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/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")]
  43 #![allow(missing_docs)]
  44
  45 use marker::Sized;
  46
  47 extern "rust-intrinsic" {
  48
  49     // NB: These intrinsics take unsafe pointers because they mutate aliased
  50     // memory, which is not valid for either `&` or `&mut`.
  51
  52     pub fn atomic_cxchg<T>(dst: *mut T, old: T, src: T) -> T;
  53     pub fn atomic_cxchg_acq<T>(dst: *mut T, old: T, src: T) -> T;
  54     pub fn atomic_cxchg_rel<T>(dst: *mut T, old: T, src: T) -> T;
  55     pub fn atomic_cxchg_acqrel<T>(dst: *mut T, old: T, src: T) -> T;
  56     pub fn atomic_cxchg_relaxed<T>(dst: *mut T, old: T, src: T) -> T;
  57
  58     pub fn atomic_load<T>(src: *const T) -> T;
  59     pub fn atomic_load_acq<T>(src: *const T) -> T;
  60     pub fn atomic_load_relaxed<T>(src: *const T) -> T;
  61     pub fn atomic_load_unordered<T>(src: *const T) -> T;
  62
  63     pub fn atomic_store<T>(dst: *mut T, val: T);
  64     pub fn atomic_store_rel<T>(dst: *mut T, val: T);
  65     pub fn atomic_store_relaxed<T>(dst: *mut T, val: T);
  66     pub fn atomic_store_unordered<T>(dst: *mut T, val: T);
  67
  68     pub fn atomic_xchg<T>(dst: *mut T, src: T) -> T;
  69     pub fn atomic_xchg_acq<T>(dst: *mut T, src: T) -> T;
  70     pub fn atomic_xchg_rel<T>(dst: *mut T, src: T) -> T;
  71     pub fn atomic_xchg_acqrel<T>(dst: *mut T, src: T) -> T;
  72     pub fn atomic_xchg_relaxed<T>(dst: *mut T, src: T) -> T;
  73
  74     pub fn atomic_xadd<T>(dst: *mut T, src: T) -> T;
  75     pub fn atomic_xadd_acq<T>(dst: *mut T, src: T) -> T;
  76     pub fn atomic_xadd_rel<T>(dst: *mut T, src: T) -> T;
  77     pub fn atomic_xadd_acqrel<T>(dst: *mut T, src: T) -> T;
  78     pub fn atomic_xadd_relaxed<T>(dst: *mut T, src: T) -> T;
  79
  80     pub fn atomic_xsub<T>(dst: *mut T, src: T) -> T;
  81     pub fn atomic_xsub_acq<T>(dst: *mut T, src: T) -> T;
  82     pub fn atomic_xsub_rel<T>(dst: *mut T, src: T) -> T;
  83     pub fn atomic_xsub_acqrel<T>(dst: *mut T, src: T) -> T;
  84     pub fn atomic_xsub_relaxed<T>(dst: *mut T, src: T) -> T;
  85
  86     pub fn atomic_and<T>(dst: *mut T, src: T) -> T;
  87     pub fn atomic_and_acq<T>(dst: *mut T, src: T) -> T;
  88     pub fn atomic_and_rel<T>(dst: *mut T, src: T) -> T;
  89     pub fn atomic_and_acqrel<T>(dst: *mut T, src: T) -> T;
  90     pub fn atomic_and_relaxed<T>(dst: *mut T, src: T) -> T;
  91
  92     pub fn atomic_nand<T>(dst: *mut T, src: T) -> T;
  93     pub fn atomic_nand_acq<T>(dst: *mut T, src: T) -> T;
  94     pub fn atomic_nand_rel<T>(dst: *mut T, src: T) -> T;
  95     pub fn atomic_nand_acqrel<T>(dst: *mut T, src: T) -> T;
  96     pub fn atomic_nand_relaxed<T>(dst: *mut T, src: T) -> T;
  97
  98     pub fn atomic_or<T>(dst: *mut T, src: T) -> T;
  99     pub fn atomic_or_acq<T>(dst: *mut T, src: T) -> T;
 100     pub fn atomic_or_rel<T>(dst: *mut T, src: T) -> T;
 101     pub fn atomic_or_acqrel<T>(dst: *mut T, src: T) -> T;
 102     pub fn atomic_or_relaxed<T>(dst: *mut T, src: T) -> T;
 103
 104     pub fn atomic_xor<T>(dst: *mut T, src: T) -> T;
 105     pub fn atomic_xor_acq<T>(dst: *mut T, src: T) -> T;
 106     pub fn atomic_xor_rel<T>(dst: *mut T, src: T) -> T;
 107     pub fn atomic_xor_acqrel<T>(dst: *mut T, src: T) -> T;
