1 //! Compiler intrinsics.
3 //! The corresponding definitions are in `librustc_codegen_llvm/intrinsic.rs`.
7 //! The volatile intrinsics provide operations intended to act on I/O
8 //! memory, which are guaranteed to not be reordered by the compiler
9 //! across other volatile intrinsics. See the LLVM documentation on
12 //! [volatile]: http://llvm.org/docs/LangRef.html#volatile-memory-accesses
16 //! The atomic intrinsics provide common atomic operations on machine
17 //! words, with multiple possible memory orderings. They obey the same
18 //! semantics as C++11. See the LLVM documentation on [[atomics]].
20 //! [atomics]: http://llvm.org/docs/Atomics.html
22 //! A quick refresher on memory ordering:
24 //! * Acquire - a barrier for acquiring a lock. Subsequent reads and writes
25 //! take place after the barrier.
26 //! * Release - a barrier for releasing a lock. Preceding reads and writes
27 //! take place before the barrier.
28 //! * Sequentially consistent - sequentially consistent operations are
29 //! guaranteed to happen in order. This is the standard mode for working
30 //! with atomic types and is equivalent to Java's `volatile`.
32 #![unstable(feature = "core_intrinsics",
33 reason = "intrinsics are unlikely to ever be stabilized, instead \
34 they should be used through stabilized interfaces \
35 in the rest of the standard library",
37 #![allow(missing_docs)]
39 #[stable(feature = "drop_in_place", since = "1.8.0")]
40 #[rustc_deprecated(reason = "no longer an intrinsic - use `ptr::drop_in_place` directly",
42 pub use ptr::drop_in_place;
44 extern "rust-intrinsic" {
45 // N.B., these intrinsics take raw pointers because they mutate aliased
46 // memory, which is not valid for either `&` or `&mut`.
48 /// Stores a value if the current value is the same as the `old` value.
49 /// The stabilized version of this intrinsic is available on the
50 /// `std::sync::atomic` types via the `compare_exchange` method by passing
51 /// [`Ordering::SeqCst`](../../std/sync/atomic/enum.Ordering.html)
52 /// as both the `success` and `failure` parameters. For example,
53 /// [`AtomicBool::compare_exchange`][compare_exchange].
55 /// [compare_exchange]: ../../std/sync/atomic/struct.AtomicBool.html#method.compare_exchange
56 pub fn atomic_cxchg<T>(dst: *mut T, old: T, src: T) -> (T, bool);
57 /// Stores a value if the current value is the same as the `old` value.
58 /// The stabilized version of this intrinsic is available on the
59 /// `std::sync::atomic` types via the `compare_exchange` method by passing
60 /// [`Ordering::Acquire`](../../std/sync/atomic/enum.Ordering.html)
61 /// as both the `success` and `failure` parameters. For example,
62 /// [`AtomicBool::compare_exchange`][compare_exchange].
64 /// [compare_exchange]: ../../std/sync/atomic/struct.AtomicBool.html#method.compare_exchange
65 pub fn atomic_cxchg_acq<T>(dst: *mut T, old: T, src: T) -> (T, bool);
66 /// Stores a value if the current value is the same as the `old` value.
67 /// The stabilized version of this intrinsic is available on the
68 /// `std::sync::atomic` types via the `compare_exchange` method by passing
69 /// [`Ordering::Release`](../../std/sync/atomic/enum.Ordering.html)
70 /// as the `success` and
71 /// [`Ordering::Relaxed`](../../std/sync/atomic/enum.Ordering.html)
72 /// as the `failure` parameters. For example,
73 /// [`AtomicBool::compare_exchange`][compare_exchange].
75 /// [compare_exchange]: ../../std/sync/atomic/struct.AtomicBool.html#method.compare_exchange
76 pub fn atomic_cxchg_rel<T>(dst: *mut T, old: T, src: T) -> (T, bool);
77 /// Stores a value if the current value is the same as the `old` value.
78 /// The stabilized version of this intrinsic is available on the
79 /// `std::sync::atomic` types via the `compare_exchange` method by passing
80 /// [`Ordering::AcqRel`](../../std/sync/atomic/enum.Ordering.html)
81 /// as the `success` and
82 /// [`Ordering::Acquire`](../../std/sync/atomic/enum.Ordering.html)
83 /// as the `failure` parameters. For example,
84 /// [`AtomicBool::compare_exchange`][compare_exchange].
86 /// [compare_exchange]: ../../std/sync/atomic/struct.AtomicBool.html#method.compare_exchange
87 pub fn atomic_cxchg_acqrel<T>(dst: *mut T, old: T, src: T) -> (T, bool);
88 /// 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 /// `std::sync::atomic` types via the `compare_exchange` method by passing
91 /// [`Ordering::Relaxed`](../../std/sync/atomic/enum.Ordering.html)
92 /// as both the `success` and `failure` parameters. For example,
93 /// [`AtomicBool::compare_exchange`][compare_exchange].
95 /// [compare_exchange]: ../../std/sync/atomic/struct.AtomicBool.html#method.compare_exchange
96 pub fn atomic_cxchg_relaxed<T>(dst: *mut T, old: T, src: T) -> (T, bool);
97 /// Stores a value if the current value is the same as the `old` value.
98 /// The stabilized version of this intrinsic is available on the
99 /// `std::sync::atomic` types via the `compare_exchange` method by passing
100 /// [`Ordering::SeqCst`](../../std/sync/atomic/enum.Ordering.html)
101 /// as the `success` and
102 /// [`Ordering::Relaxed`](../../std/sync/atomic/enum.Ordering.html)
103 /// as the `failure` parameters. For example,
104 /// [`AtomicBool::compare_exchange`][compare_exchange].
106 /// [compare_exchange]: ../../std/sync/atomic/struct.AtomicBool.html#method.compare_exchange
107 pub fn atomic_cxchg_failrelaxed<T>(dst: *mut T, old: T, src: T) -> (T, bool);
108 /// Stores a value if the current value is the same as the `old` value.
109 /// The stabilized version of this intrinsic is available on the
110 /// `std::sync::atomic` types via the `compare_exchange` method by passing
111 /// [`Ordering::SeqCst`](../../std/sync/atomic/enum.Ordering.html)
112 /// as the `success` and
113 /// [`Ordering::Acquire`](../../std/sync/atomic/enum.Ordering.html)
114 /// as the `failure` parameters. For example,
115 /// [`AtomicBool::compare_exchange`][compare_exchange].
117 /// [compare_exchange]: ../../std/sync/atomic/struct.AtomicBool.html#method.compare_exchange
118 pub fn atomic_cxchg_failacq<T>(dst: *mut T, old: T, src: T) -> (T, bool);
119 /// Stores a value if the current value is the same as the `old` value.
120 /// The stabilized version of this intrinsic is available on the
121 /// `std::sync::atomic` types via the `compare_exchange` method by passing
122 /// [`Ordering::Acquire`](../../std/sync/atomic/enum.Ordering.html)
123 /// as the `success` and
124 /// [`Ordering::Relaxed`](../../std/sync/atomic/enum.Ordering.html)
125 /// as the `failure` parameters. For example,
126 /// [`AtomicBool::compare_exchange`][compare_exchange].
128 /// [compare_exchange]: ../../std/sync/atomic/struct.AtomicBool.html#method.compare_exchange
129 pub fn atomic_cxchg_acq_failrelaxed<T>(dst: *mut T, old: T, src: T) -> (T, bool);
130 /// 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 /// `std::sync::atomic` types via the `compare_exchange` method by passing
133 /// [`Ordering::AcqRel`](../../std/sync/atomic/enum.Ordering.html)
134 /// as the `success` and
135 /// [`Ordering::Relaxed`](../../std/sync/atomic/enum.Ordering.html)
136 /// as the `failure` parameters. For example,
137 /// [`AtomicBool::compare_exchange`][compare_exchange].
139 /// [compare_exchange]: ../../std/sync/atomic/struct.AtomicBool.html#method.compare_exchange
140 pub fn atomic_cxchg_acqrel_failrelaxed<T>(dst: *mut T, old: T, src: T) -> (T, bool);
142 /// Stores a value if the current value is the same as the `old` value.
143 /// The stabilized version of this intrinsic is available on the
144 /// `std::sync::atomic` types via the `compare_exchange_weak` method by passing
145 /// [`Ordering::SeqCst`](../../std/sync/atomic/enum.Ordering.html)
146 /// as both the `success` and `failure` parameters. For example,
147 /// [`AtomicBool::compare_exchange_weak`][cew].
149 /// [cew]: ../../std/sync/atomic/struct.AtomicBool.html#method.compare_exchange_weak
150 pub fn atomic_cxchgweak<T>(dst: *mut T, old: T, src: T) -> (T, bool);
151 /// Stores a value if the current value is the same as the `old` value.
152 /// The stabilized version of this intrinsic is available on the
153 /// `std::sync::atomic` types via the `compare_exchange_weak` method by passing
154 /// [`Ordering::Acquire`](../../std/sync/atomic/enum.Ordering.html)
155 /// as both the `success` and `failure` parameters. For example,
156 /// [`AtomicBool::compare_exchange_weak`][cew].
158 /// [cew]: ../../std/sync/atomic/struct.AtomicBool.html#method.compare_exchange_weak
159 pub fn atomic_cxchgweak_acq<T>(dst: *mut T, old: T, src: T) -> (T, bool);
160 /// Stores a value if the current value is the same as the `old` value.
161 /// The stabilized version of this intrinsic is available on the
162 /// `std::sync::atomic` types via the `compare_exchange_weak` method by passing
163 /// [`Ordering::Release`](../../std/sync/atomic/enum.Ordering.html)
164 /// as the `success` and
165 /// [`Ordering::Relaxed`](../../std/sync/atomic/enum.Ordering.html)
166 /// as the `failure` parameters. For example,
167 /// [`AtomicBool::compare_exchange_weak`][cew].
