src/libcore/intrinsics.rs

   1 // Copyright 2013 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! rustc compiler intrinsics.
  12 //!
  13 //! The corresponding definitions are in librustc_trans/intrinsic.rs.
  14 //!
  15 //! # Volatiles
  16 //!
  17 //! The volatile intrinsics provide operations intended to act on I/O
  18 //! memory, which are guaranteed to not be reordered by the compiler
  19 //! across other volatile intrinsics. See the LLVM documentation on
  20 //! [[volatile]].
  21 //!
  22 //! [volatile]: http://llvm.org/docs/LangRef.html#volatile-memory-accesses
  23 //!
  24 //! # Atomics
  25 //!
  26 //! The atomic intrinsics provide common atomic operations on machine
  27 //! words, with multiple possible memory orderings. They obey the same
  28 //! semantics as C++11. See the LLVM documentation on [[atomics]].
  29 //!
  30 //! [atomics]: http://llvm.org/docs/Atomics.html
  31 //!
  32 //! A quick refresher on memory ordering:
  33 //!
  34 //! * Acquire - a barrier for acquiring a lock. Subsequent reads and writes
  35 //!   take place after the barrier.
  36 //! * Release - a barrier for releasing a lock. Preceding reads and writes
  37 //!   take place before the barrier.
  38 //! * Sequentially consistent - sequentially consistent operations are
  39 //!   guaranteed to happen in order. This is the standard mode for working
  40 //!   with atomic types and is equivalent to Java's `volatile`.
  41
  42 #![unstable(feature = "core_intrinsics",
  43             reason = "intrinsics are unlikely to ever be stabilized, instead \
  44                       they should be used through stabilized interfaces \
  45                       in the rest of the standard library",
  46             issue = "0")]
  47 #![allow(missing_docs)]
  48
  49 extern "rust-intrinsic" {
  50
  51     // NB: These intrinsics take raw pointers because they mutate aliased
  52     // memory, which is not valid for either `&` or `&mut`.
  53
  54     pub fn atomic_cxchg<T>(dst: *mut T, old: T, src: T) -> (T, bool);
  55     pub fn atomic_cxchg_acq<T>(dst: *mut T, old: T, src: T) -> (T, bool);
  56     pub fn atomic_cxchg_rel<T>(dst: *mut T, old: T, src: T) -> (T, bool);
  57     pub fn atomic_cxchg_acqrel<T>(dst: *mut T, old: T, src: T) -> (T, bool);
  58     pub fn atomic_cxchg_relaxed<T>(dst: *mut T, old: T, src: T) -> (T, bool);
  59     pub fn atomic_cxchg_failrelaxed<T>(dst: *mut T, old: T, src: T) -> (T, bool);
  60     pub fn atomic_cxchg_failacq<T>(dst: *mut T, old: T, src: T) -> (T, bool);
  61     pub fn atomic_cxchg_acq_failrelaxed<T>(dst: *mut T, old: T, src: T) -> (T, bool);
  62     pub fn atomic_cxchg_acqrel_failrelaxed<T>(dst: *mut T, old: T, src: T) -> (T, bool);
  63
  64     pub fn atomic_cxchgweak<T>(dst: *mut T, old: T, src: T) -> (T, bool);
  65     pub fn atomic_cxchgweak_acq<T>(dst: *mut T, old: T, src: T) -> (T, bool);
  66     pub fn atomic_cxchgweak_rel<T>(dst: *mut T, old: T, src: T) -> (T, bool);
  67     pub fn atomic_cxchgweak_acqrel<T>(dst: *mut T, old: T, src: T) -> (T, bool);
  68     pub fn atomic_cxchgweak_relaxed<T>(dst: *mut T, old: T, src: T) -> (T, bool);
  69     pub fn atomic_cxchgweak_failrelaxed<T>(dst: *mut T, old: T, src: T) -> (T, bool);
  70     pub fn atomic_cxchgweak_failacq<T>(dst: *mut T, old: T, src: T) -> (T, bool);
  71     pub fn atomic_cxchgweak_acq_failrelaxed<T>(dst: *mut T, old: T, src: T) -> (T, bool);
  72     pub fn atomic_cxchgweak_acqrel_failrelaxed<T>(dst: *mut T, old: T, src: T) -> (T, bool);
  73
  74     pub fn atomic_load<T>(src: *const T) -> T;
  75     pub fn atomic_load_acq<T>(src: *const T) -> T;
  76     pub fn atomic_load_relaxed<T>(src: *const T) -> T;
  77     pub fn atomic_load_unordered<T>(src: *const T) -> T;
  78
  79     pub fn atomic_store<T>(dst: *mut T, val: T);
  80     pub fn atomic_store_rel<T>(dst: *mut T, val: T);