 108     pub fn atomic_xor_relaxed<T>(dst: *mut T, src: T) -> T;
 109
 110     pub fn atomic_max<T>(dst: *mut T, src: T) -> T;
 111     pub fn atomic_max_acq<T>(dst: *mut T, src: T) -> T;
 112     pub fn atomic_max_rel<T>(dst: *mut T, src: T) -> T;
 113     pub fn atomic_max_acqrel<T>(dst: *mut T, src: T) -> T;
 114     pub fn atomic_max_relaxed<T>(dst: *mut T, src: T) -> T;
 115
 116     pub fn atomic_min<T>(dst: *mut T, src: T) -> T;
 117     pub fn atomic_min_acq<T>(dst: *mut T, src: T) -> T;
 118     pub fn atomic_min_rel<T>(dst: *mut T, src: T) -> T;
 119     pub fn atomic_min_acqrel<T>(dst: *mut T, src: T) -> T;
 120     pub fn atomic_min_relaxed<T>(dst: *mut T, src: T) -> T;
 121
 122     pub fn atomic_umin<T>(dst: *mut T, src: T) -> T;
 123     pub fn atomic_umin_acq<T>(dst: *mut T, src: T) -> T;
 124     pub fn atomic_umin_rel<T>(dst: *mut T, src: T) -> T;
 125     pub fn atomic_umin_acqrel<T>(dst: *mut T, src: T) -> T;
 126     pub fn atomic_umin_relaxed<T>(dst: *mut T, src: T) -> T;
 127
 128     pub fn atomic_umax<T>(dst: *mut T, src: T) -> T;
 129     pub fn atomic_umax_acq<T>(dst: *mut T, src: T) -> T;
 130     pub fn atomic_umax_rel<T>(dst: *mut T, src: T) -> T;
 131     pub fn atomic_umax_acqrel<T>(dst: *mut T, src: T) -> T;
 132     pub fn atomic_umax_relaxed<T>(dst: *mut T, src: T) -> T;
 133 }
 134
 135 extern "rust-intrinsic" {
 136
 137     pub fn atomic_fence();
 138     pub fn atomic_fence_acq();
 139     pub fn atomic_fence_rel();
 140     pub fn atomic_fence_acqrel();
 141
 142     /// A compiler-only memory barrier.
 143     ///
 144     /// Memory accesses will never be reordered across this barrier by the compiler,
 145     /// but no instructions will be emitted for it. This is appropriate for operations
 146     /// on the same thread that may be preempted, such as when interacting with signal
 147     /// handlers.
 148     #[cfg(not(stage0))]     // SNAP 857ef6e
 149     pub fn atomic_singlethreadfence();
 150     #[cfg(not(stage0))]     // SNAP 857ef6e
 151     pub fn atomic_singlethreadfence_acq();
 152     #[cfg(not(stage0))]     // SNAP 857ef6e
 153     pub fn atomic_singlethreadfence_rel();
 154     #[cfg(not(stage0))]     // SNAP 857ef6e
 155     pub fn atomic_singlethreadfence_acqrel();
 156
 157     /// Aborts the execution of the process.
 158     pub fn abort() -> !;
 159
 160     /// Tells LLVM that this point in the code is not reachable,
 161     /// enabling further optimizations.
 162     ///
 163     /// NB: This is very different from the `unreachable!()` macro!
 164     pub fn unreachable() -> !;
 165
 166     /// Informs the optimizer that a condition is always true.
 167     /// If the condition is false, the behavior is undefined.
 168     ///
 169     /// No code is generated for this intrinsic, but the optimizer will try
 170     /// to preserve it (and its condition) between passes, which may interfere
 171     /// with optimization of surrounding code and reduce performance. It should
 172     /// not be used if the invariant can be discovered by the optimizer on its
 173     /// own, or if it does not enable any significant optimizations.
 174     pub fn assume(b: bool);
 175
 176     /// Executes a breakpoint trap, for inspection by a debugger.
 177     pub fn breakpoint();
 178
 179     /// The size of a type in bytes.