169 /// [cew]: ../../std/sync/atomic/struct.AtomicBool.html#method.compare_exchange_weak
170 pub fn atomic_cxchgweak_rel<T>(dst: *mut T, old: T, src: T) -> (T, bool);
171 /// Stores a value if the current value is the same as the `old` value.
172 /// The stabilized version of this intrinsic is available on the
173 /// `std::sync::atomic` types via the `compare_exchange_weak` method by passing
174 /// [`Ordering::AcqRel`](../../std/sync/atomic/enum.Ordering.html)
175 /// as the `success` and
176 /// [`Ordering::Acquire`](../../std/sync/atomic/enum.Ordering.html)
177 /// as the `failure` parameters. For example,
178 /// [`AtomicBool::compare_exchange_weak`][cew].
180 /// [cew]: ../../std/sync/atomic/struct.AtomicBool.html#method.compare_exchange_weak
181 pub fn atomic_cxchgweak_acqrel<T>(dst: *mut T, old: T, src: T) -> (T, bool);
182 /// Stores a value if the current value is the same as the `old` value.
183 /// The stabilized version of this intrinsic is available on the
184 /// `std::sync::atomic` types via the `compare_exchange_weak` method by passing
185 /// [`Ordering::Relaxed`](../../std/sync/atomic/enum.Ordering.html)
186 /// as both the `success` and `failure` parameters. For example,
187 /// [`AtomicBool::compare_exchange_weak`][cew].
189 /// [cew]: ../../std/sync/atomic/struct.AtomicBool.html#method.compare_exchange_weak
190 pub fn atomic_cxchgweak_relaxed<T>(dst: *mut T, old: T, src: T) -> (T, bool);
191 /// Stores a value if the current value is the same as the `old` value.
192 /// The stabilized version of this intrinsic is available on the
193 /// `std::sync::atomic` types via the `compare_exchange_weak` method by passing
194 /// [`Ordering::SeqCst`](../../std/sync/atomic/enum.Ordering.html)
195 /// as the `success` and
196 /// [`Ordering::Relaxed`](../../std/sync/atomic/enum.Ordering.html)
197 /// as the `failure` parameters. For example,
198 /// [`AtomicBool::compare_exchange_weak`][cew].
200 /// [cew]: ../../std/sync/atomic/struct.AtomicBool.html#method.compare_exchange_weak
201 pub fn atomic_cxchgweak_failrelaxed<T>(dst: *mut T, old: T, src: T) -> (T, bool);
202 /// Stores a value if the current value is the same as the `old` value.
203 /// The stabilized version of this intrinsic is available on the
204 /// `std::sync::atomic` types via the `compare_exchange_weak` method by passing
205 /// [`Ordering::SeqCst`](../../std/sync/atomic/enum.Ordering.html)
206 /// as the `success` and
207 /// [`Ordering::Acquire`](../../std/sync/atomic/enum.Ordering.html)
208 /// as the `failure` parameters. For example,
209 /// [`AtomicBool::compare_exchange_weak`][cew].
211 /// [cew]: ../../std/sync/atomic/struct.AtomicBool.html#method.compare_exchange_weak
212 pub fn atomic_cxchgweak_failacq<T>(dst: *mut T, old: T, src: T) -> (T, bool);
213 /// Stores a value if the current value is the same as the `old` value.
214 /// The stabilized version of this intrinsic is available on the
215 /// `std::sync::atomic` types via the `compare_exchange_weak` method by passing
216 /// [`Ordering::Acquire`](../../std/sync/atomic/enum.Ordering.html)
217 /// as the `success` and
218 /// [`Ordering::Relaxed`](../../std/sync/atomic/enum.Ordering.html)
219 /// as the `failure` parameters. For example,
220 /// [`AtomicBool::compare_exchange_weak`][cew].
222 /// [cew]: ../../std/sync/atomic/struct.AtomicBool.html#method.compare_exchange_weak
223 pub fn atomic_cxchgweak_acq_failrelaxed<T>(dst: *mut T, old: T, src: T) -> (T, bool);
224 /// Stores a value if the current value is the same as the `old` value.
225 /// The stabilized version of this intrinsic is available on the
226 /// `std::sync::atomic` types via the `compare_exchange_weak` method by passing
227 /// [`Ordering::AcqRel`](../../std/sync/atomic/enum.Ordering.html)
228 /// as the `success` and
229 /// [`Ordering::Relaxed`](../../std/sync/atomic/enum.Ordering.html)
230 /// as the `failure` parameters. For example,
231 /// [`AtomicBool::compare_exchange_weak`][cew].
233 /// [cew]: ../../std/sync/atomic/struct.AtomicBool.html#method.compare_exchange_weak
234 pub fn atomic_cxchgweak_acqrel_failrelaxed<T>(dst: *mut T, old: T, src: T) -> (T, bool);
236 /// Loads the current value of the pointer.
237 /// The stabilized version of this intrinsic is available on the
238 /// `std::sync::atomic` types via the `load` method by passing
239 /// [`Ordering::SeqCst`](../../std/sync/atomic/enum.Ordering.html)
240 /// as the `order`. For example,
241 /// [`AtomicBool::load`](../../std/sync/atomic/struct.AtomicBool.html#method.load).
242 pub fn atomic_load<T>(src: *const T) -> T;
243 /// Loads the current value of the pointer.
244 /// The stabilized version of this intrinsic is available on the
245 /// `std::sync::atomic` types via the `load` method by passing
246 /// [`Ordering::Acquire`](../../std/sync/atomic/enum.Ordering.html)
247 /// as the `order`. For example,
248 /// [`AtomicBool::load`](../../std/sync/atomic/struct.AtomicBool.html#method.load).
249 pub fn atomic_load_acq<T>(src: *const T) -> T;
250 /// Loads the current value of the pointer.
251 /// The stabilized version of this intrinsic is available on the
252 /// `std::sync::atomic` types via the `load` method by passing
253 /// [`Ordering::Relaxed`](../../std/sync/atomic/enum.Ordering.html)
254 /// as the `order`. For example,
255 /// [`AtomicBool::load`](../../std/sync/atomic/struct.AtomicBool.html#method.load).
256 pub fn atomic_load_relaxed<T>(src: *const T) -> T;
257 pub fn atomic_load_unordered<T>(src: *const T) -> T;
259 /// Stores the value at the specified memory location.
260 /// The stabilized version of this intrinsic is available on the
261 /// `std::sync::atomic` types via the `store` method by passing
262 /// [`Ordering::SeqCst`](../../std/sync/atomic/enum.Ordering.html)
263 /// as the `order`. For example,
264 /// [`AtomicBool::store`](../../std/sync/atomic/struct.AtomicBool.html#method.store).
265 pub fn atomic_store<T>(dst: *mut T, val: T);
266 /// Stores the value at the specified memory location.
267 /// The stabilized version of this intrinsic is available on the
268 /// `std::sync::atomic` types via the `store` method by passing
269 /// [`Ordering::Release`](../../std/sync/atomic/enum.Ordering.html)
270 /// as the `order`. For example,
271 /// [`AtomicBool::store`](../../std/sync/atomic/struct.AtomicBool.html#method.store).
272 pub fn atomic_store_rel<T>(dst: *mut T, val: T);
273 /// Stores the value at the specified memory location.
274 /// The stabilized version of this intrinsic is available on the
275 /// `std::sync::atomic` types via the `store` method by passing
276 /// [`Ordering::Relaxed`](../../std/sync/atomic/enum.Ordering.html)
277 /// as the `order`. For example,
278 /// [`AtomicBool::store`](../../std/sync/atomic/struct.AtomicBool.html#method.store).
279 pub fn atomic_store_relaxed<T>(dst: *mut T, val: T);
280 pub fn atomic_store_unordered<T>(dst: *mut T, val: T);
282 /// Stores the value at the specified memory location, returning the old value.
283 /// The stabilized version of this intrinsic is available on the
284 /// `std::sync::atomic` types via the `swap` method by passing
285 /// [`Ordering::SeqCst`](../../std/sync/atomic/enum.Ordering.html)
286 /// as the `order`. For example,
287 /// [`AtomicBool::swap`](../../std/sync/atomic/struct.AtomicBool.html#method.swap).
288 pub fn atomic_xchg<T>(dst: *mut T, src: T) -> T;
289 /// Stores the value at the specified memory location, returning the old value.
290 /// The stabilized version of this intrinsic is available on the
291 /// `std::sync::atomic` types via the `swap` method by passing
292 /// [`Ordering::Acquire`](../../std/sync/atomic/enum.Ordering.html)
293 /// as the `order`. For example,
294 /// [`AtomicBool::swap`](../../std/sync/atomic/struct.AtomicBool.html#method.swap).
295 pub fn atomic_xchg_acq<T>(dst: *mut T, src: T) -> T;
296 /// Stores the value at the specified memory location, returning the old value.
297 /// The stabilized version of this intrinsic is available on the
298 /// `std::sync::atomic` types via the `swap` method by passing
299 /// [`Ordering::Release`](../../std/sync/atomic/enum.Ordering.html)
300 /// as the `order`. For example,
301 /// [`AtomicBool::swap`](../../std/sync/atomic/struct.AtomicBool.html#method.swap).
302 pub fn atomic_xchg_rel<T>(dst: *mut T, src: T) -> T;
303 /// Stores the value at the specified memory location, returning the old value.
304 /// The stabilized version of this intrinsic is available on the
305 /// `std::sync::atomic` types via the `swap` method by passing
306 /// [`Ordering::AcqRel`](../../std/sync/atomic/enum.Ordering.html)
307 /// as the `order`. For example,
308 /// [`AtomicBool::swap`](../../std/sync/atomic/struct.AtomicBool.html#method.swap).
309 pub fn atomic_xchg_acqrel<T>(dst: *mut T, src: T) -> T;
310 /// Stores the value at the specified memory location, returning the old value.
