig.clone();
1044 /// // Using transmute: this relies on the unspecified data layout of `Vec`, which is a
1045 /// // bad idea and could cause Undefined Behavior.
1046 /// // However, it is no-copy.
1047 /// let v_transmuted = unsafe {
1048 /// std::mem::transmute::<Vec<&i32>, Vec<Option<&i32>>>(v_clone)
1051 /// let v_clone = v_orig.clone();
1053 /// // This is the suggested, safe way.
1054 /// // It does copy the entire vector, though, into a new array.
1055 /// let v_collected = v_clone.into_iter()
1057 /// .collect::<Vec<Option<&i32>>>();
1059 /// let v_clone = v_orig.clone();
1061 /// // This is the proper no-copy, unsafe way of "transmuting" a `Vec`, without relying on the
1062 /// // data layout. Instead of literally calling `transmute`, we perform a pointer cast, but
1063 /// // in terms of converting the original inner type (`&i32`) to the new one (`Option<&i32>`),
1064 /// // this has all the same caveats. Besides the information provided above, also consult the
1065 /// // [`from_raw_parts`] documentation.
1066 /// let v_from_raw = unsafe {
1067 // FIXME Update this when vec_into_raw_parts is stabilized
1068 /// // Ensure the original vector is not dropped.
1069 /// let mut v_clone = std::mem::ManuallyDrop::new(v_clone);
1070 /// Vec::from_raw_parts(v_clone.as_mut_ptr() as *mut Option<&i32>,
1072 /// v_clone.capacity())
1076 /// [`from_raw_parts`]: ../../std/vec/struct.Vec.html#method.from_raw_parts
1078 /// Implementing `split_at_mut`:
1081 /// use std::{slice, mem};
1083 /// // There are multiple ways to do this, and there are multiple problems
1084 /// // with the following (transmute) way.
1085 /// fn split_at_mut_transmute<T>(slice: &mut [T], mid: usize)
1086 /// -> (&mut [T], &mut [T]) {
1087 /// let len = slice.len();
1088 /// assert!(mid <= len);
1090 /// let slice2 = mem::transmute::<&mut [T], &mut [T]>(slice);
1091 /// // first: transmute is not type safe; all it checks is that T and
1092 /// // U are of the same size. Second, right here, you have two
1093 /// // mutable references pointing to the same memory.
1094 /// (&mut slice[0..mid], &mut slice2[mid..len])
1098 /// // This gets rid of the type safety problems; `&mut *` will *only* give
1099 /// // you an `&mut T` from an `&mut T` or `*mut T`.
1100 /// fn split_at_mut_casts<T>(slice: &mut [T], mid: usize)
1101 /// -> (&mut [T], &mut [T]) {
1102 /// let len = slice.len();
1103 /// assert!(mid <= len);
1105 /// let slice2 = &mut *(slice as *mut [T]);
1106 /// // however, you still have two mutable references pointing to
1107 /// // the same memory.
1108 /// (&mut slice[0..mid], &mut slice2[mid..len])
1112 /// // This is how the standard library does it. This is the best method, if
1113 /// // you need to do something like this
1114 /// fn split_at_stdlib<T>(slice: &mut [T], mid: usize)
1115 /// -> (&mut [T], &mut [T]) {
1116 /// let len = slice.len();
1117 /// assert!(mid <= len);
1119 /// let ptr = slice.as_mut_ptr();
1120 /// // This now has three mutable references pointing at the same
1121 /// // memory. `slice`, the rvalue ret.0, and the rvalue ret.1.
1122 /// // `slice` is never used after `let ptr = ...`, and so one can
1123 /// // treat it as "dead", and therefore, you only have two real
1124 /// // mutable slices.
1125 /// (slice::from_raw_parts_mut(ptr, mid),
1126 /// slice::from_raw_parts_mut(ptr.add(mid), len - mid))
1130 #[stable(feature = "rust1", since = "1.0.0")]
1131 // NOTE: While this makes the intrinsic const stable, we have some custom code in const fn
1132 // checks that prevent its use within `const fn`.
1133 #[rustc_const_stable(feature = "const_transmute", since = "1.46.0")]
1134 #[rustc_diagnostic_item = "transmute"]
1135 pub fn transmute<T, U>(e: T) -> U;
1137 /// Returns `true` if the actual type given as `T` requires drop
1138 /// glue; returns `false` if the actual type provided for `T`
1139 /// implements `Copy`.
1141 /// If the actual type neither requires drop glue nor implements
1142 /// `Copy`, then the return value of this function is unspecified.
1144 /// Note that, unlike most intrinsics, this is safe to call;
1145 /// it does not require an `unsafe` block.
1146 /// Therefore, implementations must not require the user to uphold
1147 /// any safety invariants.
1149 /// The stabilized version of this intrinsic is [`mem::needs_drop`](crate::mem::needs_drop).
1150 #[rustc_const_stable(feature = "const_needs_drop", since = "1.40.0")]
1151 pub fn needs_drop<T>() -> bool;
1153 /// Calculates the offset from a pointer.
1155 /// This is implemented as an intrinsic to avoid converting to and from an
1156 /// integer, since the conversion would throw away aliasing information.
1160 /// Both the starting and resulting pointer must be either in bounds or one
1161 /// byte past the end of an allocated object. If either pointer is out of
1162 /// bounds or arithmetic overflow occurs then any further use of the
1163 /// returned value will result in undefined behavior.
1165 /// The stabilized version of this intrinsic is [`pointer::offset`].
1166 #[must_use = "returns a new pointer rather than modifying its argument"]
1167 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
1168 pub fn offset<T>(dst: *const T, offset: isize) -> *const T;
1170 /// Calculates the offset from a pointer, potentially wrapping.
1172 /// This is implemented as an intrinsic to avoid converting to and from an
1173 /// integer, since the conversion inhibits certain optimizations.
1177 /// Unlike the `offset` intrinsic, this intrinsic does not restrict the
1178 /// resulting pointer to point into or one byte past the end of an allocated
1179 /// object, and it wraps with two's complement arithmetic. The resulting
1180 /// value is not necessarily valid to be used to actually access memory.
1182 /// The stabilized version of this intrinsic is [`pointer::wrapping_offset`].