 180     ///
 181     /// This is the exact number of bytes in memory taken up by a
 182     /// value of the given type. In other words, a memset of this size
 183     /// would *exactly* overwrite a value. When laid out in vectors
 184     /// and structures there may be additional padding between
 185     /// elements.
 186     pub fn size_of<T>() -> usize;
 187
 188     /// Moves a value to an uninitialized memory location.
 189     ///
 190     /// Drop glue is not run on the destination.
 191     pub fn move_val_init<T>(dst: &mut T, src: T);
 192
 193     pub fn min_align_of<T>() -> usize;
 194     pub fn pref_align_of<T>() -> usize;
 195
 196     #[cfg(not(stage0))]
 197     pub fn size_of_val<T: ?Sized>(_: &T) -> usize;
 198     #[cfg(not(stage0))]
 199     pub fn min_align_of_val<T: ?Sized>(_: &T) -> usize;
 200     #[cfg(not(stage0))]
 201     pub fn drop_in_place<T: ?Sized>(_: *mut T);
 202
 203     /// Gets a static string slice containing the name of a type.
 204     pub fn type_name<T: ?Sized>() -> &'static str;
 205
 206     /// Gets an identifier which is globally unique to the specified type. This
 207     /// function will return the same value for a type regardless of whichever
 208     /// crate it is invoked in.
 209     pub fn type_id<T: ?Sized + 'static>() -> u64;
 210
 211     /// Creates a value initialized to so that its drop flag,
 212     /// if any, says that it has been dropped.
 213     ///
 214     /// `init_dropped` is unsafe because it returns a datum with all
 215     /// of its bytes set to the drop flag, which generally does not
 216     /// correspond to a valid value.
 217     ///
 218     /// This intrinsic is likely to be deprecated in the future when
 219     /// Rust moves to non-zeroing dynamic drop (and thus removes the
 220     /// embedded drop flags that are being established by this
 221     /// intrinsic).
 222     pub fn init_dropped<T>() -> T;
 223
 224     /// Creates a value initialized to zero.
 225     ///
 226     /// `init` is unsafe because it returns a zeroed-out datum,
 227     /// which is unsafe unless T is `Copy`.  Also, even if T is
 228     /// `Copy`, an all-zero value may not correspond to any legitimate
 229     /// state for the type in question.
 230     pub fn init<T>() -> T;
 231
 232     /// Creates an uninitialized value.
 233     ///
 234     /// `uninit` is unsafe because there is no guarantee of what its
 235     /// contents are. In particular its drop-flag may be set to any
 236     /// state, which means it may claim either dropped or
 237     /// undropped. In the general case one must use `ptr::write` to
 238     /// initialize memory previous set to the result of `uninit`.
 239     pub fn uninit<T>() -> T;
 240
 241     /// Moves a value out of scope without running drop glue.
 242     pub fn forget<T>(_: T) -> ();
 243
 244     /// Unsafely transforms a value of one type into a value of another type.
 245     ///
 246     /// Both types must have the same size.
 247     ///
 248     /// # Examples
 249     ///
 250     /// ```
 251     /// use std::mem;
 252     ///
 253     /// let v: &[u8] = unsafe { mem::transmute("L") };
 254     /// assert!(v == [76]);
 255     /// ```
 256     #[stable(feature = "rust1", since = "1.0.0")]
 257     pub fn transmute<T,U>(e: T) -> U;
 258
 259     /// Gives the address for the return value of the enclosing function.
 260     ///
 261     /// Using this intrinsic in a function that does not use an out pointer
 262     /// will trigger a compiler error.
 263     pub fn return_address() -> *const u8;
 264
 265     /// Returns `true` if the actual type given as `T` requires drop
 266     /// glue; returns `false` if the actual type provided for `T`
 267     /// implements `Copy`.
 268     ///
 269     /// If the actual type neither requires drop glue nor implements
 270     /// `Copy`, then may return `true` or `false`.
 271     pub fn needs_drop<T>() -> bool;
 272
 273     /// Calculates the offset from a pointer.
 274     ///
 275     /// This is implemented as an intrinsic to avoid converting to and from an
 276     /// integer, since the conversion would throw away aliasing information.
 277     ///
 278     /// # Safety
 279     ///
 280     /// Both the starting and resulting pointer must be either in bounds or one
 281     /// byte past the end of an allocated object. If either pointer is out of
 282     /// bounds or arithmetic overflow occurs then any further use of the
 283     /// returned value will result in undefined behavior.