311 /// The stabilized version of this intrinsic is available on the
312 /// `std::sync::atomic` types via the `swap` method by passing
313 /// [`Ordering::Relaxed`](../../std/sync/atomic/enum.Ordering.html)
314 /// as the `order`. For example,
315 /// [`AtomicBool::swap`](../../std/sync/atomic/struct.AtomicBool.html#method.swap).
316 pub fn atomic_xchg_relaxed<T>(dst: *mut T, src: T) -> T;
318 /// Adds to the current value, returning the previous value.
319 /// The stabilized version of this intrinsic is available on the
320 /// `std::sync::atomic` types via the `fetch_add` method by passing
321 /// [`Ordering::SeqCst`](../../std/sync/atomic/enum.Ordering.html)
322 /// as the `order`. For example,
323 /// [`AtomicIsize::fetch_add`](../../std/sync/atomic/struct.AtomicIsize.html#method.fetch_add).
324 pub fn atomic_xadd<T>(dst: *mut T, src: T) -> T;
325 /// Adds to the current value, returning the previous value.
326 /// The stabilized version of this intrinsic is available on the
327 /// `std::sync::atomic` types via the `fetch_add` method by passing
328 /// [`Ordering::Acquire`](../../std/sync/atomic/enum.Ordering.html)
329 /// as the `order`. For example,
330 /// [`AtomicIsize::fetch_add`](../../std/sync/atomic/struct.AtomicIsize.html#method.fetch_add).
331 pub fn atomic_xadd_acq<T>(dst: *mut T, src: T) -> T;
332 /// Adds to the current value, returning the previous value.
333 /// The stabilized version of this intrinsic is available on the
334 /// `std::sync::atomic` types via the `fetch_add` method by passing
335 /// [`Ordering::Release`](../../std/sync/atomic/enum.Ordering.html)
336 /// as the `order`. For example,
337 /// [`AtomicIsize::fetch_add`](../../std/sync/atomic/struct.AtomicIsize.html#method.fetch_add).
338 pub fn atomic_xadd_rel<T>(dst: *mut T, src: T) -> T;
339 /// Adds to the current value, returning the previous value.
340 /// The stabilized version of this intrinsic is available on the
341 /// `std::sync::atomic` types via the `fetch_add` method by passing
342 /// [`Ordering::AcqRel`](../../std/sync/atomic/enum.Ordering.html)
343 /// as the `order`. For example,
344 /// [`AtomicIsize::fetch_add`](../../std/sync/atomic/struct.AtomicIsize.html#method.fetch_add).
345 pub fn atomic_xadd_acqrel<T>(dst: *mut T, src: T) -> T;
346 /// Adds to the current value, returning the previous value.
347 /// The stabilized version of this intrinsic is available on the
348 /// `std::sync::atomic` types via the `fetch_add` method by passing
349 /// [`Ordering::Relaxed`](../../std/sync/atomic/enum.Ordering.html)
350 /// as the `order`. For example,
351 /// [`AtomicIsize::fetch_add`](../../std/sync/atomic/struct.AtomicIsize.html#method.fetch_add).
352 pub fn atomic_xadd_relaxed<T>(dst: *mut T, src: T) -> T;
354 /// Subtract from the current value, returning the previous value.
355 /// The stabilized version of this intrinsic is available on the
356 /// `std::sync::atomic` types via the `fetch_sub` method by passing
357 /// [`Ordering::SeqCst`](../../std/sync/atomic/enum.Ordering.html)
358 /// as the `order`. For example,
359 /// [`AtomicIsize::fetch_sub`](../../std/sync/atomic/struct.AtomicIsize.html#method.fetch_sub).
360 pub fn atomic_xsub<T>(dst: *mut T, src: T) -> T;
361 /// Subtract from the current value, returning the previous value.
362 /// The stabilized version of this intrinsic is available on the
363 /// `std::sync::atomic` types via the `fetch_sub` method by passing
364 /// [`Ordering::Acquire`](../../std/sync/atomic/enum.Ordering.html)
365 /// as the `order`. For example,
366 /// [`AtomicIsize::fetch_sub`](../../std/sync/atomic/struct.AtomicIsize.html#method.fetch_sub).
367 pub fn atomic_xsub_acq<T>(dst: *mut T, src: T) -> T;
368 /// Subtract from the current value, returning the previous value.
369 /// The stabilized version of this intrinsic is available on the
370 /// `std::sync::atomic` types via the `fetch_sub` method by passing
371 /// [`Ordering::Release`](../../std/sync/atomic/enum.Ordering.html)
372 /// as the `order`. For example,
373 /// [`AtomicIsize::fetch_sub`](../../std/sync/atomic/struct.AtomicIsize.html#method.fetch_sub).
374 pub fn atomic_xsub_rel<T>(dst: *mut T, src: T) -> T;
375 /// Subtract from the current value, returning the previous value.
376 /// The stabilized version of this intrinsic is available on the
377 /// `std::sync::atomic` types via the `fetch_sub` method by passing
378 /// [`Ordering::AcqRel`](../../std/sync/atomic/enum.Ordering.html)
379 /// as the `order`. For example,
380 /// [`AtomicIsize::fetch_sub`](../../std/sync/atomic/struct.AtomicIsize.html#method.fetch_sub).
381 pub fn atomic_xsub_acqrel<T>(dst: *mut T, src: T) -> T;
382 /// Subtract from the current value, returning the previous value.
383 /// The stabilized version of this intrinsic is available on the
384 /// `std::sync::atomic` types via the `fetch_sub` method by passing
385 /// [`Ordering::Relaxed`](../../std/sync/atomic/enum.Ordering.html)
386 /// as the `order`. For example,
387 /// [`AtomicIsize::fetch_sub`](../../std/sync/atomic/struct.AtomicIsize.html#method.fetch_sub).
388 pub fn atomic_xsub_relaxed<T>(dst: *mut T, src: T) -> T;
390 /// Bitwise and with the current value, returning the previous value.
391 /// The stabilized version of this intrinsic is available on the
392 /// `std::sync::atomic` types via the `fetch_and` method by passing
393 /// [`Ordering::SeqCst`](../../std/sync/atomic/enum.Ordering.html)
394 /// as the `order`. For example,
395 /// [`AtomicBool::fetch_and`](../../std/sync/atomic/struct.AtomicBool.html#method.fetch_and).
396 pub fn atomic_and<T>(dst: *mut T, src: T) -> T;
397 /// Bitwise and with the current value, returning the previous value.
398 /// The stabilized version of this intrinsic is available on the
399 /// `std::sync::atomic` types via the `fetch_and` method by passing
400 /// [`Ordering::Acquire`](../../std/sync/atomic/enum.Ordering.html)
401 /// as the `order`. For example,
402 /// [`AtomicBool::fetch_and`](../../std/sync/atomic/struct.AtomicBool.html#method.fetch_and).
403 pub fn atomic_and_acq<T>(dst: *mut T, src: T) -> T;
404 /// Bitwise and with the current value, returning the previous value.
405 /// The stabilized version of this intrinsic is available on the
406 /// `std::sync::atomic` types via the `fetch_and` method by passing
407 /// [`Ordering::Release`](../../std/sync/atomic/enum.Ordering.html)
408 /// as the `order`. For example,
409 /// [`AtomicBool::fetch_and`](../../std/sync/atomic/struct.AtomicBool.html#method.fetch_and).
410 pub fn atomic_and_rel<T>(dst: *mut T, src: T) -> T;
411 /// Bitwise and with the current value, returning the previous value.
412 /// The stabilized version of this intrinsic is available on the
413 /// `std::sync::atomic` types via the `fetch_and` method by passing
414 /// [`Ordering::AcqRel`](../../std/sync/atomic/enum.Ordering.html)
415 /// as the `order`. For example,
416 /// [`AtomicBool::fetch_and`](../../std/sync/atomic/struct.AtomicBool.html#method.fetch_and).
417 pub fn atomic_and_acqrel<T>(dst: *mut T, src: T) -> T;
418 /// Bitwise and with the current value, returning the previous value.
419 /// The stabilized version of this intrinsic is available on the
420 /// `std::sync::atomic` types via the `fetch_and` method by passing
421 /// [`Ordering::Relaxed`](../../std/sync/atomic/enum.Ordering.html)
422 /// as the `order`. For example,
423 /// [`AtomicBool::fetch_and`](../../std/sync/atomic/struct.AtomicBool.html#method.fetch_and).
424 pub fn atomic_and_relaxed<T>(dst: *mut T, src: T) -> T;
426 /// Bitwise nand with the current value, returning the previous value.
427 /// The stabilized version of this intrinsic is available on the
428 /// `std::sync::atomic::AtomicBool` type via the `fetch_nand` method by passing
429 /// [`Ordering::SeqCst`](../../std/sync/atomic/enum.Ordering.html)
430 /// as the `order`. For example,
431 /// [`AtomicBool::fetch_nand`](../../std/sync/atomic/struct.AtomicBool.html#method.fetch_nand).
432 pub fn atomic_nand<T>(dst: *mut T, src: T) -> T;
433 /// Bitwise nand with the current value, returning the previous value.
434 /// The stabilized version of this intrinsic is available on the
435 /// `std::sync::atomic::AtomicBool` type via the `fetch_nand` method by passing
436 /// [`Ordering::Acquire`](../../std/sync/atomic/enum.Ordering.html)
437 /// as the `order`. For example,
438 /// [`AtomicBool::fetch_nand`](../../std/sync/atomic/struct.AtomicBool.html#method.fetch_nand).
439 pub fn atomic_nand_acq<T>(dst: *mut T, src: T) -> T;
440 /// Bitwise nand with the current value, returning the previous value.