  81     pub fn atomic_store_relaxed<T>(dst: *mut T, val: T);
  82     pub fn atomic_store_unordered<T>(dst: *mut T, val: T);
  83
  84     pub fn atomic_xchg<T>(dst: *mut T, src: T) -> T;
  85     pub fn atomic_xchg_acq<T>(dst: *mut T, src: T) -> T;
  86     pub fn atomic_xchg_rel<T>(dst: *mut T, src: T) -> T;
  87     pub fn atomic_xchg_acqrel<T>(dst: *mut T, src: T) -> T;
  88     pub fn atomic_xchg_relaxed<T>(dst: *mut T, src: T) -> T;
  89
  90     pub fn atomic_xadd<T>(dst: *mut T, src: T) -> T;
  91     pub fn atomic_xadd_acq<T>(dst: *mut T, src: T) -> T;
  92     pub fn atomic_xadd_rel<T>(dst: *mut T, src: T) -> T;
  93     pub fn atomic_xadd_acqrel<T>(dst: *mut T, src: T) -> T;
  94     pub fn atomic_xadd_relaxed<T>(dst: *mut T, src: T) -> T;
  95
  96     pub fn atomic_xsub<T>(dst: *mut T, src: T) -> T;
  97     pub fn atomic_xsub_acq<T>(dst: *mut T, src: T) -> T;
  98     pub fn atomic_xsub_rel<T>(dst: *mut T, src: T) -> T;
  99     pub fn atomic_xsub_acqrel<T>(dst: *mut T, src: T) -> T;
 100     pub fn atomic_xsub_relaxed<T>(dst: *mut T, src: T) -> T;
 101
 102     pub fn atomic_and<T>(dst: *mut T, src: T) -> T;
 103     pub fn atomic_and_acq<T>(dst: *mut T, src: T) -> T;
 104     pub fn atomic_and_rel<T>(dst: *mut T, src: T) -> T;
 105     pub fn atomic_and_acqrel<T>(dst: *mut T, src: T) -> T;
 106     pub fn atomic_and_relaxed<T>(dst: *mut T, src: T) -> T;
 107
 108     pub fn atomic_nand<T>(dst: *mut T, src: T) -> T;
 109     pub fn atomic_nand_acq<T>(dst: *mut T, src: T) -> T;
 110     pub fn atomic_nand_rel<T>(dst: *mut T, src: T) -> T;
 111     pub fn atomic_nand_acqrel<T>(dst: *mut T, src: T) -> T;
 112     pub fn atomic_nand_relaxed<T>(dst: *mut T, src: T) -> T;
 113
 114     pub fn atomic_or<T>(dst: *mut T, src: T) -> T;
 115     pub fn atomic_or_acq<T>(dst: *mut T, src: T) -> T;
 116     pub fn atomic_or_rel<T>(dst: *mut T, src: T) -> T;
 117     pub fn atomic_or_acqrel<T>(dst: *mut T, src: T) -> T;
 118     pub fn atomic_or_relaxed<T>(dst: *mut T, src: T) -> T;
 119
 120     pub fn atomic_xor<T>(dst: *mut T, src: T) -> T;
 121     pub fn atomic_xor_acq<T>(dst: *mut T, src: T) -> T;
 122     pub fn atomic_xor_rel<T>(dst: *mut T, src: T) -> T;
 123     pub fn atomic_xor_acqrel<T>(dst: *mut T, src: T) -> T;
 124     pub fn atomic_xor_relaxed<T>(dst: *mut T, src: T) -> T;
 125
 126     pub fn atomic_max<T>(dst: *mut T, src: T) -> T;
 127     pub fn atomic_max_acq<T>(dst: *mut T, src: T) -> T;
 128     pub fn atomic_max_rel<T>(dst: *mut T, src: T) -> T;
 129     pub fn atomic_max_acqrel<T>(dst: *mut T, src: T) -> T;
 130     pub fn atomic_max_relaxed<T>(dst: *mut T, src: T) -> T;
 131
 132     pub fn atomic_min<T>(dst: *mut T, src: T) -> T;
 133     pub fn atomic_min_acq<T>(dst: *mut T, src: T) -> T;
 134     pub fn atomic_min_rel<T>(dst: *mut T, src: T) -> T;
 135     pub fn atomic_min_acqrel<T>(dst: *mut T, src: T) -> T;
 136     pub fn atomic_min_relaxed<T>(dst: *mut T, src: T) -> T;
 137
 138     pub fn atomic_umin<T>(dst: *mut T, src: T) -> T;
 139     pub fn atomic_umin_acq<T>(dst: *mut T, src: T) -> T;
 140     pub fn atomic_umin_rel<T>(dst: *mut T, src: T) -> T;
 141     pub fn atomic_umin_acqrel<T>(dst: *mut T, src: T) -> T;
 142     pub fn atomic_umin_relaxed<T>(dst: *mut T, src: T) -> T;
 143
 144     pub fn atomic_umax<T>(dst: *mut T, src: T) -> T;
 145     pub fn atomic_umax_acq<T>(dst: *mut T, src: T) -> T;
 146     pub fn atomic_umax_rel<T>(dst: *mut T, src: T) -> T;
 147     pub fn atomic_umax_acqrel<T>(dst: *mut T, src: T) -> T;
 148     pub fn atomic_umax_relaxed<T>(dst: *mut T, src: T) -> T;
 149 }
 150
 151 extern "rust-intrinsic" {
 152
 153     pub fn atomic_fence();
 154     pub fn atomic_fence_acq();
 155     pub fn atomic_fence_rel();
 156     pub fn atomic_fence_acqrel();
 157
 158     /// A compiler-only memory barrier.