 284     pub fn offset<T>(dst: *const T, offset: isize) -> *const T;
 285
 286     /// Copies `count * size_of<T>` bytes from `src` to `dst`. The source
 287     /// and destination may *not* overlap.
 288     ///
 289     /// `copy_nonoverlapping` is semantically equivalent to C's `memcpy`.
 290     ///
 291     /// # Safety
 292     ///
 293     /// Beyond requiring that the program must be allowed to access both regions
 294     /// of memory, it is Undefined Behaviour for source and destination to
 295     /// overlap. Care must also be taken with the ownership of `src` and
 296     /// `dst`. This method semantically moves the values of `src` into `dst`.
 297     /// However it does not drop the contents of `dst`, or prevent the contents
 298     /// of `src` from being dropped or used.
 299     ///
 300     /// # Examples
 301     ///
 302     /// A safe swap function:
 303     ///
 304     /// ```
 305     /// # #![feature(core)]
 306     /// use std::mem;
 307     /// use std::ptr;
 308     ///
 309     /// fn swap<T>(x: &mut T, y: &mut T) {
 310     ///     unsafe {
 311     ///         // Give ourselves some scratch space to work with
 312     ///         let mut t: T = mem::uninitialized();
 313     ///
 314     ///         // Perform the swap, `&mut` pointers never alias
 315     ///         ptr::copy_nonoverlapping(x, &mut t, 1);
 316     ///         ptr::copy_nonoverlapping(y, x, 1);
 317     ///         ptr::copy_nonoverlapping(&t, y, 1);
 318     ///
 319     ///         // y and t now point to the same thing, but we need to completely forget `tmp`
 320     ///         // because it's no longer relevant.
 321     ///         mem::forget(t);
 322     ///     }
 323     /// }
 324     /// ```
 325     #[stable(feature = "rust1", since = "1.0.0")]
 326     pub fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
 327
 328     /// Copies `count * size_of<T>` bytes from `src` to `dst`. The source
 329     /// and destination may overlap.
 330     ///
 331     /// `copy` is semantically equivalent to C's `memmove`.
 332     ///
 333     /// # Safety
 334     ///
 335     /// Care must be taken with the ownership of `src` and `dst`.
 336     /// This method semantically moves the values of `src` into `dst`.
 337     /// However it does not drop the contents of `dst`, or prevent the contents of `src`
 338     /// from being dropped or used.
 339     ///
 340     /// # Examples
 341     ///
 342     /// Efficiently create a Rust vector from an unsafe buffer:
 343     ///
 344     /// ```
 345     /// # #![feature(core)]
 346     /// use std::ptr;
 347     ///
 348     /// unsafe fn from_buf_raw<T>(ptr: *const T, elts: usize) -> Vec<T> {
 349     ///     let mut dst = Vec::with_capacity(elts);
 350     ///     dst.set_len(elts);
 351     ///     ptr::copy(ptr, dst.as_mut_ptr(), elts);
 352     ///     dst
 353     /// }
 354     /// ```
 355     ///
 356     #[stable(feature = "rust1", since = "1.0.0")]
 357     pub fn copy<T>(src: *const T, dst: *mut T, count: usize);
 358
 359     /// Invokes memset on the specified pointer, setting `count * size_of::<T>()`
 360     /// bytes of memory starting at `dst` to `c`.
 361     #[stable(feature = "rust1", since = "1.0.0")]
 362     pub fn write_bytes<T>(dst: *mut T, val: u8, count: usize);
 363
 364     /// Equivalent to the appropriate `llvm.memcpy.p0i8.0i8.*` intrinsic, with
 365     /// a size of `count` * `size_of::<T>()` and an alignment of
 366     /// `min_align_of::<T>()`
 367     ///
 368     /// The volatile parameter parameter is set to `true`, so it will not be optimized out.
 369     pub fn volatile_copy_nonoverlapping_memory<T>(dst: *mut T, src: *const T,
 370                                                   count: usize);
 371     /// Equivalent to the appropriate `llvm.memmove.p0i8.0i8.*` intrinsic, with
 372     /// a size of `count` * `size_of::<T>()` and an alignment of
 373     /// `min_align_of::<T>()`
 374     ///
 375     /// The volatile parameter parameter is set to `true`, so it will not be optimized out.
 376     pub fn volatile_copy_memory<T>(dst: *mut T, src: *const T, count: usize);
 377     /// Equivalent to the appropriate `llvm.memset.p0i8.*` intrinsic, with a
 378     /// size of `count` * `size_of::<T>()` and an alignment of
 379     /// `min_align_of::<T>()`.