441 /// The stabilized version of this intrinsic is available on the
442 /// `std::sync::atomic::AtomicBool` type via the `fetch_nand` method by passing
443 /// [`Ordering::Release`](../../std/sync/atomic/enum.Ordering.html)
444 /// as the `order`. For example,
445 /// [`AtomicBool::fetch_nand`](../../std/sync/atomic/struct.AtomicBool.html#method.fetch_nand).
446 pub fn atomic_nand_rel<T>(dst: *mut T, src: T) -> T;
447 /// Bitwise nand with the current value, returning the previous value.
448 /// The stabilized version of this intrinsic is available on the
449 /// `std::sync::atomic::AtomicBool` type via the `fetch_nand` method by passing
450 /// [`Ordering::AcqRel`](../../std/sync/atomic/enum.Ordering.html)
451 /// as the `order`. For example,
452 /// [`AtomicBool::fetch_nand`](../../std/sync/atomic/struct.AtomicBool.html#method.fetch_nand).
453 pub fn atomic_nand_acqrel<T>(dst: *mut T, src: T) -> T;
454 /// Bitwise nand with the current value, returning the previous value.
455 /// The stabilized version of this intrinsic is available on the
456 /// `std::sync::atomic::AtomicBool` type via the `fetch_nand` method by passing
457 /// [`Ordering::Relaxed`](../../std/sync/atomic/enum.Ordering.html)
458 /// as the `order`. For example,
459 /// [`AtomicBool::fetch_nand`](../../std/sync/atomic/struct.AtomicBool.html#method.fetch_nand).
460 pub fn atomic_nand_relaxed<T>(dst: *mut T, src: T) -> T;
462 /// Bitwise or with the current value, returning the previous value.
463 /// The stabilized version of this intrinsic is available on the
464 /// `std::sync::atomic` types via the `fetch_or` method by passing
465 /// [`Ordering::SeqCst`](../../std/sync/atomic/enum.Ordering.html)
466 /// as the `order`. For example,
467 /// [`AtomicBool::fetch_or`](../../std/sync/atomic/struct.AtomicBool.html#method.fetch_or).
468 pub fn atomic_or<T>(dst: *mut T, src: T) -> T;
469 /// Bitwise or with the current value, returning the previous value.
470 /// The stabilized version of this intrinsic is available on the
471 /// `std::sync::atomic` types via the `fetch_or` method by passing
472 /// [`Ordering::Acquire`](../../std/sync/atomic/enum.Ordering.html)
473 /// as the `order`. For example,
474 /// [`AtomicBool::fetch_or`](../../std/sync/atomic/struct.AtomicBool.html#method.fetch_or).
475 pub fn atomic_or_acq<T>(dst: *mut T, src: T) -> T;
476 /// Bitwise or with the current value, returning the previous value.
477 /// The stabilized version of this intrinsic is available on the
478 /// `std::sync::atomic` types via the `fetch_or` method by passing
479 /// [`Ordering::Release`](../../std/sync/atomic/enum.Ordering.html)
480 /// as the `order`. For example,
481 /// [`AtomicBool::fetch_or`](../../std/sync/atomic/struct.AtomicBool.html#method.fetch_or).
482 pub fn atomic_or_rel<T>(dst: *mut T, src: T) -> T;
483 /// Bitwise or with the current value, returning the previous value.
484 /// The stabilized version of this intrinsic is available on the
485 /// `std::sync::atomic` types via the `fetch_or` method by passing
486 /// [`Ordering::AcqRel`](../../std/sync/atomic/enum.Ordering.html)
487 /// as the `order`. For example,
488 /// [`AtomicBool::fetch_or`](../../std/sync/atomic/struct.AtomicBool.html#method.fetch_or).
489 pub fn atomic_or_acqrel<T>(dst: *mut T, src: T) -> T;
490 /// Bitwise or with the current value, returning the previous value.
491 /// The stabilized version of this intrinsic is available on the
492 /// `std::sync::atomic` types via the `fetch_or` method by passing
493 /// [`Ordering::Relaxed`](../../std/sync/atomic/enum.Ordering.html)
494 /// as the `order`. For example,
495 /// [`AtomicBool::fetch_or`](../../std/sync/atomic/struct.AtomicBool.html#method.fetch_or).
496 pub fn atomic_or_relaxed<T>(dst: *mut T, src: T) -> T;
498 /// Bitwise xor with the current value, returning the previous value.
499 /// The stabilized version of this intrinsic is available on the
500 /// `std::sync::atomic` types via the `fetch_xor` method by passing
501 /// [`Ordering::SeqCst`](../../std/sync/atomic/enum.Ordering.html)
502 /// as the `order`. For example,
503 /// [`AtomicBool::fetch_xor`](../../std/sync/atomic/struct.AtomicBool.html#method.fetch_xor).
504 pub fn atomic_xor<T>(dst: *mut T, src: T) -> T;
505 /// Bitwise xor with the current value, returning the previous value.
506 /// The stabilized version of this intrinsic is available on the
507 /// `std::sync::atomic` types via the `fetch_xor` method by passing
508 /// [`Ordering::Acquire`](../../std/sync/atomic/enum.Ordering.html)
509 /// as the `order`. For example,
510 /// [`AtomicBool::fetch_xor`](../../std/sync/atomic/struct.AtomicBool.html#method.fetch_xor).
511 pub fn atomic_xor_acq<T>(dst: *mut T, src: T) -> T;
512 /// Bitwise xor with the current value, returning the previous value.
513 /// The stabilized version of this intrinsic is available on the
514 /// `std::sync::atomic` types via the `fetch_xor` method by passing
515 /// [`Ordering::Release`](../../std/sync/atomic/enum.Ordering.html)
516 /// as the `order`. For example,
517 /// [`AtomicBool::fetch_xor`](../../std/sync/atomic/struct.AtomicBool.html#method.fetch_xor).
518 pub fn atomic_xor_rel<T>(dst: *mut T, src: T) -> T;
519 /// Bitwise xor with the current value, returning the previous value.
520 /// The stabilized version of this intrinsic is available on the
521 /// `std::sync::atomic` types via the `fetch_xor` method by passing
522 /// [`Ordering::AcqRel`](../../std/sync/atomic/enum.Ordering.html)
523 /// as the `order`. For example,
524 /// [`AtomicBool::fetch_xor`](../../std/sync/atomic/struct.AtomicBool.html#method.fetch_xor).
525 pub fn atomic_xor_acqrel<T>(dst: *mut T, src: T) -> T;
526 /// Bitwise xor with the current value, returning the previous value.
527 /// The stabilized version of this intrinsic is available on the
528 /// `std::sync::atomic` types via the `fetch_xor` method by passing
529 /// [`Ordering::Relaxed`](../../std/sync/atomic/enum.Ordering.html)
530 /// as the `order`. For example,
531 /// [`AtomicBool::fetch_xor`](../../std/sync/atomic/struct.AtomicBool.html#method.fetch_xor).
532 pub fn atomic_xor_relaxed<T>(dst: *mut T, src: T) -> T;
534 pub fn atomic_max<T>(dst: *mut T, src: T) -> T;
535 pub fn atomic_max_acq<T>(dst: *mut T, src: T) -> T;
536 pub fn atomic_max_rel<T>(dst: *mut T, src: T) -> T;
537 pub fn atomic_max_acqrel<T>(dst: *mut T, src: T) -> T;
538 pub fn atomic_max_relaxed<T>(dst: *mut T, src: T) -> T;
540 pub fn atomic_min<T>(dst: *mut T, src: T) -> T;
541 pub fn atomic_min_acq<T>(dst: *mut T, src: T) -> T;
542 pub fn atomic_min_rel<T>(dst: *mut T, src: T) -> T;
543 pub fn atomic_min_acqrel<T>(dst: *mut T, src: T) -> T;
544 pub fn atomic_min_relaxed<T>(dst: *mut T, src: T) -> T;
546 pub fn atomic_umin<T>(dst: *mut T, src: T) -> T;
547 pub fn atomic_umin_acq<T>(dst: *mut T, src: T) -> T;
548 pub fn atomic_umin_rel<T>(dst: *mut T, src: T) -> T;
549 pub fn atomic_umin_acqrel<T>(dst: *mut T, src: T) -> T;
550 pub fn atomic_umin_relaxed<T>(dst: *mut T, src: T) -> T;
552 pub fn atomic_umax<T>(dst: *mut T, src: T) -> T;
553 pub fn atomic_umax_acq<T>(dst: *mut T, src: T) -> T;
554 pub fn atomic_umax_rel<T>(dst: *mut T, src: T) -> T;
555 pub fn atomic_umax_acqrel<T>(dst: *mut T, src: T) -> T;
556 pub fn atomic_umax_relaxed<T>(dst: *mut T, src: T) -> T;
558 /// The `prefetch` intrinsic is a hint to the code generator to insert a prefetch instruction
559 /// if supported; otherwise, it is a no-op.
560 /// Prefetches have no effect on the behavior of the program but can change its performance
563 /// The `locality` argument must be a constant integer and is a temporal locality specifier
564 /// ranging from (0) - no locality, to (3) - extremely local keep in cache
565 pub fn prefetch_read_data<T>(data: *const T, locality: i32);
566 /// The `prefetch` intrinsic is a hint to the code generator to insert a prefetch instruction
567 /// if supported; otherwise, it is a no-op.
568 /// Prefetches have no effect on the behavior of the program but can change its performance
571 /// The `locality` argument must be a constant integer and is a temporal locality specifier
572 /// ranging from (0) - no locality, to (3) - extremely local keep in cache
573 pub fn prefetch_write_data<T>(data: *const T, locality: i32);
574 /// The `prefetch` intrinsic is a hint to the code generator to insert a prefetch instruction
575 /// if supported; otherwise, it is a no-op.
576 /// Prefetches have no effect on the behavior of the program but can change its performance
579 /// The `locality` argument must be a constant integer and is a temporal locality specifier
580 /// ranging from (0) - no locality, to (3) - extremely local keep in cache
581 pub fn prefetch_read_instruction<T>(data: *const T, locality: i32);
582 /// The `prefetch` intrinsic is a hint to the code generator to insert a prefetch instruction
583 /// if supported; otherwise, it is a no-op.