1183 #[must_use = "returns a new pointer rather than modifying its argument"]
1184 #[rustc_const_unstable(feature = "const_ptr_offset", issue = "71499")]
1185 pub fn arith_offset<T>(dst: *const T, offset: isize) -> *const T;
1187 /// Equivalent to the appropriate `llvm.memcpy.p0i8.0i8.*` intrinsic, with
1188 /// a size of `count` * `size_of::<T>()` and an alignment of
1189 /// `min_align_of::<T>()`
1191 /// The volatile parameter is set to `true`, so it will not be optimized out
1192 /// unless size is equal to zero.
1194 /// This intrinsic does not have a stable counterpart.
1195 pub fn volatile_copy_nonoverlapping_memory<T>(dst: *mut T, src: *const T, count: usize);
1196 /// Equivalent to the appropriate `llvm.memmove.p0i8.0i8.*` intrinsic, with
1197 /// a size of `count * size_of::<T>()` and an alignment of
1198 /// `min_align_of::<T>()`
1200 /// The volatile parameter is set to `true`, so it will not be optimized out
1201 /// unless size is equal to zero.
1203 /// This intrinsic does not have a stable counterpart.
1204 pub fn volatile_copy_memory<T>(dst: *mut T, src: *const T, count: usize);
1205 /// Equivalent to the appropriate `llvm.memset.p0i8.*` intrinsic, with a
1206 /// size of `count * size_of::<T>()` and an alignment of
1207 /// `min_align_of::<T>()`.
1209 /// The volatile parameter is set to `true`, so it will not be optimized out
1210 /// unless size is equal to zero.
1212 /// This intrinsic does not have a stable counterpart.
1213 pub fn volatile_set_memory<T>(dst: *mut T, val: u8, count: usize);
1215 /// Performs a volatile load from the `src` pointer.
1217 /// The stabilized version of this intrinsic is [`core::ptr::read_volatile`].
1218 pub fn volatile_load<T>(src: *const T) -> T;
1219 /// Performs a volatile store to the `dst` pointer.
1221 /// The stabilized version of this intrinsic is [`core::ptr::write_volatile`].
1222 pub fn volatile_store<T>(dst: *mut T, val: T);
1224 /// Performs a volatile load from the `src` pointer
1225 /// The pointer is not required to be aligned.
1227 /// This intrinsic does not have a stable counterpart.
1228 pub fn unaligned_volatile_load<T>(src: *const T) -> T;
1229 /// Performs a volatile store to the `dst` pointer.
1230 /// The pointer is not required to be aligned.
1232 /// This intrinsic does not have a stable counterpart.
1233 pub fn unaligned_volatile_store<T>(dst: *mut T, val: T);
1235 /// Returns the square root of an `f32`
1237 /// The stabilized version of this intrinsic is
1238 /// [`f32::sqrt`](../../std/primitive.f32.html#method.sqrt)
1239 pub fn sqrtf32(x: f32) -> f32;
1240 /// Returns the square root of an `f64`
1242 /// The stabilized version of this intrinsic is
1243 /// [`f64::sqrt`](../../std/primitive.f64.html#method.sqrt)
1244 pub fn sqrtf64(x: f64) -> f64;
1246 /// Raises an `f32` to an integer power.
1248 /// The stabilized version of this intrinsic is
1249 /// [`f32::powi`](../../std/primitive.f32.html#method.powi)
1250 pub fn powif32(a: f32, x: i32) -> f32;
1251 /// Raises an `f64` to an integer power.
1253 /// The stabilized version of this intrinsic is
1254 /// [`f64::powi`](../../std/primitive.f64.html#method.powi)
1255 pub fn powif64(a: f64, x: i32) -> f64;
1257 /// Returns the sine of an `f32`.
1259 /// The stabilized version of this intrinsic is
1260 /// [`f32::sin`](../../std/primitive.f32.html#method.sin)
1261 pub fn sinf32(x: f32) -> f32;
1262 /// Returns the sine of an `f64`.
1264 /// The stabilized version of this intrinsic is
1265 /// [`f64::sin`](../../std/primitive.f64.html#method.sin)
1266 pub fn sinf64(x: f64) -> f64;
1268 /// Returns the cosine of an `f32`.
1270 /// The stabilized version of this intrinsic is
1271 /// [`f32::cos`](../../std/primitive.f32.html#method.cos)
1272 pub fn cosf32(x: f32) -> f32;
1273 /// Returns the cosine of an `f64`.
1275 /// The stabilized version of this intrinsic is
1276 /// [`f64::cos`](../../std/primitive.f64.html#method.cos)
1277 pub fn cosf64(x: f64) -> f64;
1279 /// Raises an `f32` to an `f32` power.
1281 /// The stabilized version of this intrinsic is
1282 /// [`f32::powf`](../../std/primitive.f32.html#method.powf)
1283 pub fn powf32(a: f32, x: f32) -> f32;
1284 /// Raises an `f64` to an `f64` power.
1286 /// The stabilized version of this intrinsic is
1287 /// [`f64::powf`](../../std/primitive.f64.html#method.powf)
1288 pub fn powf64(a: f64, x: f64) -> f64;
1290 /// Returns the exponential of an `f32`.
1292 /// The stabilized version of this intrinsic is
1293 /// [`f32::exp`](../../std/primitive.f32.html#method.exp)
1294 pub fn expf32(x: f32) -> f32;
1295 /// Returns the exponential of an `f64`.
1297 /// The stabilized version of this intrinsic is
1298 /// [`f64::exp`](../../std/primitive.f64.html#method.exp)
1299 pub fn expf64(x: f64) -> f64;
1301 /// Returns 2 raised to the power of an `f32`.
1303 /// The stabilized version of this intrinsic is
1304 /// [`f32::exp2`](../../std/primitive.f32.html#method.exp2)
1305 pub fn exp2f32(x: f32) -> f32;
1306 /// Returns 2 raised to the power of an `f64`.
1308 /// The stabilized version of this intrinsic is
1309 /// [`f64::exp2`](../../std/primitive.f64.html#method.exp2)
1310 pub fn exp2f64(x: f64) -> f64;
1312 /// Returns the natural logarithm of an `f32`.
1314 /// The stabilized version of this intrinsic is
1315 /// [`f32::ln`](../../std/primitive.f32.html#method.ln)
1316 pub fn logf32(x: f32) -> f32;
1317 /// Returns the natural logarithm of an `f64`.