 159     ///
 160     /// Memory accesses will never be reordered across this barrier by the
 161     /// compiler, but no instructions will be emitted for it. This is
 162     /// appropriate for operations on the same thread that may be preempted,
 163     /// such as when interacting with signal handlers.
 164     pub fn atomic_singlethreadfence();
 165     pub fn atomic_singlethreadfence_acq();
 166     pub fn atomic_singlethreadfence_rel();
 167     pub fn atomic_singlethreadfence_acqrel();
 168
 169     /// Magic intrinsic that derives its meaning from attributes
 170     /// attached to the function.
 171     ///
 172     /// For example, dataflow uses this to inject static assertions so
 173     /// that `rustc_peek(potentially_uninitialized)` would actually
 174     /// double-check that dataflow did indeed compute that it is
 175     /// uninitialized at that point in the control flow.
 176     pub fn rustc_peek<T>(_: T) -> T;
 177
 178     /// Aborts the execution of the process.
 179     pub fn abort() -> !;
 180
 181     /// Tells LLVM that this point in the code is not reachable,
 182     /// enabling further optimizations.
 183     ///
 184     /// NB: This is very different from the `unreachable!()` macro!
 185     pub fn unreachable() -> !;
 186
 187     /// Informs the optimizer that a condition is always true.
 188     /// If the condition is false, the behavior is undefined.
 189     ///
 190     /// No code is generated for this intrinsic, but the optimizer will try
 191     /// to preserve it (and its condition) between passes, which may interfere
 192     /// with optimization of surrounding code and reduce performance. It should
 193     /// not be used if the invariant can be discovered by the optimizer on its
 194     /// own, or if it does not enable any significant optimizations.
 195     pub fn assume(b: bool);
 196
 197     /// Hints to the compiler that branch condition is likely to be true.
 198     /// Returns the value passed to it.
 199     ///
 200     /// Any use other than with `if` statements will probably not have an effect.
 201     pub fn likely(b: bool) -> bool;
 202
 203     /// Hints to the compiler that branch condition is likely to be false.
 204     /// Returns the value passed to it.
 205     ///
 206     /// Any use other than with `if` statements will probably not have an effect.
 207     pub fn unlikely(b: bool) -> bool;
 208
 209     /// Executes a breakpoint trap, for inspection by a debugger.
 210     pub fn breakpoint();
 211
 212     /// The size of a type in bytes.
 213     ///
 214     /// More specifically, this is the offset in bytes between successive
 215     /// items of the same type, including alignment padding.
 216     pub fn size_of<T>() -> usize;
 217
 218     /// Moves a value to an uninitialized memory location.
 219     ///
 220     /// Drop glue is not run on the destination.
 221     pub fn move_val_init<T>(dst: *mut T, src: T);
 222
 223     pub fn min_align_of<T>() -> usize;
 224     pub fn pref_align_of<T>() -> usize;
 225
 226     pub fn size_of_val<T: ?Sized>(_: &T) -> usize;
 227     pub fn min_align_of_val<T: ?Sized>(_: &T) -> usize;
 228
 229     /// Executes the destructor (if any) of the pointed-to value.
 230     ///
 231     /// This has two use cases:
 232     ///
 233     /// * It is *required* to use `drop_in_place` to drop unsized types like
 234     ///   trait objects, because they can't be read out onto the stack and
 235     ///   dropped normally.
 236     ///
 237     /// * It is friendlier to the optimizer to do this over `ptr::read` when
 238     ///   dropping manually allocated memory (e.g. when writing Box/Rc/Vec),
 239     ///   as the compiler doesn't need to prove that it's sound to elide the
 240     ///   copy.
 241     ///
 242     /// # Undefined Behavior
 243     ///
 244     /// This has all the same safety problems as `ptr::read` with respect to
 245     /// invalid pointers, types, and double drops.
 246     #[stable(feature = "drop_in_place", since = "1.8.0")]
 247     pub fn drop_in_place<T: ?Sized>(to_drop: *mut T);
 248
 249     /// Gets a static string slice containing the name of a type.
 250     pub fn type_name<T: ?Sized>() -> &'static str;
 251
 252     /// Gets an identifier which is globally unique to the specified type. This
 253     /// function will return the same value for a type regardless of whichever
 254     /// crate it is invoked in.
 255     pub fn type_id<T: ?Sized + 'static>() -> u64;
 256
 257     /// Creates a value initialized to zero.
 258     ///
 259     /// `init` is unsafe because it returns a zeroed-out datum,
 260     /// which is unsafe unless T is `Copy`.  Also, even if T is
 261     /// `Copy`, an all-zero value may not correspond to any legitimate
 262     /// state for the type in question.
 263     pub fn init<T>() -> T;
 264
 265     /// Creates an uninitialized value.