584 /// Prefetches have no effect on the behavior of the program but can change its performance
587 /// The `locality` argument must be a constant integer and is a temporal locality specifier
588 /// ranging from (0) - no locality, to (3) - extremely local keep in cache
589 pub fn prefetch_write_instruction<T>(data: *const T, locality: i32);
592 extern "rust-intrinsic" {
594 pub fn atomic_fence();
595 pub fn atomic_fence_acq();
596 pub fn atomic_fence_rel();
597 pub fn atomic_fence_acqrel();
599 /// A compiler-only memory barrier.
601 /// Memory accesses will never be reordered across this barrier by the
602 /// compiler, but no instructions will be emitted for it. This is
603 /// appropriate for operations on the same thread that may be preempted,
604 /// such as when interacting with signal handlers.
605 pub fn atomic_singlethreadfence();
606 pub fn atomic_singlethreadfence_acq();
607 pub fn atomic_singlethreadfence_rel();
608 pub fn atomic_singlethreadfence_acqrel();
610 /// Magic intrinsic that derives its meaning from attributes
611 /// attached to the function.
613 /// For example, dataflow uses this to inject static assertions so
614 /// that `rustc_peek(potentially_uninitialized)` would actually
615 /// double-check that dataflow did indeed compute that it is
616 /// uninitialized at that point in the control flow.
617 pub fn rustc_peek<T>(_: T) -> T;
619 /// Aborts the execution of the process.
621 /// The stabilized version of this intrinsic is
622 /// [`std::process::abort`](../../std/process/fn.abort.html)
625 /// Tells LLVM that this point in the code is not reachable, enabling
626 /// further optimizations.
628 /// N.B., this is very different from the `unreachable!()` macro: Unlike the
629 /// macro, which panics when it is executed, it is *undefined behavior* to
630 /// reach code marked with this function.
632 /// The stabilized version of this intrinsic is
633 /// [`std::hint::unreachable_unchecked`](../../std/hint/fn.unreachable_unchecked.html).
634 pub fn unreachable() -> !;
636 /// Informs the optimizer that a condition is always true.
637 /// If the condition is false, the behavior is undefined.
639 /// No code is generated for this intrinsic, but the optimizer will try
640 /// to preserve it (and its condition) between passes, which may interfere
641 /// with optimization of surrounding code and reduce performance. It should
642 /// not be used if the invariant can be discovered by the optimizer on its
643 /// own, or if it does not enable any significant optimizations.
644 pub fn assume(b: bool);
646 /// Hints to the compiler that branch condition is likely to be true.
647 /// Returns the value passed to it.
649 /// Any use other than with `if` statements will probably not have an effect.
650 pub fn likely(b: bool) -> bool;
652 /// Hints to the compiler that branch condition is likely to be false.
653 /// Returns the value passed to it.
655 /// Any use other than with `if` statements will probably not have an effect.
656 pub fn unlikely(b: bool) -> bool;
658 /// Executes a breakpoint trap, for inspection by a debugger.
661 /// The size of a type in bytes.
663 /// More specifically, this is the offset in bytes between successive
664 /// items of the same type, including alignment padding.
666 /// The stabilized version of this intrinsic is
667 /// [`std::mem::size_of`](../../std/mem/fn.size_of.html).
668 pub fn size_of<T>() -> usize;
670 /// Moves a value to an uninitialized memory location.
672 /// Drop glue is not run on the destination.
673 pub fn move_val_init<T>(dst: *mut T, src: T);
675 pub fn min_align_of<T>() -> usize;
676 pub fn pref_align_of<T>() -> usize;
678 /// The size of the referenced value in bytes.
680 /// The stabilized version of this intrinsic is
681 /// [`std::mem::size_of_val`](../../std/mem/fn.size_of_val.html).
682 pub fn size_of_val<T: ?Sized>(_: &T) -> usize;
683 pub fn min_align_of_val<T: ?Sized>(_: &T) -> usize;
685 /// Gets a static string slice containing the name of a type.
686 pub fn type_name<T: ?Sized>() -> &'static str;
688 /// Gets an identifier which is globally unique to the specified type. This
689 /// function will return the same value for a type regardless of whichever
690 /// crate it is invoked in.
691 pub fn type_id<T: ?Sized + 'static>() -> u64;
693 /// A guard for unsafe functions that cannot ever be executed if `T` is uninhabited:
694 /// This will statically either panic, or do nothing.
695 pub fn panic_if_uninhabited<T>();
697 /// Creates a value initialized to zero.
699 /// `init` is unsafe because it returns a zeroed-out datum,
700 /// which is unsafe unless `T` is `Copy`. Also, even if T is
701 /// `Copy`, an all-zero value may not correspond to any legitimate
702 /// state for the type in question.
703 pub fn init<T>() -> T;
705 /// Creates an uninitialized value.
707 /// `uninit` is unsafe because there is no guarantee of what its
708 /// contents are. In particular its drop-flag may be set to any
709 /// state, which means it may claim either dropped or
710 /// undropped. In the general case one must use `ptr::write` to
711 /// initialize memory previous set to the result of `uninit`.
712 pub fn uninit<T>() -> T;
714 /// Moves a value out of scope without running drop glue.
715 pub fn forget<T: ?Sized>(_: T);
717 /// Reinterprets the bits of a value of one type as another type.
719 /// Both types must have the same size. Neither the original, nor the result,
720 /// may be an [invalid value](../../nomicon/what-unsafe-does.html).
722 /// `transmute` is semantically equivalent to a bitwise move of one type
723 /// into another. It copies the bits from the source value into the
724 /// destination value, then forgets the original. It's equivalent to C's
725 /// `memcpy` under the hood, just like `transmute_copy`.
727 /// `transmute` is **incredibly** unsafe. There are a vast number of ways to
728 /// cause [undefined behavior][ub] with this function. `transmute` should be
729 /// the absolute last resort.
731 /// The [nomicon](../../nomicon/transmutes.html) has additional
734 /// [ub]: ../../reference/behavior-considered-undefined.html
738 /// There are a few things that `transmute` is really useful for.
740 /// Getting the bitpattern of a floating point type (or, more generally,
741 /// type punning, when `T` and `U` aren't pointers):
744 /// let bitpattern = unsafe {
745 /// std::mem::transmute::<f32, u32>(1.0)
747 /// assert_eq!(bitpattern, 0x3F800000);
750 /// Turning a pointer into a function pointer. This is *not* portable to
751 /// machines where function pointers and data pointers have different sizes.
754 /// fn foo() -> i32 {
757 /// let pointer = foo as *const ();
758 /// let function = unsafe {
759 /// std::mem::transmute::<*const (), fn() -> i32>(pointer)
761 /// assert_eq!(function(), 0);
764 /// Extending a lifetime, or shortening an invariant lifetime. This is
765 /// advanced, very unsafe Rust!
768 /// struct R<'a>(&'a i32);
769 /// unsafe fn extend_lifetime<'b>(r: R<'b>) -> R<'static> {
770 /// std::mem::transmute::<R<'b>, R<'static>>(r)
773 /// unsafe fn shorten_invariant_lifetime<'b, 'c>(r: &'b mut R<'static>)
774 /// -> &'b mut R<'c> {
775 /// std::mem::transmute::<&'b mut R<'static>, &'b mut R<'c>>(r)
781 /// Don't despair: many uses of `transmute` can be achieved through other means.
782 /// Below are common applications of `transmute` which can be replaced with safer
785 /// Turning a pointer into a `usize`:
789 /// let ptr_num_transmute = unsafe {
790 /// std::mem::transmute::<&i32, usize>(ptr)
793 /// // Use an `as` cast instead
794 /// let ptr_num_cast = ptr as *const i32 as usize;
797 /// Turning a `*mut T` into an `&mut T`:
800 /// let ptr: *mut i32 = &mut 0;
801 /// let ref_transmuted = unsafe {
802 /// std::mem::transmute::<*mut i32, &mut i32>(ptr)
805 /// // Use a reborrow instead
806 /// let ref_casted = unsafe { &mut *ptr };
809 /// Turning an `&mut T` into an `&mut U`:
812 /// let ptr = &mut 0;
813 /// let val_transmuted = unsafe {
814 /// std::mem::transmute::<&mut i32, &mut u32>(ptr)
817 /// // Now, put together `as` and reborrowing - note the chaining of `as`
818 /// // `as` is not transitive
819 /// let val_casts = unsafe { &mut *(ptr as *mut i32 as *mut u32) };
822 /// Turning an `&str` into an `&[u8]`:
825 /// // this is not a good way to do this.
826 /// let slice = unsafe { std::mem::transmute::<&str, &[u8]>("Rust") };
827 /// assert_eq!(slice, &[82, 117, 115, 116]);
829 /// // You could use `str::as_bytes`
830 /// let slice = "Rust".as_bytes();
831 /// assert_eq!(slice, &[82, 117, 115, 116]);
833 /// // Or, just use a byte string, if you have control over the string
835 /// assert_eq!(b"Rust", &[82, 117, 115, 116]);
838 /// Turning a `Vec<&T>` into a `Vec<Option<&T>>`:
841 /// let store = [0, 1, 2, 3];
842 /// let mut v_orig = store.iter().collect::<Vec<&i32>>();
844 /// // Using transmute: this is Undefined Behavior, and a bad idea.
845 /// // However, it is no-copy.
846 /// let v_transmuted = unsafe {
847 /// std::mem::transmute::<Vec<&i32>, Vec<Option<&i32>>>(
851 /// // This is the suggested, safe way.
852 /// // It does copy the entire vector, though, into a new array.
853 /// let v_collected = v_orig.clone()
855 /// .map(|r| Some(r))
856 /// .collect::<Vec<Option<&i32>>>();
858 /// // The no-copy, unsafe way, still using transmute, but not UB.