1319 /// The stabilized version of this intrinsic is
1320 /// [`f64::ln`](../../std/primitive.f64.html#method.ln)
1321 pub fn logf64(x: f64) -> f64;
1323 /// Returns the base 10 logarithm of an `f32`.
1325 /// The stabilized version of this intrinsic is
1326 /// [`f32::log10`](../../std/primitive.f32.html#method.log10)
1327 pub fn log10f32(x: f32) -> f32;
1328 /// Returns the base 10 logarithm of an `f64`.
1330 /// The stabilized version of this intrinsic is
1331 /// [`f64::log10`](../../std/primitive.f64.html#method.log10)
1332 pub fn log10f64(x: f64) -> f64;
1334 /// Returns the base 2 logarithm of an `f32`.
1336 /// The stabilized version of this intrinsic is
1337 /// [`f32::log2`](../../std/primitive.f32.html#method.log2)
1338 pub fn log2f32(x: f32) -> f32;
1339 /// Returns the base 2 logarithm of an `f64`.
1341 /// The stabilized version of this intrinsic is
1342 /// [`f64::log2`](../../std/primitive.f64.html#method.log2)
1343 pub fn log2f64(x: f64) -> f64;
1345 /// Returns `a * b + c` for `f32` values.
1347 /// The stabilized version of this intrinsic is
1348 /// [`f32::mul_add`](../../std/primitive.f32.html#method.mul_add)
1349 pub fn fmaf32(a: f32, b: f32, c: f32) -> f32;
1350 /// Returns `a * b + c` for `f64` values.
1352 /// The stabilized version of this intrinsic is
1353 /// [`f64::mul_add`](../../std/primitive.f64.html#method.mul_add)
1354 pub fn fmaf64(a: f64, b: f64, c: f64) -> f64;
1356 /// Returns the absolute value of an `f32`.
1358 /// The stabilized version of this intrinsic is
1359 /// [`f32::abs`](../../std/primitive.f32.html#method.abs)
1360 pub fn fabsf32(x: f32) -> f32;
1361 /// Returns the absolute value of an `f64`.
1363 /// The stabilized version of this intrinsic is
1364 /// [`f64::abs`](../../std/primitive.f64.html#method.abs)
1365 pub fn fabsf64(x: f64) -> f64;
1367 /// Returns the minimum of two `f32` values.
1369 /// Note that, unlike most intrinsics, this is safe to call;
1370 /// it does not require an `unsafe` block.
1371 /// Therefore, implementations must not require the user to uphold
1372 /// any safety invariants.
1374 /// The stabilized version of this intrinsic is
1376 pub fn minnumf32(x: f32, y: f32) -> f32;
1377 /// Returns the minimum of two `f64` values.
1379 /// Note that, unlike most intrinsics, this is safe to call;
1380 /// it does not require an `unsafe` block.
1381 /// Therefore, implementations must not require the user to uphold
1382 /// any safety invariants.
1384 /// The stabilized version of this intrinsic is
1386 pub fn minnumf64(x: f64, y: f64) -> f64;
1387 /// Returns the maximum of two `f32` values.
1389 /// Note that, unlike most intrinsics, this is safe to call;
1390 /// it does not require an `unsafe` block.
1391 /// Therefore, implementations must not require the user to uphold
1392 /// any safety invariants.
1394 /// The stabilized version of this intrinsic is
1396 pub fn maxnumf32(x: f32, y: f32) -> f32;
1397 /// Returns the maximum of two `f64` values.
1399 /// Note that, unlike most intrinsics, this is safe to call;
1400 /// it does not require an `unsafe` block.
1401 /// Therefore, implementations must not require the user to uphold
1402 /// any safety invariants.
1404 /// The stabilized version of this intrinsic is
1406 pub fn maxnumf64(x: f64, y: f64) -> f64;
1408 /// Copies the sign from `y` to `x` for `f32` values.
1410 /// The stabilized version of this intrinsic is
1411 /// [`f32::copysign`](../../std/primitive.f32.html#method.copysign)
1412 pub fn copysignf32(x: f32, y: f32) -> f32;
1413 /// Copies the sign from `y` to `x` for `f64` values.
1415 /// The stabilized version of this intrinsic is
1416 /// [`f64::copysign`](../../std/primitive.f64.html#method.copysign)
1417 pub fn copysignf64(x: f64, y: f64) -> f64;
1419 /// Returns the largest integer less than or equal to an `f32`.
1421 /// The stabilized version of this intrinsic is
1422 /// [`f32::floor`](../../std/primitive.f32.html#method.floor)
1423 pub fn floorf32(x: f32) -> f32;
1424 /// Returns the largest integer less than or equal to an `f64`.
1426 /// The stabilized version of this intrinsic is
1427 /// [`f64::floor`](../../std/primitive.f64.html#method.floor)
1428 pub fn floorf64(x: f64) -> f64;
1430 /// Returns the smallest integer greater than or equal to an `f32`.
1432 /// The stabilized version of this intrinsic is
1433 /// [`f32::ceil`](../../std/primitive.f32.html#method.ceil)
1434 pub fn ceilf32(x: f32) -> f32;
1435 /// Returns the smallest integer greater than or equal to an `f64`.
1437 /// The stabilized version of this intrinsic is
1438 /// [`f64::ceil`](../../std/primitive.f64.html#method.ceil)
1439 pub fn ceilf64(x: f64) -> f64;
1441 /// Returns the integer part of an `f32`.
1443 /// The stabilized version of this intrinsic is
1444 /// [`f32::trunc`](../../std/primitive.f32.html#method.trunc)
1445 pub fn truncf32(x: f32) -> f32;
1446 /// Returns the integer part of an `f64`.
1448 /// The stabilized version of this intrinsic is
1449 /// [`f64::trunc`](../../std/primitive.f64.html#method.trunc)
1450 pub fn truncf64(x: f64) -> f64;
1452 /// Returns the nearest integer to an `f32`. May raise an inexact floating-point exception
1453 /// if the argument is not an integer.
1454 pub fn rintf32(x: f32) -> f32;
1455 /// Returns the nearest integer to an `f64`. May raise an inexact floating-point exception
1456 /// if the argument is not an integer.