 266     ///
 267     /// `uninit` is unsafe because there is no guarantee of what its
 268     /// contents are. In particular its drop-flag may be set to any
 269     /// state, which means it may claim either dropped or
 270     /// undropped. In the general case one must use `ptr::write` to
 271     /// initialize memory previous set to the result of `uninit`.
 272     pub fn uninit<T>() -> T;
 273
 274     /// Moves a value out of scope without running drop glue.
 275     pub fn forget<T>(_: T) -> ();
 276
 277     /// Reinterprets the bits of a value of one type as another type.
 278     ///
 279     /// Both types must have the same size. Neither the original, nor the result,
 280     /// may be an [invalid value](../../nomicon/meet-safe-and-unsafe.html).
 281     ///
 282     /// `transmute` is semantically equivalent to a bitwise move of one type
 283     /// into another. It copies the bits from the source value into the
 284     /// destination value, then forgets the original. It's equivalent to C's
 285     /// `memcpy` under the hood, just like `transmute_copy`.
 286     ///
 287     /// `transmute` is **incredibly** unsafe. There are a vast number of ways to
 288     /// cause [undefined behavior][ub] with this function. `transmute` should be
 289     /// the absolute last resort.
 290     ///
 291     /// The [nomicon](../../nomicon/transmutes.html) has additional
 292     /// documentation.
 293     ///
 294     /// [ub]: ../../reference.html#behavior-considered-undefined
 295     ///
 296     /// # Examples
 297     ///
 298     /// There are a few things that `transmute` is really useful for.
 299     ///
 300     /// Getting the bitpattern of a floating point type (or, more generally,
 301     /// type punning, when `T` and `U` aren't pointers):
 302     ///
 303     /// ```
 304     /// let bitpattern = unsafe {
 305     ///     std::mem::transmute::<f32, u32>(1.0)
 306     /// };
 307     /// assert_eq!(bitpattern, 0x3F800000);
 308     /// ```
 309     ///
 310     /// Turning a pointer into a function pointer. This is *not* portable to
 311     /// machines where function pointers and data pointers have different sizes.
 312     ///
 313     /// ```
 314     /// fn foo() -> i32 {
 315     ///     0
 316     /// }
 317     /// let pointer = foo as *const ();
 318     /// let function = unsafe {
 319     ///     std::mem::transmute::<*const (), fn() -> i32>(pointer)
 320     /// };
 321     /// assert_eq!(function(), 0);
 322     /// ```
 323     ///
 324     /// Extending a lifetime, or shortening an invariant lifetime. This is
 325     /// advanced, very unsafe Rust!
 326     ///
 327     /// ```
 328     /// struct R<'a>(&'a i32);
 329     /// unsafe fn extend_lifetime<'b>(r: R<'b>) -> R<'static> {
 330     ///     std::mem::transmute::<R<'b>, R<'static>>(r)
 331     /// }
 332     ///
 333     /// unsafe fn shorten_invariant_lifetime<'b, 'c>(r: &'b mut R<'static>)
 334     ///                                              -> &'b mut R<'c> {
 335     ///     std::mem::transmute::<&'b mut R<'static>, &'b mut R<'c>>(r)
 336     /// }
 337     /// ```
 338     ///
 339     /// # Alternatives
 340     ///
 341     /// Don't despair: many uses of `transmute` can be achieved through other means.
 342     /// Below are common applications of `transmute` which can be replaced with safer
 343     /// constructs.
 344     ///
 345     /// Turning a pointer into a `usize`:
 346     ///
 347     /// ```
 348     /// let ptr = &0;
 349     /// let ptr_num_transmute = unsafe {
 350     ///     std::mem::transmute::<&i32, usize>(ptr)
 351     /// };
 352     ///
 353     /// // Use an `as` cast instead
 354     /// let ptr_num_cast = ptr as *const i32 as usize;
 355     /// ```
 356     ///
 357     /// Turning a `*mut T` into an `&mut T`:
 358     ///
 359     /// ```
 360     /// let ptr: *mut i32 = &mut 0;
 361     /// let ref_transmuted = unsafe {
 362     ///     std::mem::transmute::<*mut i32, &mut i32>(ptr)
 363     /// };
 364     ///
 365     /// // Use a reborrow instead
 366     /// let ref_casted = unsafe { &mut *ptr };
 367     /// ```
 368     ///
 369     /// Turning an `&mut T` into an `&mut U`:
 370     ///
 371     /// ```
 372     /// let ptr = &mut 0;
 373     /// let val_transmuted = unsafe {
 374     ///     std::mem::transmute::<&mut i32, &mut u32>(ptr)
 375     /// };
 376     ///
 377     /// // Now, put together `as` and reborrowing - note the chaining of `as`
 378     /// // `as` is not transitive
 379     /// let val_casts = unsafe { &mut *(ptr as *mut i32 as *mut u32) };
 380     /// ```
 381     ///
 382     /// Turning an `&str` into an `&[u8]`:
 383     ///
 384     /// ```
 385     /// // this is not a good way to do this.