859 /// // This is equivalent to the original, but safer, and reuses the
860 /// // same `Vec` internals. Therefore, the new inner type must have the
861 /// // exact same size, and the same alignment, as the old type.
862 /// // The same caveats exist for this method as transmute, for
863 /// // the original inner type (`&i32`) to the converted inner type
864 /// // (`Option<&i32>`), so read the nomicon pages linked above.
865 /// let v_from_raw = unsafe {
866 /// Vec::from_raw_parts(v_orig.as_mut_ptr() as *mut Option<&i32>,
868 /// v_orig.capacity())
870 /// std::mem::forget(v_orig);
873 /// Implementing `split_at_mut`:
876 /// use std::{slice, mem};
878 /// // There are multiple ways to do this, and there are multiple problems
879 /// // with the following (transmute) way.
880 /// fn split_at_mut_transmute<T>(slice: &mut [T], mid: usize)
881 /// -> (&mut [T], &mut [T]) {
882 /// let len = slice.len();
883 /// assert!(mid <= len);
885 /// let slice2 = mem::transmute::<&mut [T], &mut [T]>(slice);
886 /// // first: transmute is not typesafe; all it checks is that T and
887 /// // U are of the same size. Second, right here, you have two
888 /// // mutable references pointing to the same memory.
889 /// (&mut slice[0..mid], &mut slice2[mid..len])
893 /// // This gets rid of the typesafety problems; `&mut *` will *only* give
894 /// // you an `&mut T` from an `&mut T` or `*mut T`.
895 /// fn split_at_mut_casts<T>(slice: &mut [T], mid: usize)
896 /// -> (&mut [T], &mut [T]) {
897 /// let len = slice.len();
898 /// assert!(mid <= len);
900 /// let slice2 = &mut *(slice as *mut [T]);
901 /// // however, you still have two mutable references pointing to
902 /// // the same memory.
903 /// (&mut slice[0..mid], &mut slice2[mid..len])
907 /// // This is how the standard library does it. This is the best method, if
908 /// // you need to do something like this
909 /// fn split_at_stdlib<T>(slice: &mut [T], mid: usize)
910 /// -> (&mut [T], &mut [T]) {
911 /// let len = slice.len();
912 /// assert!(mid <= len);
914 /// let ptr = slice.as_mut_ptr();
915 /// // This now has three mutable references pointing at the same
916 /// // memory. `slice`, the rvalue ret.0, and the rvalue ret.1.
917 /// // `slice` is never used after `let ptr = ...`, and so one can
918 /// // treat it as "dead", and therefore, you only have two real
919 /// // mutable slices.
920 /// (slice::from_raw_parts_mut(ptr, mid),
921 /// slice::from_raw_parts_mut(ptr.add(mid), len - mid))
925 #[stable(feature = "rust1", since = "1.0.0")]
926 pub fn transmute<T, U>(e: T) -> U;
928 /// Returns `true` if the actual type given as `T` requires drop
929 /// glue; returns `false` if the actual type provided for `T`
930 /// implements `Copy`.
932 /// If the actual type neither requires drop glue nor implements
933 /// `Copy`, then may return `true` or `false`.
935 /// The stabilized version of this intrinsic is
936 /// [`std::mem::needs_drop`](../../std/mem/fn.needs_drop.html).
937 pub fn needs_drop<T>() -> bool;
939 /// Calculates the offset from a pointer.
941 /// This is implemented as an intrinsic to avoid converting to and from an
942 /// integer, since the conversion would throw away aliasing information.
946 /// Both the starting and resulting pointer must be either in bounds or one
947 /// byte past the end of an allocated object. If either pointer is out of
948 /// bounds or arithmetic overflow occurs then any further use of the
949 /// returned value will result in undefined behavior.
950 pub fn offset<T>(dst: *const T, offset: isize) -> *const T;
952 /// Calculates the offset from a pointer, potentially wrapping.
954 /// This is implemented as an intrinsic to avoid converting to and from an
955 /// integer, since the conversion inhibits certain optimizations.
959 /// Unlike the `offset` intrinsic, this intrinsic does not restrict the
960 /// resulting pointer to point into or one byte past the end of an allocated
961 /// object, and it wraps with two's complement arithmetic. The resulting
962 /// value is not necessarily valid to be used to actually access memory.
963 pub fn arith_offset<T>(dst: *const T, offset: isize) -> *const T;
965 /// Equivalent to the appropriate `llvm.memcpy.p0i8.0i8.*` intrinsic, with
966 /// a size of `count` * `size_of::<T>()` and an alignment of
967 /// `min_align_of::<T>()`
969 /// The volatile parameter is set to `true`, so it will not be optimized out
970 /// unless size is equal to zero.
971 pub fn volatile_copy_nonoverlapping_memory<T>(dst: *mut T, src: *const T,
973 /// Equivalent to the appropriate `llvm.memmove.p0i8.0i8.*` intrinsic, with
974 /// a size of `count` * `size_of::<T>()` and an alignment of
975 /// `min_align_of::<T>()`
977 /// The volatile parameter is set to `true`, so it will not be optimized out
978 /// unless size is equal to zero.
979 pub fn volatile_copy_memory<T>(dst: *mut T, src: *const T, count: usize);
980 /// Equivalent to the appropriate `llvm.memset.p0i8.*` intrinsic, with a
981 /// size of `count` * `size_of::<T>()` and an alignment of
982 /// `min_align_of::<T>()`.
984 /// The volatile parameter is set to `true`, so it will not be optimized out
985 /// unless size is equal to zero.
986 pub fn volatile_set_memory<T>(dst: *mut T, val: u8, count: usize);
988 /// Performs a volatile load from the `src` pointer.
989 /// The stabilized version of this intrinsic is
990 /// [`std::ptr::read_volatile`](../../std/ptr/fn.read_volatile.html).
991 pub fn volatile_load<T>(src: *const T) -> T;
992 /// Performs a volatile store to the `dst` pointer.
993 /// The stabilized version of this intrinsic is
994 /// [`std::ptr::write_volatile`](../../std/ptr/fn.write_volatile.html).
995 pub fn volatile_store<T>(dst: *mut T, val: T);
997 /// Performs a volatile load from the `src` pointer
998 /// The pointer is not required to be aligned.
999 pub fn unaligned_volatile_load<T>(src: *const T) -> T;
1000 /// Performs a volatile store to the `dst` pointer.
1001 /// The pointer is not required to be aligned.
1002 pub fn unaligned_volatile_store<T>(dst: *mut T, val: T);
1004 /// Returns the square root of an `f32`
1005 pub fn sqrtf32(x: f32) -> f32;
1006 /// Returns the square root of an `f64`
1007 pub fn sqrtf64(x: f64) -> f64;
1009 /// Raises an `f32` to an integer power.
1010 pub fn powif32(a: f32, x: i32) -> f32;
1011 /// Raises an `f64` to an integer power.
1012 pub fn powif64(a: f64, x: i32) -> f64;
1014 /// Returns the sine of an `f32`.
1015 pub fn sinf32(x: f32) -> f32;
1016 /// Returns the sine of an `f64`.
1017 pub fn sinf64(x: f64) -> f64;
1019 /// Returns the cosine of an `f32`.
1020 pub fn cosf32(x: f32) -> f32;
1021 /// Returns the cosine of an `f64`.
1022 pub fn cosf64(x: f64) -> f64;
1024 /// Raises an `f32` to an `f32` power.
1025 pub fn powf32(a: f32, x: f32) -> f32;
1026 /// Raises an `f64` to an `f64` power.
1027 pub fn powf64(a: f64, x: f64) -> f64;
1029 /// Returns the exponential of an `f32`.
1030 pub fn expf32(x: f32) -> f32;
1031 /// Returns the exponential of an `f64`.
1032 pub fn expf64(x: f64) -> f64;
1034 /// Returns 2 raised to the power of an `f32`.
1035 pub fn exp2f32(x: f32) -> f32;
1036 /// Returns 2 raised to the power of an `f64`.
1037 pub fn exp2f64(x: f64) -> f64;
1039 /// Returns the natural logarithm of an `f32`.
1040 pub fn logf32(x: f32) -> f32;
1041 /// Returns the natural logarithm of an `f64`.
1042 pub fn logf64(x: f64) -> f64;
1044 /// Returns the base 10 logarithm of an `f32`.
1045 pub fn log10f32(x: f32) -> f32;
1046 /// Returns the base 10 logarithm of an `f64`.
1047 pub fn log10f64(x: f64) -> f64;
1049 /// Returns the base 2 logarithm of an `f32`.
1050 pub fn log2f32(x: f32) -> f32;
1051 /// Returns the base 2 logarithm of an `f64`.
1052 pub fn log2f64(x: f64) -> f64;
1054 /// Returns `a * b + c` for `f32` values.
1055 pub fn fmaf32(a: f32, b: f32, c: f32) -> f32;
1056 /// Returns `a * b + c` for `f64` values.
1057 pub fn fmaf64(a: f64, b: f64, c: f64) -> f64;
1059 /// Returns the absolute value of an `f32`.
1060 pub fn fabsf32(x: f32) -> f32;
1061 /// Returns the absolute value of an `f64`.
1062 pub fn fabsf64(x: f64) -> f64;
1064 /// Copies the sign from `y` to `x` for `f32` values.
1065 pub fn copysignf32(x: f32, y: f32) -> f32;
1066 /// Copies the sign from `y` to `x` for `f64` values.
1067 pub fn copysignf64(x: f64, y: f64) -> f64;
1069 /// Returns the largest integer less than or equal to an `f32`.
1070 pub fn floorf32(x: f32) -> f32;
1071 /// Returns the largest integer less than or equal to an `f64`.
1072 pub fn floorf64(x: f64) -> f64;
1074 /// Returns the smallest integer greater than or equal to an `f32`.