1457 pub fn rintf64(x: f64) -> f64;
1459 /// Returns the nearest integer to an `f32`.
1461 /// This intrinsic does not have a stable counterpart.
1462 pub fn nearbyintf32(x: f32) -> f32;
1463 /// Returns the nearest integer to an `f64`.
1465 /// This intrinsic does not have a stable counterpart.
1466 pub fn nearbyintf64(x: f64) -> f64;
1468 /// Returns the nearest integer to an `f32`. Rounds half-way cases away from zero.
1470 /// The stabilized version of this intrinsic is
1471 /// [`f32::round`](../../std/primitive.f32.html#method.round)
1472 pub fn roundf32(x: f32) -> f32;
1473 /// Returns the nearest integer to an `f64`. Rounds half-way cases away from zero.
1475 /// The stabilized version of this intrinsic is
1476 /// [`f64::round`](../../std/primitive.f64.html#method.round)
1477 pub fn roundf64(x: f64) -> f64;
1479 /// Float addition that allows optimizations based on algebraic rules.
1480 /// May assume inputs are finite.
1482 /// This intrinsic does not have a stable counterpart.
1483 pub fn fadd_fast<T: Copy>(a: T, b: T) -> T;
1485 /// Float subtraction that allows optimizations based on algebraic rules.
1486 /// May assume inputs are finite.
1488 /// This intrinsic does not have a stable counterpart.
1489 pub fn fsub_fast<T: Copy>(a: T, b: T) -> T;
1491 /// Float multiplication that allows optimizations based on algebraic rules.
1492 /// May assume inputs are finite.
1494 /// This intrinsic does not have a stable counterpart.
1495 pub fn fmul_fast<T: Copy>(a: T, b: T) -> T;
1497 /// Float division that allows optimizations based on algebraic rules.
1498 /// May assume inputs are finite.
1500 /// This intrinsic does not have a stable counterpart.
1501 pub fn fdiv_fast<T: Copy>(a: T, b: T) -> T;
1503 /// Float remainder that allows optimizations based on algebraic rules.
1504 /// May assume inputs are finite.
1506 /// This intrinsic does not have a stable counterpart.
1507 pub fn frem_fast<T: Copy>(a: T, b: T) -> T;
1509 /// Convert with LLVM’s fptoui/fptosi, which may return undef for values out of range
1510 /// (<https://github.com/rust-lang/rust/issues/10184>)
1512 /// Stabilized as [`f32::to_int_unchecked`] and [`f64::to_int_unchecked`].
1513 pub fn float_to_int_unchecked<Float: Copy, Int: Copy>(value: Float) -> Int;
1515 /// Returns the number of bits set in an integer type `T`
1517 /// Note that, unlike most intrinsics, this is safe to call;
1518 /// it does not require an `unsafe` block.
1519 /// Therefore, implementations must not require the user to uphold
1520 /// any safety invariants.
1522 /// The stabilized versions of this intrinsic are available on the integer
1523 /// primitives via the `count_ones` method. For example,
1524 /// [`u32::count_ones`]
1525 #[rustc_const_stable(feature = "const_ctpop", since = "1.40.0")]
1526 pub fn ctpop<T: Copy>(x: T) -> T;
1528 /// Returns the number of leading unset bits (zeroes) in an integer type `T`.
1530 /// Note that, unlike most intrinsics, this is safe to call;
1531 /// it does not require an `unsafe` block.
1532 /// Therefore, implementations must not require the user to uphold
1533 /// any safety invariants.
1535 /// The stabilized versions of this intrinsic are available on the integer
1536 /// primitives via the `leading_zeros` method. For example,
1537 /// [`u32::leading_zeros`]
1542 /// #![feature(core_intrinsics)]
1544 /// use std::intrinsics::ctlz;
1546 /// let x = 0b0001_1100_u8;
1547 /// let num_leading = ctlz(x);
1548 /// assert_eq!(num_leading, 3);
1551 /// An `x` with value `0` will return the bit width of `T`.
1554 /// #![feature(core_intrinsics)]
1556 /// use std::intrinsics::ctlz;
1559 /// let num_leading = ctlz(x);
1560 /// assert_eq!(num_leading, 16);
1562 #[rustc_const_stable(feature = "const_ctlz", since = "1.40.0")]
1563 pub fn ctlz<T: Copy>(x: T) -> T;
1565 /// Like `ctlz`, but extra-unsafe as it returns `undef` when
1566 /// given an `x` with value `0`.
1568 /// This intrinsic does not have a stable counterpart.
1573 /// #![feature(core_intrinsics)]
1575 /// use std::intrinsics::ctlz_nonzero;
1577 /// let x = 0b0001_1100_u8;
1578 /// let num_leading = unsafe { ctlz_nonzero(x) };
1579 /// assert_eq!(num_leading, 3);
1581 #[rustc_const_stable(feature = "constctlz", since = "1.50.0")]
1582 pub fn ctlz_nonzero<T: Copy>(x: T) -> T;
1584 /// Returns the number of trailing unset bits (zeroes) in an integer type `T`.
1586 /// Note that, unlike most intrinsics, this is safe to call;
1587 /// it does not require an `unsafe` block.
1588 /// Therefore, implementations must not require the user to uphold
1589 /// any safety invariants.
1591 /// The stabilized versions of this intrinsic are available on the integer
1592 /// primitives via the `trailing_zeros` method. For example,
1593 /// [`u32::trailing_zeros`]
1598 /// #![feature(core_intrinsics)]
1600 /// use std::intrinsics::cttz;
1602 /// let x = 0b0011_1000_u8;
1603 /// let num_trailing = cttz(x);
1604 /// assert_eq!(num_trailing, 3);
1607 /// An `x` with value `0` will return the bit width of `T`:
1610 /// #![feature(core_intrinsics)]
1612 /// use std::intrinsics::cttz;
1615 /// let num_trailing = cttz(x);
1616 /// assert_eq!(num_trailing, 16);
1618 #[rustc_const_stable(feature = "const_cttz", since = "1.40.0")]
1619 pub fn cttz<T: Copy>(x: T) -> T;
1621 /// Like `cttz`, but extra-unsafe as it returns `undef` when
1622 /// given an `x` with value `0`.
1624 /// This intrinsic does not have a stable counterpart.