 386     /// let slice = unsafe { std::mem::transmute::<&str, &[u8]>("Rust") };
 387     /// assert_eq!(slice, &[82, 117, 115, 116]);
 388     ///
 389     /// // You could use `str::as_bytes`
 390     /// let slice = "Rust".as_bytes();
 391     /// assert_eq!(slice, &[82, 117, 115, 116]);
 392     ///
 393     /// // Or, just use a byte string, if you have control over the string
 394     /// // literal
 395     /// assert_eq!(b"Rust", &[82, 117, 115, 116]);
 396     /// ```
 397     ///
 398     /// Turning a `Vec<&T>` into a `Vec<Option<&T>>`:
 399     ///
 400     /// ```
 401     /// let store = [0, 1, 2, 3];
 402     /// let mut v_orig = store.iter().collect::<Vec<&i32>>();
 403     ///
 404     /// // Using transmute: this is Undefined Behavior, and a bad idea.
 405     /// // However, it is no-copy.
 406     /// let v_transmuted = unsafe {
 407     ///     std::mem::transmute::<Vec<&i32>, Vec<Option<&i32>>>(
 408     ///         v_orig.clone())
 409     /// };
 410     ///
 411     /// // This is the suggested, safe way.
 412     /// // It does copy the entire vector, though, into a new array.
 413     /// let v_collected = v_orig.clone()
 414     ///                         .into_iter()
 415     ///                         .map(|r| Some(r))
 416     ///                         .collect::<Vec<Option<&i32>>>();
 417     ///
 418     /// // The no-copy, unsafe way, still using transmute, but not UB.
 419     /// // This is equivalent to the original, but safer, and reuses the
 420     /// // same Vec internals. Therefore the new inner type must have the
 421     /// // exact same size, and the same or lesser alignment, as the old
 422     /// // type. The same caveats exist for this method as transmute, for
 423     /// // the original inner type (`&i32`) to the converted inner type
 424     /// // (`Option<&i32>`), so read the nomicon pages linked above.
 425     /// let v_from_raw = unsafe {
 426     ///     Vec::from_raw_parts(v_orig.as_mut_ptr(),
 427     ///                         v_orig.len(),
 428     ///                         v_orig.capacity())
 429     /// };
 430     /// std::mem::forget(v_orig);
 431     /// ```
 432     ///
 433     /// Implementing `split_at_mut`:
 434     ///
 435     /// ```
 436     /// use std::{slice, mem};
 437     ///
 438     /// // There are multiple ways to do this; and there are multiple problems
 439     /// // with the following, transmute, way.
 440     /// fn split_at_mut_transmute<T>(slice: &mut [T], mid: usize)
 441     ///                              -> (&mut [T], &mut [T]) {
 442     ///     let len = slice.len();
 443     ///     assert!(mid <= len);
 444     ///     unsafe {
 445     ///         let slice2 = mem::transmute::<&mut [T], &mut [T]>(slice);
 446     ///         // first: transmute is not typesafe; all it checks is that T and
 447     ///         // U are of the same size. Second, right here, you have two
 448     ///         // mutable references pointing to the same memory.
 449     ///         (&mut slice[0..mid], &mut slice2[mid..len])
 450     ///     }
 451     /// }
 452     ///
 453     /// // This gets rid of the typesafety problems; `&mut *` will *only* give
 454     /// // you an `&mut T` from an `&mut T` or `*mut T`.
 455     /// fn split_at_mut_casts<T>(slice: &mut [T], mid: usize)
 456     ///                          -> (&mut [T], &mut [T]) {
 457     ///     let len = slice.len();
 458     ///     assert!(mid <= len);
 459     ///     unsafe {
 460     ///         let slice2 = &mut *(slice as *mut [T]);
 461     ///         // however, you still have two mutable references pointing to
 462     ///         // the same memory.
 463     ///         (&mut slice[0..mid], &mut slice2[mid..len])
 464     ///     }
 465     /// }
 466     ///
 467     /// // This is how the standard library does it. This is the best method, if
 468     /// // you need to do something like this
 469     /// fn split_at_stdlib<T>(slice: &mut [T], mid: usize)
 470     ///                       -> (&mut [T], &mut [T]) {
 471     ///     let len = slice.len();
 472     ///     assert!(mid <= len);
 473     ///     unsafe {
 474     ///         let ptr = slice.as_mut_ptr();
 475     ///         // This now has three mutable references pointing at the same
 476     ///         // memory. `slice`, the rvalue ret.0, and the rvalue ret.1.
 477     ///         // `slice` is never used after `let ptr = ...`, and so one can
 478     ///         // treat it as "dead", and therefore, you only have two real
 479     ///         // mutable slices.
 480     ///         (slice::from_raw_parts_mut(ptr, mid),
 481     ///          slice::from_raw_parts_mut(ptr.offset(mid as isize), len - mid))
 482     ///     }
 483     /// }
 484     /// ```
 485     #[stable(feature = "rust1", since = "1.0.0")]
 486     pub fn transmute<T, U>(e: T) -> U;
 487
 488     /// Returns `true` if the actual type given as `T` requires drop
 489     /// glue; returns `false` if the actual type provided for `T`
 490     /// implements `Copy`.