1075 pub fn ceilf32(x: f32) -> f32;
1076 /// Returns the smallest integer greater than or equal to an `f64`.
1077 pub fn ceilf64(x: f64) -> f64;
1079 /// Returns the integer part of an `f32`.
1080 pub fn truncf32(x: f32) -> f32;
1081 /// Returns the integer part of an `f64`.
1082 pub fn truncf64(x: f64) -> f64;
1084 /// Returns the nearest integer to an `f32`. May raise an inexact floating-point exception
1085 /// if the argument is not an integer.
1086 pub fn rintf32(x: f32) -> f32;
1087 /// Returns the nearest integer to an `f64`. May raise an inexact floating-point exception
1088 /// if the argument is not an integer.
1089 pub fn rintf64(x: f64) -> f64;
1091 /// Returns the nearest integer to an `f32`.
1092 pub fn nearbyintf32(x: f32) -> f32;
1093 /// Returns the nearest integer to an `f64`.
1094 pub fn nearbyintf64(x: f64) -> f64;
1096 /// Returns the nearest integer to an `f32`. Rounds half-way cases away from zero.
1097 pub fn roundf32(x: f32) -> f32;
1098 /// Returns the nearest integer to an `f64`. Rounds half-way cases away from zero.
1099 pub fn roundf64(x: f64) -> f64;
1101 /// Float addition that allows optimizations based on algebraic rules.
1102 /// May assume inputs are finite.
1103 pub fn fadd_fast<T>(a: T, b: T) -> T;
1105 /// Float subtraction that allows optimizations based on algebraic rules.
1106 /// May assume inputs are finite.
1107 pub fn fsub_fast<T>(a: T, b: T) -> T;
1109 /// Float multiplication that allows optimizations based on algebraic rules.
1110 /// May assume inputs are finite.
1111 pub fn fmul_fast<T>(a: T, b: T) -> T;
1113 /// Float division that allows optimizations based on algebraic rules.
1114 /// May assume inputs are finite.
1115 pub fn fdiv_fast<T>(a: T, b: T) -> T;
1117 /// Float remainder that allows optimizations based on algebraic rules.
1118 /// May assume inputs are finite.
1119 pub fn frem_fast<T>(a: T, b: T) -> T;
1122 /// Returns the number of bits set in an integer type `T`
1123 pub fn ctpop<T>(x: T) -> T;
1125 /// Returns the number of leading unset bits (zeroes) in an integer type `T`.
1130 /// #![feature(core_intrinsics)]
1132 /// use std::intrinsics::ctlz;
1134 /// let x = 0b0001_1100_u8;
1135 /// let num_leading = ctlz(x);
1136 /// assert_eq!(num_leading, 3);
1139 /// An `x` with value `0` will return the bit width of `T`.
1142 /// #![feature(core_intrinsics)]
1144 /// use std::intrinsics::ctlz;
1147 /// let num_leading = ctlz(x);
1148 /// assert_eq!(num_leading, 16);
1150 pub fn ctlz<T>(x: T) -> T;
1152 /// Like `ctlz`, but extra-unsafe as it returns `undef` when
1153 /// given an `x` with value `0`.
1158 /// #![feature(core_intrinsics)]
1160 /// use std::intrinsics::ctlz_nonzero;
1162 /// let x = 0b0001_1100_u8;
1163 /// let num_leading = unsafe { ctlz_nonzero(x) };
1164 /// assert_eq!(num_leading, 3);
1166 pub fn ctlz_nonzero<T>(x: T) -> T;
1168 /// Returns the number of trailing unset bits (zeroes) in an integer type `T`.
1173 /// #![feature(core_intrinsics)]
1175 /// use std::intrinsics::cttz;
1177 /// let x = 0b0011_1000_u8;
1178 /// let num_trailing = cttz(x);
1179 /// assert_eq!(num_trailing, 3);
1182 /// An `x` with value `0` will return the bit width of `T`:
1185 /// #![feature(core_intrinsics)]
1187 /// use std::intrinsics::cttz;
1190 /// let num_trailing = cttz(x);
1191 /// assert_eq!(num_trailing, 16);
1193 pub fn cttz<T>(x: T) -> T;
1195 /// Like `cttz`, but extra-unsafe as it returns `undef` when
1196 /// given an `x` with value `0`.
1201 /// #![feature(core_intrinsics)]
1203 /// use std::intrinsics::cttz_nonzero;
1205 /// let x = 0b0011_1000_u8;
1206 /// let num_trailing = unsafe { cttz_nonzero(x) };
1207 /// assert_eq!(num_trailing, 3);
1209 pub fn cttz_nonzero<T>(x: T) -> T;
1211 /// Reverses the bytes in an integer type `T`.
1212 pub fn bswap<T>(x: T) -> T;
1214 /// Reverses the bits in an integer type `T`.
1215 pub fn bitreverse<T>(x: T) -> T;
1217 /// Performs checked integer addition.
1218 /// The stabilized versions of this intrinsic are available on the integer
1219 /// primitives via the `overflowing_add` method. For example,
1220 /// [`std::u32::overflowing_add`](../../std/primitive.u32.html#method.overflowing_add)
1221 pub fn add_with_overflow<T>(x: T, y: T) -> (T, bool);
1223 /// Performs checked integer subtraction
1224 /// The stabilized versions of this intrinsic are available on the integer
1225 /// primitives via the `overflowing_sub` method. For example,
1226 /// [`std::u32::overflowing_sub`](../../std/primitive.u32.html#method.overflowing_sub)
1227 pub fn sub_with_overflow<T>(x: T, y: T) -> (T, bool);
1229 /// Performs checked integer multiplication
1230 /// The stabilized versions of this intrinsic are available on the integer
1231 /// primitives via the `overflowing_mul` method. For example,
1232 /// [`std::u32::overflowing_mul`](../../std/primitive.u32.html#method.overflowing_mul)
1233 pub fn mul_with_overflow<T>(x: T, y: T) -> (T, bool);
1235 /// Performs an exact division, resulting in undefined behavior where
1236 /// `x % y != 0` or `y == 0` or `x == T::min_value() && y == -1`
1237 pub fn exact_div<T>(x: T, y: T) -> T;
1239 /// Performs an unchecked division, resulting in undefined behavior
1240 /// where y = 0 or x = `T::min_value()` and y = -1
1241 pub fn unchecked_div<T>(x: T, y: T) -> T;
1242 /// Returns the remainder of an unchecked division, resulting in
1243 /// undefined behavior where y = 0 or x = `T::min_value()` and y = -1
1244 pub fn unchecked_rem<T>(x: T, y: T) -> T;
1246 /// Performs an unchecked left shift, resulting in undefined behavior when
1247 /// y < 0 or y >= N, where N is the width of T in bits.
1248 pub fn unchecked_shl<T>(x: T, y: T) -> T;
1249 /// Performs an unchecked right shift, resulting in undefined behavior when
1250 /// y < 0 or y >= N, where N is the width of T in bits.
1251 pub fn unchecked_shr<T>(x: T, y: T) -> T;
1253 /// Performs rotate left.
1254 /// The stabilized versions of this intrinsic are available on the integer
1255 /// primitives via the `rotate_left` method. For example,
1256 /// [`std::u32::rotate_left`](../../std/primitive.u32.html#method.rotate_left)
1257 pub fn rotate_left<T>(x: T, y: T) -> T;
1259 /// Performs rotate right.
1260 /// The stabilized versions of this intrinsic are available on the integer
1261 /// primitives via the `rotate_right` method. For example,
1262 /// [`std::u32::rotate_right`](../../std/primitive.u32.html#method.rotate_right)
1263 pub fn rotate_right<T>(x: T, y: T) -> T;
1265 /// Returns (a + b) mod 2<sup>N</sup>, where N is the width of T in bits.
1266 /// The stabilized versions of this intrinsic are available on the integer
1267 /// primitives via the `wrapping_add` method. For example,
1268 /// [`std::u32::wrapping_add`](../../std/primitive.u32.html#method.wrapping_add)
1269 pub fn overflowing_add<T>(a: T, b: T) -> T;
1270 /// Returns (a - b) mod 2<sup>N</sup>, where N is the width of T in bits.
1271 /// The stabilized versions of this intrinsic are available on the integer
1272 /// primitives via the `wrapping_sub` method. For example,
1273 /// [`std::u32::wrapping_sub`](../../std/primitive.u32.html#method.wrapping_sub)
1274 pub fn overflowing_sub<T>(a: T, b: T) -> T;
1275 /// Returns (a * b) mod 2<sup>N</sup>, where N is the width of T in bits.
1276 /// The stabilized versions of this intrinsic are available on the integer
1277 /// primitives via the `wrapping_mul` method. For example,
1278 /// [`std::u32::wrapping_mul`](../../std/primitive.u32.html#method.wrapping_mul)
1279 pub fn overflowing_mul<T>(a: T, b: T) -> T;
1281 /// Computes `a + b`, while saturating at numeric bounds.
1282 /// The stabilized versions of this intrinsic are available on the integer
1283 /// primitives via the `saturating_add` method. For example,
1284 /// [`std::u32::saturating_add`](../../std/primitive.u32.html#method.saturating_add)
1286 pub fn saturating_add<T>(a: T, b: T) -> T;
1287 /// Computes `a - b`, while saturating at numeric bounds.
1288 /// The stabilized versions of this intrinsic are available on the integer
1289 /// primitives via the `saturating_sub` method. For example,
1290 /// [`std::u32::saturating_sub`](../../std/primitive.u32.html#method.saturating_sub)
1292 pub fn saturating_sub<T>(a: T, b: T) -> T;
1294 /// Returns the value of the discriminant for the variant in 'v',
1295 /// cast to a `u64`; if `T` has no discriminant, returns 0.
1296 pub fn discriminant_value<T>(v: &T) -> u64;
1298 /// Rust's "try catch" construct which invokes the function pointer `f` with
1299 /// the data pointer `data`.