1629 /// #![feature(core_intrinsics)]
1631 /// use std::intrinsics::cttz_nonzero;
1633 /// let x = 0b0011_1000_u8;
1634 /// let num_trailing = unsafe { cttz_nonzero(x) };
1635 /// assert_eq!(num_trailing, 3);
1637 #[rustc_const_stable(feature = "const_cttz", since = "1.53.0")]
1638 pub fn cttz_nonzero<T: Copy>(x: T) -> T;
1640 /// Reverses the bytes in an integer type `T`.
1642 /// Note that, unlike most intrinsics, this is safe to call;
1643 /// it does not require an `unsafe` block.
1644 /// Therefore, implementations must not require the user to uphold
1645 /// any safety invariants.
1647 /// The stabilized versions of this intrinsic are available on the integer
1648 /// primitives via the `swap_bytes` method. For example,
1649 /// [`u32::swap_bytes`]
1650 #[rustc_const_stable(feature = "const_bswap", since = "1.40.0")]
1651 pub fn bswap<T: Copy>(x: T) -> T;
1653 /// Reverses the bits in an integer type `T`.
1655 /// Note that, unlike most intrinsics, this is safe to call;
1656 /// it does not require an `unsafe` block.
1657 /// Therefore, implementations must not require the user to uphold
1658 /// any safety invariants.
1660 /// The stabilized versions of this intrinsic are available on the integer
1661 /// primitives via the `reverse_bits` method. For example,
1662 /// [`u32::reverse_bits`]
1663 #[rustc_const_stable(feature = "const_bitreverse", since = "1.40.0")]
1664 pub fn bitreverse<T: Copy>(x: T) -> T;
1666 /// Performs checked integer addition.
1668 /// Note that, unlike most intrinsics, this is safe to call;
1669 /// it does not require an `unsafe` block.
1670 /// Therefore, implementations must not require the user to uphold
1671 /// any safety invariants.
1673 /// The stabilized versions of this intrinsic are available on the integer
1674 /// primitives via the `overflowing_add` method. For example,
1675 /// [`u32::overflowing_add`]
1676 #[rustc_const_stable(feature = "const_int_overflow", since = "1.40.0")]
1677 pub fn add_with_overflow<T: Copy>(x: T, y: T) -> (T, bool);
1679 /// Performs checked integer subtraction
1681 /// Note that, unlike most intrinsics, this is safe to call;
1682 /// it does not require an `unsafe` block.
1683 /// Therefore, implementations must not require the user to uphold
1684 /// any safety invariants.
1686 /// The stabilized versions of this intrinsic are available on the integer
1687 /// primitives via the `overflowing_sub` method. For example,
1688 /// [`u32::overflowing_sub`]
1689 #[rustc_const_stable(feature = "const_int_overflow", since = "1.40.0")]
1690 pub fn sub_with_overflow<T: Copy>(x: T, y: T) -> (T, bool);
1692 /// Performs checked integer multiplication
1694 /// Note that, unlike most intrinsics, this is safe to call;
1695 /// it does not require an `unsafe` block.
1696 /// Therefore, implementations must not require the user to uphold
1697 /// any safety invariants.
1699 /// The stabilized versions of this intrinsic are available on the integer
1700 /// primitives via the `overflowing_mul` method. For example,
1701 /// [`u32::overflowing_mul`]
1702 #[rustc_const_stable(feature = "const_int_overflow", since = "1.40.0")]
1703 pub fn mul_with_overflow<T: Copy>(x: T, y: T) -> (T, bool);
1705 /// Performs an exact division, resulting in undefined behavior where
1706 /// `x % y != 0` or `y == 0` or `x == T::MIN && y == -1`
1708 /// This intrinsic does not have a stable counterpart.
1709 pub fn exact_div<T: Copy>(x: T, y: T) -> T;
1711 /// Performs an unchecked division, resulting in undefined behavior
1712 /// where `y == 0` or `x == T::MIN && y == -1`
1714 /// Safe wrappers for this intrinsic are available on the integer
1715 /// primitives via the `checked_div` method. For example,
1716 /// [`u32::checked_div`]
1717 #[rustc_const_stable(feature = "const_int_unchecked_arith", since = "1.52.0")]
1718 pub fn unchecked_div<T: Copy>(x: T, y: T) -> T;
1719 /// Returns the remainder of an unchecked division, resulting in
1720 /// undefined behavior when `y == 0` or `x == T::MIN && y == -1`
1722 /// Safe wrappers for this intrinsic are available on the integer
1723 /// primitives via the `checked_rem` method. For example,
1724 /// [`u32::checked_rem`]
1725 #[rustc_const_stable(feature = "const_int_unchecked_arith", since = "1.52.0")]
1726 pub fn unchecked_rem<T: Copy>(x: T, y: T) -> T;
1728 /// Performs an unchecked left shift, resulting in undefined behavior when
1729 /// `y < 0` or `y >= N`, where N is the width of T in bits.
1731 /// Safe wrappers for this intrinsic are available on the integer
1732 /// primitives via the `checked_shl` method. For example,
1733 /// [`u32::checked_shl`]
1734 #[rustc_const_stable(feature = "const_int_unchecked", since = "1.40.0")]
1735 pub fn unchecked_shl<T: Copy>(x: T, y: T) -> T;
1736 /// Performs an unchecked right shift, resulting in undefined behavior when
1737 /// `y < 0` or `y >= N`, where N is the width of T in bits.
1739 /// Safe wrappers for this intrinsic are available on the integer
1740 /// primitives via the `checked_shr` method. For example,
1741 /// [`u32::checked_shr`]
1742 #[rustc_const_stable(feature = "const_int_unchecked", since = "1.40.0")]
1743 pub fn unchecked_shr<T: Copy>(x: T, y: T) -> T;
1745 /// Returns the result of an unchecked addition, resulting in
1746 /// undefined behavior when `x + y > T::MAX` or `x + y < T::MIN`.
1748 /// This intrinsic does not have a stable counterpart.
1749 #[rustc_const_unstable(feature = "const_int_unchecked_arith", issue = "none")]
1750 pub fn unchecked_add<T: Copy>(x: T, y: T) -> T;
1752 /// Returns the result of an unchecked subtraction, resulting in
1753 /// undefined behavior when `x - y > T::MAX` or `x - y < T::MIN`.