 491     ///
 492     /// If the actual type neither requires drop glue nor implements
 493     /// `Copy`, then may return `true` or `false`.
 494     pub fn needs_drop<T>() -> bool;
 495
 496     /// Calculates the offset from a pointer.
 497     ///
 498     /// This is implemented as an intrinsic to avoid converting to and from an
 499     /// integer, since the conversion would throw away aliasing information.
 500     ///
 501     /// # Safety
 502     ///
 503     /// Both the starting and resulting pointer must be either in bounds or one
 504     /// byte past the end of an allocated object. If either pointer is out of
 505     /// bounds or arithmetic overflow occurs then any further use of the
 506     /// returned value will result in undefined behavior.
 507     pub fn offset<T>(dst: *const T, offset: isize) -> *const T;
 508
 509     /// Calculates the offset from a pointer, potentially wrapping.
 510     ///
 511     /// This is implemented as an intrinsic to avoid converting to and from an
 512     /// integer, since the conversion inhibits certain optimizations.
 513     ///
 514     /// # Safety
 515     ///
 516     /// Unlike the `offset` intrinsic, this intrinsic does not restrict the
 517     /// resulting pointer to point into or one byte past the end of an allocated
 518     /// object, and it wraps with two's complement arithmetic. The resulting
 519     /// value is not necessarily valid to be used to actually access memory.
 520     pub fn arith_offset<T>(dst: *const T, offset: isize) -> *const T;
 521
 522     /// Copies `count * size_of<T>` bytes from `src` to `dst`. The source
 523     /// and destination may *not* overlap.
 524     ///
 525     /// `copy_nonoverlapping` is semantically equivalent to C's `memcpy`.
 526     ///
 527     /// # Safety
 528     ///
 529     /// Beyond requiring that the program must be allowed to access both regions
 530     /// of memory, it is Undefined Behavior for source and destination to
 531     /// overlap. Care must also be taken with the ownership of `src` and
 532     /// `dst`. This method semantically moves the values of `src` into `dst`.
 533     /// However it does not drop the contents of `dst`, or prevent the contents
 534     /// of `src` from being dropped or used.
 535     ///
 536     /// # Examples
 537     ///
 538     /// A safe swap function:
 539     ///
 540     /// ```
 541     /// use std::mem;
 542     /// use std::ptr;
 543     ///
 544     /// # #[allow(dead_code)]
 545     /// fn swap<T>(x: &mut T, y: &mut T) {
 546     ///     unsafe {
 547     ///         // Give ourselves some scratch space to work with
 548     ///         let mut t: T = mem::uninitialized();
 549     ///
 550     ///         // Perform the swap, `&mut` pointers never alias
 551     ///         ptr::copy_nonoverlapping(x, &mut t, 1);
 552     ///         ptr::copy_nonoverlapping(y, x, 1);
 553     ///         ptr::copy_nonoverlapping(&t, y, 1);
 554     ///
 555     ///         // y and t now point to the same thing, but we need to completely forget `tmp`
 556     ///         // because it's no longer relevant.
 557     ///         mem::forget(t);
 558     ///     }
 559     /// }
 560     /// ```
 561     #[stable(feature = "rust1", since = "1.0.0")]
 562     pub fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
 563
 564     /// Copies `count * size_of<T>` bytes from `src` to `dst`. The source
 565     /// and destination may overlap.
 566     ///
 567     /// `copy` is semantically equivalent to C's `memmove`.
 568     ///
 569     /// # Safety
 570     ///
 571     /// Care must be taken with the ownership of `src` and `dst`.
 572     /// This method semantically moves the values of `src` into `dst`.
 573     /// However it does not drop the contents of `dst`, or prevent the contents of `src`
 574     /// from being dropped or used.
 575     ///
 576     /// # Examples
 577     ///
 578     /// Efficiently create a Rust vector from an unsafe buffer:
 579     ///
 580     /// ```
 581     /// use std::ptr;
 582     ///
 583     /// # #[allow(dead_code)]
 584     /// unsafe fn from_buf_raw<T>(ptr: *const T, elts: usize) -> Vec<T> {
 585     ///     let mut dst = Vec::with_capacity(elts);
 586     ///     dst.set_len(elts);
 587     ///     ptr::copy(ptr, dst.as_mut_ptr(), elts);
 588     ///     dst
 589     /// }
 590     /// ```
 591     ///
 592     #[stable(feature = "rust1", since = "1.0.0")]
 593     pub fn copy<T>(src: *const T, dst: *mut T, count: usize);
 594
 595     /// Invokes memset on the specified pointer, setting `count * size_of::<T>()`
 596     /// bytes of memory starting at `dst` to `val`.
 597     ///
 598     /// # Examples
 599     ///
 600     /// ```
 601     /// use std::ptr;
 602     ///
 603     /// let mut vec = vec![0; 4];
 604     /// unsafe {
 605     ///     let vec_ptr = vec.as_mut_ptr();
 606     ///     ptr::write_bytes(vec_ptr, b'a', 2);
 607     /// }
 608     /// assert_eq!(vec, [b'a', b'a', 0, 0]);
 609     /// ```
 610     #[stable(feature = "rust1", since = "1.0.0")]
 611     pub fn write_bytes<T>(dst: *mut T, val: u8, count: usize);
 612
 613     /// Equivalent to the appropriate `llvm.memcpy.p0i8.0i8.*` intrinsic, with
 614     /// a size of `count` * `size_of::<T>()` and an alignment of
 615     /// `min_align_of::<T>()`
 616     ///
 617     /// The volatile parameter is set to `true`, so it will not be optimized out.