1301 /// The third pointer is a target-specific data pointer which is filled in
1302 /// with the specifics of the exception that occurred. For examples on Unix
1303 /// platforms this is a `*mut *mut T` which is filled in by the compiler and
1304 /// on MSVC it's `*mut [usize; 2]`. For more information see the compiler's
1305 /// source as well as std's catch implementation.
1306 pub fn try(f: fn(*mut u8), data: *mut u8, local_ptr: *mut u8) -> i32;
1308 /// Emits a `!nontemporal` store according to LLVM (see their docs).
1309 /// Probably will never become stable.
1310 pub fn nontemporal_store<T>(ptr: *mut T, val: T);
1313 mod real_intrinsics {
1314 extern "rust-intrinsic" {
1315 /// Copies `count * size_of::<T>()` bytes from `src` to `dst`. The source
1316 /// and destination must *not* overlap.
1317 /// For the full docs, see the stabilized wrapper [`copy_nonoverlapping`].
1319 /// [`copy_nonoverlapping`]: ../../std/ptr/fn.copy_nonoverlapping.html
1320 pub fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
1322 /// Copies `count * size_of::<T>()` bytes from `src` to `dst`. The source
1323 /// and destination may overlap.
1324 /// For the full docs, see the stabilized wrapper [`copy`].
1326 /// [`copy`]: ../../std/ptr/fn.copy.html
1327 pub fn copy<T>(src: *const T, dst: *mut T, count: usize);
1329 /// Sets `count * size_of::<T>()` bytes of memory starting at `dst` to
1331 /// For the full docs, see the stabilized wrapper [`write_bytes`].
1333 /// [`write_bytes`]: ../../std/ptr/fn.write_bytes.html
1334 pub fn write_bytes<T>(dst: *mut T, val: u8, count: usize);
1338 /// Copies `count * size_of::<T>()` bytes from `src` to `dst`. The source
1339 /// and destination must *not* overlap.
1341 /// For regions of memory which might overlap, use [`copy`] instead.
1343 /// `copy_nonoverlapping` is semantically equivalent to C's [`memcpy`], but
1344 /// with the argument order swapped.
1346 /// [`copy`]: ./fn.copy.html
1347 /// [`memcpy`]: https://en.cppreference.com/w/c/string/byte/memcpy
1351 /// Behavior is undefined if any of the following conditions are violated:
1353 /// * `src` must be [valid] for reads of `count * size_of::<T>()` bytes.
1355 /// * `dst` must be [valid] for writes of `count * size_of::<T>()` bytes.
1357 /// * Both `src` and `dst` must be properly aligned.
1359 /// * The region of memory beginning at `src` with a size of `count *
1360 /// size_of::<T>()` bytes must *not* overlap with the region of memory
1361 /// beginning at `dst` with the same size.
1363 /// Like [`read`], `copy_nonoverlapping` creates a bitwise copy of `T`, regardless of
1364 /// whether `T` is [`Copy`]. If `T` is not [`Copy`], using *both* the values
1365 /// in the region beginning at `*src` and the region beginning at `*dst` can
1366 /// [violate memory safety][read-ownership].
1368 /// Note that even if the effectively copied size (`count * size_of::<T>()`) is
1369 /// `0`, the pointers must be non-NULL and properly aligned.
1371 /// [`Copy`]: ../marker/trait.Copy.html
1372 /// [`read`]: ../ptr/fn.read.html
1373 /// [read-ownership]: ../ptr/fn.read.html#ownership-of-the-returned-value
1374 /// [valid]: ../ptr/index.html#safety
1378 /// Manually implement [`Vec::append`]:
1383 /// /// Moves all the elements of `src` into `dst`, leaving `src` empty.
1384 /// fn append<T>(dst: &mut Vec<T>, src: &mut Vec<T>) {
1385 /// let src_len = src.len();
1386 /// let dst_len = dst.len();
1388 /// // Ensure that `dst` has enough capacity to hold all of `src`.
1389 /// dst.reserve(src_len);
1392 /// // The call to offset is always safe because `Vec` will never
1393 /// // allocate more than `isize::MAX` bytes.
1394 /// let dst_ptr = dst.as_mut_ptr().offset(dst_len as isize);
1395 /// let src_ptr = src.as_ptr();
1397 /// // Truncate `src` without dropping its contents. We do this first,
1398 /// // to avoid problems in case something further down panics.
1401 /// // The two regions cannot overlap because mutable references do
1402 /// // not alias, and two different vectors cannot own the same
1404 /// ptr::copy_nonoverlapping(src_ptr, dst_ptr, src_len);
1406 /// // Notify `dst` that it now holds the contents of `src`.
1407 /// dst.set_len(dst_len + src_len);
1411 /// let mut a = vec!['r'];
1412 /// let mut b = vec!['u', 's', 't'];
1414 /// append(&mut a, &mut b);
1416 /// assert_eq!(a, &['r', 'u', 's', 't']);
1417 /// assert!(b.is_empty());
1420 /// [`Vec::append`]: ../../std/vec/struct.Vec.html#method.append
1421 #[stable(feature = "rust1", since = "1.0.0")]
1423 pub unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize) {
1424 real_intrinsics::copy_nonoverlapping(src, dst, count);
1427 /// Copies `count * size_of::<T>()` bytes from `src` to `dst`. The source
1428 /// and destination may overlap.
1430 /// If the source and destination will *never* overlap,
1431 /// [`copy_nonoverlapping`] can be used instead.
1433 /// `copy` is semantically equivalent to C's [`memmove`], but with the argument
1434 /// order swapped. Copying takes place as if the bytes were copied from `src`
1435 /// to a temporary array and then copied from the array to `dst`.
1437 /// [`copy_nonoverlapping`]: ./fn.copy_nonoverlapping.html
1438 /// [`memmove`]: https://en.cppreference.com/w/c/string/byte/memmove
1442 /// Behavior is undefined if any of the following conditions are violated:
1444 /// * `src` must be [valid] for reads of `count * size_of::<T>()` bytes.
1446 /// * `dst` must be [valid] for writes of `count * size_of::<T>()` bytes.
1448 /// * Both `src` and `dst` must be properly aligned.
1450 /// Like [`read`], `copy` creates a bitwise copy of `T`, regardless of
1451 /// whether `T` is [`Copy`]. If `T` is not [`Copy`], using both the values
1452 /// in the region beginning at `*src` and the region beginning at `*dst` can
1453 /// [violate memory safety][read-ownership].
1455 /// Note that even if the effectively copied size (`count * size_of::<T>()`) is
1456 /// `0`, the pointers must be non-NULL and properly aligned.
1458 /// [`Copy`]: ../marker/trait.Copy.html
1459 /// [`read`]: ../ptr/fn.read.html
1460 /// [read-ownership]: ../ptr/fn.read.html#ownership-of-the-returned-value
1461 /// [valid]: ../ptr/index.html#safety
1465 /// Efficiently create a Rust vector from an unsafe buffer:
1470 /// # #[allow(dead_code)]
1471 /// unsafe fn from_buf_raw<T>(ptr: *const T, elts: usize) -> Vec<T> {
1472 /// let mut dst = Vec::with_capacity(elts);
1473 /// dst.set_len(elts);
1474 /// ptr::copy(ptr, dst.as_mut_ptr(), elts);
1478 #[stable(feature = "rust1", since = "1.0.0")]
1480 pub unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
1481 real_intrinsics::copy(src, dst, count)
1484 /// Sets `count * size_of::<T>()` bytes of memory starting at `dst` to
1487 /// `write_bytes` is similar to C's [`memset`], but sets `count *
1488 /// size_of::<T>()` bytes to `val`.
1490 /// [`memset`]: https://en.cppreference.com/w/c/string/byte/memset
1494 /// Behavior is undefined if any of the following conditions are violated:
1496 /// * `dst` must be [valid] for writes of `count * size_of::<T>()` bytes.
1498 /// * `dst` must be properly aligned.
1500 /// Additionally, the caller must ensure that writing `count *
1501 /// size_of::<T>()` bytes to the given region of memory results in a valid
1502 /// value of `T`. Using a region of memory typed as a `T` that contains an
1503 /// invalid value of `T` is undefined behavior.
1505 /// Note that even if the effectively copied size (`count * size_of::<T>()`) is
1506 /// `0`, the pointer must be non-NULL and properly aligned.
1508 /// [valid]: ../ptr/index.html#safety
1517 /// let mut vec = vec![0u32; 4];
1519 /// let vec_ptr = vec.as_mut_ptr();
1520 /// ptr::write_bytes(vec_ptr, 0xfe, 2);
1522 /// assert_eq!(vec, [0xfefefefe, 0xfefefefe, 0, 0]);
1525 /// Creating an invalid value:
1530 /// let mut v = Box::new(0i32);
1533 /// // Leaks the previously held value by overwriting the `Box<T>` with
1534 /// // a null pointer.
1535 /// ptr::write_bytes(&mut v as *mut Box<i32>, 0, 1);
1538 /// // At this point, using or dropping `v` results in undefined behavior.
1539 /// // drop(v); // ERROR
1541 /// // Even leaking `v` "uses" it, and hence is undefined behavior.
1542 /// // mem::forget(v); // ERROR
1544 /// // In fact, `v` is invalid according to basic type layout invariants, so *any*
1545 /// // operation touching it is undefined behavior.
1546 /// // let v2 = v; // ERROR
1549 /// // Let us instead put in a valid value
1550 /// ptr::write(&mut v as *mut Box<i32>, Box::new(42i32));
1553 /// // Now the box is fine
1554 /// assert_eq!(*v, 42);
1556 #[stable(feature = "rust1", since = "1.0.0")]
1558 pub unsafe fn write_bytes<T>(dst: *mut T, val: u8, count: usize) {
1559 real_intrinsics::write_bytes(dst, val, count)