1755 /// This intrinsic does not have a stable counterpart.
1756 #[rustc_const_unstable(feature = "const_int_unchecked_arith", issue = "none")]
1757 pub fn unchecked_sub<T: Copy>(x: T, y: T) -> T;
1759 /// Returns the result of an unchecked multiplication, 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_mul<T: Copy>(x: T, y: T) -> T;
1766 /// Performs rotate left.
1768 /// Note that, unlike most intrinsics, this is safe to call;
1769 /// it does not require an `unsafe` block.
1770 /// Therefore, implementations must not require the user to uphold
1771 /// any safety invariants.
1773 /// The stabilized versions of this intrinsic are available on the integer
1774 /// primitives via the `rotate_left` method. For example,
1775 /// [`u32::rotate_left`]
1776 #[rustc_const_stable(feature = "const_int_rotate", since = "1.40.0")]
1777 pub fn rotate_left<T: Copy>(x: T, y: T) -> T;
1779 /// Performs rotate right.
1781 /// Note that, unlike most intrinsics, this is safe to call;
1782 /// it does not require an `unsafe` block.
1783 /// Therefore, implementations must not require the user to uphold
1784 /// any safety invariants.
1786 /// The stabilized versions of this intrinsic are available on the integer
1787 /// primitives via the `rotate_right` method. For example,
1788 /// [`u32::rotate_right`]
1789 #[rustc_const_stable(feature = "const_int_rotate", since = "1.40.0")]
1790 pub fn rotate_right<T: Copy>(x: T, y: T) -> T;
1792 /// Returns (a + b) mod 2<sup>N</sup>, where N is the width of T in bits.
1794 /// Note that, unlike most intrinsics, this is safe to call;
1795 /// it does not require an `unsafe` block.
1796 /// Therefore, implementations must not require the user to uphold
1797 /// any safety invariants.
1799 /// The stabilized versions of this intrinsic are available on the integer
1800 /// primitives via the `wrapping_add` method. For example,
1801 /// [`u32::wrapping_add`]
1802 #[rustc_const_stable(feature = "const_int_wrapping", since = "1.40.0")]
1803 pub fn wrapping_add<T: Copy>(a: T, b: T) -> T;
1804 /// Returns (a - b) mod 2<sup>N</sup>, where N is the width of T in bits.
1806 /// Note that, unlike most intrinsics, this is safe to call;
1807 /// it does not require an `unsafe` block.
1808 /// Therefore, implementations must not require the user to uphold
1809 /// any safety invariants.
1811 /// The stabilized versions of this intrinsic are available on the integer
1812 /// primitives via the `wrapping_sub` method. For example,
1813 /// [`u32::wrapping_sub`]
1814 #[rustc_const_stable(feature = "const_int_wrapping", since = "1.40.0")]
1815 pub fn wrapping_sub<T: Copy>(a: T, b: T) -> T;
1816 /// Returns (a * b) mod 2<sup>N</sup>, where N is the width of T in bits.
1818 /// Note that, unlike most intrinsics, this is safe to call;
1819 /// it does not require an `unsafe` block.
1820 /// Therefore, implementations must not require the user to uphold
1821 /// any safety invariants.
1823 /// The stabilized versions of this intrinsic are available on the integer
1824 /// primitives via the `wrapping_mul` method. For example,
1825 /// [`u32::wrapping_mul`]
1826 #[rustc_const_stable(feature = "const_int_wrapping", since = "1.40.0")]
1827 pub fn wrapping_mul<T: Copy>(a: T, b: T) -> T;
1829 /// Computes `a + b`, saturating at numeric bounds.
1831 /// Note that, unlike most intrinsics, this is safe to call;
1832 /// it does not require an `unsafe` block.
1833 /// Therefore, implementations must not require the user to uphold
1834 /// any safety invariants.
1836 /// The stabilized versions of this intrinsic are available on the integer
1837 /// primitives via the `saturating_add` method. For example,
1838 /// [`u32::saturating_add`]
1839 #[rustc_const_stable(feature = "const_int_saturating", since = "1.40.0")]
1840 pub fn saturating_add<T: Copy>(a: T, b: T) -> T;
1841 /// Computes `a - b`, saturating at numeric bounds.
1843 /// Note that, unlike most intrinsics, this is safe to call;
1844 /// it does not require an `unsafe` block.
1845 /// Therefore, implementations must not require the user to uphold
1846 /// any safety invariants.
1848 /// The stabilized versions of this intrinsic are available on the integer
1849 /// primitives via the `saturating_sub` method. For example,
1850 /// [`u32::saturating_sub`]
1851 #[rustc_const_stable(feature = "const_int_saturating", since = "1.40.0")]
1852 pub fn saturating_sub<T: Copy>(a: T, b: T) -> T;
1854 /// Returns the value of the discriminant for the variant in 'v';
1855 /// if `T` has no discriminant, returns `0`.
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 version of this intrinsic is [`core::mem::discriminant`].
1863 #[rustc_const_unstable(feature = "const_discriminant", issue = "69821")]
1864 pub fn discriminant_value<T>(v: &T) -> <T as DiscriminantKind>::Discriminant;
1866 /// Returns the number of variants of the type `T` cast to a `usize`;
1867 /// if `T` has no variants, returns `0`. Uninhabited variants will be counted.
1869 /// Note that, unlike most intrinsics, this is safe to call;
1870 /// it does not require an `unsafe` block.
1871 /// Therefore, implementations must not require the user to uphold
1872 /// any safety invariants.
1874 /// The to-be-stabilized version of this intrinsic is [`mem::variant_count`].
1875 #[rustc_const_unstable(feature = "variant_count", issue = "73662")]
1876 pub fn variant_count<T>() -> usize;
1878 /// Rust's "try catch" construct which invokes the function pointer `try_fn`
1879 /// with the data pointer `data`.
1881 /// The third argument is a function called if a panic occurs. This function
1882 /// takes the data pointer and a pointer to the target-specific exception
1883 /// object that was caught. For more information see the compiler's
1884 /// source as well as std's catch implementation.
1885 pub fn r#try(try_fn: fn(*mut u8), data: *mut u8, catch_fn: fn(*mut u8, *mut u8)) -> i32;
1887 /// Emits a `!nontemporal` store according to LLVM (see their docs).