 618     pub fn volatile_copy_nonoverlapping_memory<T>(dst: *mut T, src: *const T,
 619                                                   count: usize);
 620     /// Equivalent to the appropriate `llvm.memmove.p0i8.0i8.*` intrinsic, with
 621     /// a size of `count` * `size_of::<T>()` and an alignment of
 622     /// `min_align_of::<T>()`
 623     ///
 624     /// The volatile parameter is set to `true`, so it will not be optimized out.
 625     pub fn volatile_copy_memory<T>(dst: *mut T, src: *const T, count: usize);
 626     /// Equivalent to the appropriate `llvm.memset.p0i8.*` intrinsic, with a
 627     /// size of `count` * `size_of::<T>()` and an alignment of
 628     /// `min_align_of::<T>()`.
 629     ///
 630     /// The volatile parameter is set to `true`, so it will not be optimized out.
 631     pub fn volatile_set_memory<T>(dst: *mut T, val: u8, count: usize);
 632
 633     /// Perform a volatile load from the `src` pointer.
 634     pub fn volatile_load<T>(src: *const T) -> T;
 635     /// Perform a volatile store to the `dst` pointer.
 636     pub fn volatile_store<T>(dst: *mut T, val: T);
 637
 638     /// Returns the square root of an `f32`
 639     pub fn sqrtf32(x: f32) -> f32;
 640     /// Returns the square root of an `f64`
 641     pub fn sqrtf64(x: f64) -> f64;
 642
 643     /// Raises an `f32` to an integer power.
 644     pub fn powif32(a: f32, x: i32) -> f32;
 645     /// Raises an `f64` to an integer power.
 646     pub fn powif64(a: f64, x: i32) -> f64;
 647
 648     /// Returns the sine of an `f32`.
 649     pub fn sinf32(x: f32) -> f32;
 650     /// Returns the sine of an `f64`.
 651     pub fn sinf64(x: f64) -> f64;
 652
 653     /// Returns the cosine of an `f32`.
 654     pub fn cosf32(x: f32) -> f32;
 655     /// Returns the cosine of an `f64`.
 656     pub fn cosf64(x: f64) -> f64;
 657
 658     /// Raises an `f32` to an `f32` power.
 659     pub fn powf32(a: f32, x: f32) -> f32;
 660     /// Raises an `f64` to an `f64` power.
 661     pub fn powf64(a: f64, x: f64) -> f64;
 662
 663     /// Returns the exponential of an `f32`.
 664     pub fn expf32(x: f32) -> f32;
 665     /// Returns the exponential of an `f64`.
 666     pub fn expf64(x: f64) -> f64;
 667
 668     /// Returns 2 raised to the power of an `f32`.
 669     pub fn exp2f32(x: f32) -> f32;
 670     /// Returns 2 raised to the power of an `f64`.
 671     pub fn exp2f64(x: f64) -> f64;
 672
 673     /// Returns the natural logarithm of an `f32`.
 674     pub fn logf32(x: f32) -> f32;
 675     /// Returns the natural logarithm of an `f64`.
 676     pub fn logf64(x: f64) -> f64;
 677
 678     /// Returns the base 10 logarithm of an `f32`.
 679     pub fn log10f32(x: f32) -> f32;
 680     /// Returns the base 10 logarithm of an `f64`.
 681     pub fn log10f64(x: f64) -> f64;
 682
 683     /// Returns the base 2 logarithm of an `f32`.
 684     pub fn log2f32(x: f32) -> f32;
 685     /// Returns the base 2 logarithm of an `f64`.
 686     pub fn log2f64(x: f64) -> f64;
 687
 688     /// Returns `a * b + c` for `f32` values.
 689     pub fn fmaf32(a: f32, b: f32, c: f32) -> f32;
 690     /// Returns `a * b + c` for `f64` values.
 691     pub fn fmaf64(a: f64, b: f64, c: f64) -> f64;
 692
 693     /// Returns the absolute value of an `f32`.
 694     pub fn fabsf32(x: f32) -> f32;
 695     /// Returns the absolute value of an `f64`.
 696     pub fn fabsf64(x: f64) -> f64;
 697
 698     /// Copies the sign from `y` to `x` for `f32` values.
 699     pub fn copysignf32(x: f32, y: f32) -> f32;
 700     /// Copies the sign from `y` to `x` for `f64` values.
 701     pub fn copysignf64(x: f64, y: f64) -> f64;
 702
 703     /// Returns the largest integer less than or equal to an `f32`.
 704     pub fn floorf32(x: f32) -> f32;
 705     /// Returns the largest integer less than or equal to an `f64`.