1888 /// Probably will never become stable.
1889 pub fn nontemporal_store<T>(ptr: *mut T, val: T);
1891 /// See documentation of `<*const T>::offset_from` for details.
1892 #[rustc_const_unstable(feature = "const_ptr_offset_from", issue = "41079")]
1893 pub fn ptr_offset_from<T>(ptr: *const T, base: *const T) -> isize;
1895 /// See documentation of `<*const T>::guaranteed_eq` for details.
1897 /// Note that, unlike most intrinsics, this is safe to call;
1898 /// it does not require an `unsafe` block.
1899 /// Therefore, implementations must not require the user to uphold
1900 /// any safety invariants.
1901 #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
1902 pub fn ptr_guaranteed_eq<T>(ptr: *const T, other: *const T) -> bool;
1904 /// See documentation of `<*const T>::guaranteed_ne` for details.
1906 /// Note that, unlike most intrinsics, this is safe to call;
1907 /// it does not require an `unsafe` block.
1908 /// Therefore, implementations must not require the user to uphold
1909 /// any safety invariants.
1910 #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
1911 pub fn ptr_guaranteed_ne<T>(ptr: *const T, other: *const T) -> bool;
1913 /// Allocate at compile time. Should not be called at runtime.
1914 #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
1915 pub fn const_allocate(size: usize, align: usize) -> *mut u8;
1917 /// Determines whether the raw bytes of the two values are equal.
1919 /// The is particularly handy for arrays, since it allows things like just
1920 /// comparing `i96`s instead of forcing `alloca`s for `[6 x i16]`.
1922 /// Above some backend-decided threshold this will emit calls to `memcmp`,
1923 /// like slice equality does, instead of causing massive code size.
1927 /// It's UB to call this if any of the *bytes* in `*a` or `*b` are uninitialized.
1928 /// Note that this is a stricter criterion than just the *values* being
1929 /// fully-initialized: if `T` has padding, it's UB to call this intrinsic.
1931 /// (The implementation is allowed to branch on the results of comparisons,
1932 /// which is UB if any of their inputs are `undef`.)
1933 #[cfg(not(bootstrap))]
1934 #[rustc_const_unstable(feature = "const_intrinsic_raw_eq", issue = "none")]
1935 pub fn raw_eq<T>(a: &T, b: &T) -> bool;
1938 // Some functions are defined here because they accidentally got made
1939 // available in this module on stable. See <https://github.com/rust-lang/rust/issues/15702>.
1940 // (`transmute` also falls into this category, but it cannot be wrapped due to the
1941 // check that `T` and `U` have the same size.)
1943 /// Checks whether `ptr` is properly aligned with respect to
1944 /// `align_of::<T>()`.
1945 pub(crate) fn is_aligned_and_not_null<T>(ptr: *const T) -> bool {
1946 !ptr.is_null() && ptr as usize % mem::align_of::<T>() == 0
1949 /// Copies `count * size_of::<T>()` bytes from `src` to `dst`. The source
1950 /// and destination must *not* overlap.
1952 /// For regions of memory which might overlap, use [`copy`] instead.
1954 /// `copy_nonoverlapping` is semantically equivalent to C's [`memcpy`], but
1955 /// with the argument order swapped.
1957 /// [`memcpy`]: https://en.cppreference.com/w/c/string/byte/memcpy
1961 /// Behavior is undefined if any of the following conditions are violated:
1963 /// * `src` must be [valid] for reads of `count * size_of::<T>()` bytes.
1965 /// * `dst` must be [valid] for writes of `count * size_of::<T>()` bytes.
1967 /// * Both `src` and `dst` must be properly aligned.
1969 /// * The region of memory beginning at `src` with a size of `count *
1970 /// size_of::<T>()` bytes must *not* overlap with the region of memory
1971 /// beginning at `dst` with the same size.
1973 /// Like [`read`], `copy_nonoverlapping` creates a bitwise copy of `T`, regardless of
1974 /// whether `T` is [`Copy`]. If `T` is not [`Copy`], using *both* the values
1975 /// in the region beginning at `*src` and the region beginning at `*dst` can
1976 /// [violate memory safety][read-ownership].
1978 /// Note that even if the effectively copied size (`count * size_of::<T>()`) is
1979 /// `0`, the pointers must be non-null and properly aligned.
1981 /// [`read`]: crate::ptr::read
1982 /// [read-ownership]: crate::ptr::read#ownership-of-the-returned-value
1983 /// [valid]: crate::ptr#safety
1987 /// Manually implement [`Vec::append`]:
1992 /// /// Moves all the elements of `src` into `dst`, leaving `src` empty.
1993 /// fn append<T>(dst: &mut Vec<T>, src: &mut Vec<T>) {
1994 /// let src_len = src.len();
1995 /// let dst_len = dst.len();
1997 /// // Ensure that `dst` has enough capacity to hold all of `src`.
1998 /// dst.reserve(src_len);
2001 /// // The call to offset is always safe because `Vec` will never
2002 /// // allocate more than `isize::MAX` bytes.
2003 /// let dst_ptr = dst.as_mut_ptr().offset(dst_len as isize);
2004 /// let src_ptr = src.as_ptr();
2006 /// // Truncate `src` without dropping its contents. We do this first,
2007 /// // to avoid problems in case something further down panics.
2010 /// // The two regions cannot overlap because mutable references do
2011 /// // not alias, and two different vectors cannot own the same
2013 /// ptr::copy_nonoverlapping(src_ptr, dst_ptr, src_len);
2015 /// // Notify `dst` that it now holds the contents of `src`.
2016 /// dst.set_len(dst_len + src_len);
2020 /// let mut a = vec!['r'];
2021 /// let mut b = vec!['u', 's', 't'];
2023 /// append(&mut a, &mut b);
2025 /// assert_eq!(a, &['r', 'u', 's', 't']);
2026 /// assert!(b.is_empty());
2029 /// [`Vec::append`]: ../../std/vec/struct.Vec.html#method.append
2030 #[doc(alias = "memcpy")]
2031 #[stable(feature = "rust1", since = "1.0.0")]
2032 #[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
2034 pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize) {
2035 extern "rust-intrinsic" {
2036 #[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
2037 pub fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
2040 // FIXME: Perform these checks only at run time
2041 /*if cfg!(debug_assertions)
2042 && !(is_aligned_and_not_null(src)
2043 && is_aligned_and_not_null(dst)
2044 && is_nonoverlapping(src, dst, count))
2046 // Not panicking to keep codegen impact smaller.