 706     pub fn floorf64(x: f64) -> f64;
 707
 708     /// Returns the smallest integer greater than or equal to an `f32`.
 709     pub fn ceilf32(x: f32) -> f32;
 710     /// Returns the smallest integer greater than or equal to an `f64`.
 711     pub fn ceilf64(x: f64) -> f64;
 712
 713     /// Returns the integer part of an `f32`.
 714     pub fn truncf32(x: f32) -> f32;
 715     /// Returns the integer part of an `f64`.
 716     pub fn truncf64(x: f64) -> f64;
 717
 718     /// Returns the nearest integer to an `f32`. May raise an inexact floating-point exception
 719     /// if the argument is not an integer.
 720     pub fn rintf32(x: f32) -> f32;
 721     /// Returns the nearest integer to an `f64`. May raise an inexact floating-point exception
 722     /// if the argument is not an integer.
 723     pub fn rintf64(x: f64) -> f64;
 724
 725     /// Returns the nearest integer to an `f32`.
 726     pub fn nearbyintf32(x: f32) -> f32;
 727     /// Returns the nearest integer to an `f64`.
 728     pub fn nearbyintf64(x: f64) -> f64;
 729
 730     /// Returns the nearest integer to an `f32`. Rounds half-way cases away from zero.
 731     pub fn roundf32(x: f32) -> f32;
 732     /// Returns the nearest integer to an `f64`. Rounds half-way cases away from zero.
 733     pub fn roundf64(x: f64) -> f64;
 734
 735     /// Float addition that allows optimizations based on algebraic rules.
 736     /// May assume inputs are finite.
 737     pub fn fadd_fast<T>(a: T, b: T) -> T;
 738
 739     /// Float subtraction that allows optimizations based on algebraic rules.
 740     /// May assume inputs are finite.
 741     pub fn fsub_fast<T>(a: T, b: T) -> T;
 742
 743     /// Float multiplication that allows optimizations based on algebraic rules.
 744     /// May assume inputs are finite.
 745     pub fn fmul_fast<T>(a: T, b: T) -> T;
 746
 747     /// Float division that allows optimizations based on algebraic rules.
 748     /// May assume inputs are finite.
 749     pub fn fdiv_fast<T>(a: T, b: T) -> T;
 750
 751     /// Float remainder that allows optimizations based on algebraic rules.
 752     /// May assume inputs are finite.
 753     pub fn frem_fast<T>(a: T, b: T) -> T;
 754
 755
 756     /// Returns the number of bits set in an integer type `T`
 757     pub fn ctpop<T>(x: T) -> T;
 758
 759     /// Returns the number of leading bits unset in an integer type `T`
 760     pub fn ctlz<T>(x: T) -> T;
 761
 762     /// Returns the number of trailing bits unset in an integer type `T`
 763     pub fn cttz<T>(x: T) -> T;
 764
 765     /// Reverses the bytes in an integer type `T`.
 766     pub fn bswap<T>(x: T) -> T;
 767
 768     /// Performs checked integer addition.
 769     pub fn add_with_overflow<T>(x: T, y: T) -> (T, bool);
 770
 771     /// Performs checked integer subtraction
 772     pub fn sub_with_overflow<T>(x: T, y: T) -> (T, bool);
 773
 774     /// Performs checked integer multiplication
 775     pub fn mul_with_overflow<T>(x: T, y: T) -> (T, bool);
 776
 777     /// Performs an unchecked division, resulting in undefined behavior
 778     /// where y = 0 or x = `T::min_value()` and y = -1
 779     pub fn unchecked_div<T>(x: T, y: T) -> T;
 780     /// Returns the remainder of an unchecked division, resulting in
 781     /// undefined behavior where y = 0 or x = `T::min_value()` and y = -1
 782     pub fn unchecked_rem<T>(x: T, y: T) -> T;
 783
 784     /// Returns (a + b) mod 2^N, where N is the width of T in bits.
 785     pub fn overflowing_add<T>(a: T, b: T) -> T;
 786     /// Returns (a - b) mod 2^N, where N is the width of T in bits.
 787     pub fn overflowing_sub<T>(a: T, b: T) -> T;
 788     /// Returns (a * b) mod 2^N, where N is the width of T in bits.
 789     pub fn overflowing_mul<T>(a: T, b: T) -> T;
 790
 791     /// Returns the value of the discriminant for the variant in 'v',
 792     /// cast to a `u64`; if `T` has no discriminant, returns 0.
 793     pub fn discriminant_value<T>(v: &T) -> u64;
 794
 795     /// Rust's "try catch" construct which invokes the function pointer `f` with
 796     /// the data pointer `data`.
 797     ///
 798     /// The third pointer is a target-specific data pointer which is filled in
 799     /// with the specifics of the exception that occurred. For examples on Unix
 800     /// platforms this is a `*mut *mut T` which is filled in by the compiler and
 801     /// on MSVC it's `*mut [usize; 2]`. For more information see the compiler's
 802     /// source as well as std's catch implementation.
 803     pub fn try(f: fn(*mut u8), data: *mut u8, local_ptr: *mut u8) -> i32;
 804 }