2050 // SAFETY: the safety contract for `copy_nonoverlapping` must be
2051 // upheld by the caller.
2052 unsafe { copy_nonoverlapping(src, dst, count) }
2055 /// Copies `count * size_of::<T>()` bytes from `src` to `dst`. The source
2056 /// and destination may overlap.
2058 /// If the source and destination will *never* overlap,
2059 /// [`copy_nonoverlapping`] can be used instead.
2061 /// `copy` is semantically equivalent to C's [`memmove`], but with the argument
2062 /// order swapped. Copying takes place as if the bytes were copied from `src`
2063 /// to a temporary array and then copied from the array to `dst`.
2065 /// [`memmove`]: https://en.cppreference.com/w/c/string/byte/memmove
2069 /// Behavior is undefined if any of the following conditions are violated:
2071 /// * `src` must be [valid] for reads of `count * size_of::<T>()` bytes.
2073 /// * `dst` must be [valid] for writes of `count * size_of::<T>()` bytes.
2075 /// * Both `src` and `dst` must be properly aligned.
2077 /// Like [`read`], `copy` creates a bitwise copy of `T`, regardless of
2078 /// whether `T` is [`Copy`]. If `T` is not [`Copy`], using both the values
2079 /// in the region beginning at `*src` and the region beginning at `*dst` can
2080 /// [violate memory safety][read-ownership].
2082 /// Note that even if the effectively copied size (`count * size_of::<T>()`) is
2083 /// `0`, the pointers must be non-null and properly aligned.
2085 /// [`read`]: crate::ptr::read
2086 /// [read-ownership]: crate::ptr::read#ownership-of-the-returned-value
2087 /// [valid]: crate::ptr#safety
2091 /// Efficiently create a Rust vector from an unsafe buffer:
2098 /// /// * `ptr` must be correctly aligned for its type and non-zero.
2099 /// /// * `ptr` must be valid for reads of `elts` contiguous elements of type `T`.
2100 /// /// * Those elements must not be used after calling this function unless `T: Copy`.
2101 /// # #[allow(dead_code)]
2102 /// unsafe fn from_buf_raw<T>(ptr: *const T, elts: usize) -> Vec<T> {
2103 /// let mut dst = Vec::with_capacity(elts);
2105 /// // SAFETY: Our precondition ensures the source is aligned and valid,
2106 /// // and `Vec::with_capacity` ensures that we have usable space to write them.
2107 /// ptr::copy(ptr, dst.as_mut_ptr(), elts);
2109 /// // SAFETY: We created it with this much capacity earlier,
2110 /// // and the previous `copy` has initialized these elements.
2111 /// dst.set_len(elts);
2115 #[doc(alias = "memmove")]
2116 #[stable(feature = "rust1", since = "1.0.0")]
2117 #[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
2119 pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
2120 extern "rust-intrinsic" {
2121 #[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
2122 fn copy<T>(src: *const T, dst: *mut T, count: usize);
2125 // FIXME: Perform these checks only at run time
2126 /*if cfg!(debug_assertions) && !(is_aligned_and_not_null(src) && is_aligned_and_not_null(dst)) {
2127 // Not panicking to keep codegen impact smaller.
2131 // SAFETY: the safety contract for `copy` must be upheld by the caller.
2132 unsafe { copy(src, dst, count) }
2135 /// Sets `count * size_of::<T>()` bytes of memory starting at `dst` to
2138 /// `write_bytes` is similar to C's [`memset`], but sets `count *
2139 /// size_of::<T>()` bytes to `val`.
2141 /// [`memset`]: https://en.cppreference.com/w/c/string/byte/memset
2145 /// Behavior is undefined if any of the following conditions are violated:
2147 /// * `dst` must be [valid] for writes of `count * size_of::<T>()` bytes.
2149 /// * `dst` must be properly aligned.
2151 /// Additionally, the caller must ensure that writing `count *
2152 /// size_of::<T>()` bytes to the given region of memory results in a valid
2153 /// value of `T`. Using a region of memory typed as a `T` that contains an
2154 /// invalid value of `T` is undefined behavior.
2156 /// Note that even if the effectively copied size (`count * size_of::<T>()`) is
2157 /// `0`, the pointer must be non-null and properly aligned.
2159 /// [valid]: crate::ptr#safety
2168 /// let mut vec = vec![0u32; 4];
2170 /// let vec_ptr = vec.as_mut_ptr();
2171 /// ptr::write_bytes(vec_ptr, 0xfe, 2);
2173 /// assert_eq!(vec, [0xfefefefe, 0xfefefefe, 0, 0]);
2176 /// Creating an invalid value:
2181 /// let mut v = Box::new(0i32);
2184 /// // Leaks the previously held value by overwriting the `Box<T>` with
2185 /// // a null pointer.
2186 /// ptr::write_bytes(&mut v as *mut Box<i32>, 0, 1);
2189 /// // At this point, using or dropping `v` results in undefined behavior.
2190 /// // drop(v); // ERROR
2192 /// // Even leaking `v` "uses" it, and hence is undefined behavior.
2193 /// // mem::forget(v); // ERROR
2195 /// // In fact, `v` is invalid according to basic type layout invariants, so *any*
2196 /// // operation touching it is undefined behavior.
2197 /// // let v2 = v; // ERROR
2200 /// // Let us instead put in a valid value
2201 /// ptr::write(&mut v as *mut Box<i32>, Box::new(42i32));
2204 /// // Now the box is fine
2205 /// assert_eq!(*v, 42);
2207 #[stable(feature = "rust1", since = "1.0.0")]
2209 pub unsafe fn write_bytes<T>(dst: *mut T, val: u8, count: usize) {
2210 extern "rust-intrinsic" {
2211 fn write_bytes<T>(dst: *mut T, val: u8, count: usize);
2214 debug_assert!(is_aligned_and_not_null(dst), "attempt to write to unaligned or null pointer");
2216 // SAFETY: the safety contract for `write_bytes` must be upheld by the caller.
2217 unsafe { write_bytes(dst, val, count) }