 380     ///
 381     /// The volatile parameter parameter is set to `true`, so it will not be optimized out.
 382     pub fn volatile_set_memory<T>(dst: *mut T, val: u8, count: usize);
 383
 384     /// Perform a volatile load from the `src` pointer.
 385     pub fn volatile_load<T>(src: *const T) -> T;
 386     /// Perform a volatile store to the `dst` pointer.
 387     pub fn volatile_store<T>(dst: *mut T, val: T);
 388
 389     /// Returns the square root of an `f32`
 390     pub fn sqrtf32(x: f32) -> f32;
 391     /// Returns the square root of an `f64`
 392     pub fn sqrtf64(x: f64) -> f64;
 393
 394     /// Raises an `f32` to an integer power.
 395     pub fn powif32(a: f32, x: i32) -> f32;
 396     /// Raises an `f64` to an integer power.
 397     pub fn powif64(a: f64, x: i32) -> f64;
 398
 399     /// Returns the sine of an `f32`.
 400     pub fn sinf32(x: f32) -> f32;
 401     /// Returns the sine of an `f64`.
 402     pub fn sinf64(x: f64) -> f64;
 403
 404     /// Returns the cosine of an `f32`.
 405     pub fn cosf32(x: f32) -> f32;
 406     /// Returns the cosine of an `f64`.
 407     pub fn cosf64(x: f64) -> f64;
 408
 409     /// Raises an `f32` to an `f32` power.
 410     pub fn powf32(a: f32, x: f32) -> f32;
 411     /// Raises an `f64` to an `f64` power.
 412     pub fn powf64(a: f64, x: f64) -> f64;
 413
 414     /// Returns the exponential of an `f32`.
 415     pub fn expf32(x: f32) -> f32;
 416     /// Returns the exponential of an `f64`.
 417     pub fn expf64(x: f64) -> f64;
 418
 419     /// Returns 2 raised to the power of an `f32`.
 420     pub fn exp2f32(x: f32) -> f32;
 421     /// Returns 2 raised to the power of an `f64`.
 422     pub fn exp2f64(x: f64) -> f64;
 423
 424     /// Returns the natural logarithm of an `f32`.
 425     pub fn logf32(x: f32) -> f32;
 426     /// Returns the natural logarithm of an `f64`.
 427     pub fn logf64(x: f64) -> f64;
 428
 429     /// Returns the base 10 logarithm of an `f32`.
 430     pub fn log10f32(x: f32) -> f32;
 431     /// Returns the base 10 logarithm of an `f64`.
 432     pub fn log10f64(x: f64) -> f64;
 433
 434     /// Returns the base 2 logarithm of an `f32`.
 435     pub fn log2f32(x: f32) -> f32;
 436     /// Returns the base 2 logarithm of an `f64`.
 437     pub fn log2f64(x: f64) -> f64;
 438
 439     /// Returns `a * b + c` for `f32` values.
 440     pub fn fmaf32(a: f32, b: f32, c: f32) -> f32;
 441     /// Returns `a * b + c` for `f64` values.
 442     pub fn fmaf64(a: f64, b: f64, c: f64) -> f64;
 443
 444     /// Returns the absolute value of an `f32`.
 445     pub fn fabsf32(x: f32) -> f32;
 446     /// Returns the absolute value of an `f64`.
 447     pub fn fabsf64(x: f64) -> f64;
 448
 449     /// Copies the sign from `y` to `x` for `f32` values.
 450     pub fn copysignf32(x: f32, y: f32) -> f32;
 451     /// Copies the sign from `y` to `x` for `f64` values.
 452     pub fn copysignf64(x: f64, y: f64) -> f64;
 453
 454     /// Returns the largest integer less than or equal to an `f32`.
 455     pub fn floorf32(x: f32) -> f32;
 456     /// Returns the largest integer less than or equal to an `f64`.
 457     pub fn floorf64(x: f64) -> f64;
 458
 459     /// Returns the smallest integer greater than or equal to an `f32`.
 460     pub fn ceilf32(x: f32) -> f32;
 461     /// Returns the smallest integer greater than or equal to an `f64`.
 462     pub fn ceilf64(x: f64) -> f64;
 463
 464     /// Returns the integer part of an `f32`.
 465     pub fn truncf32(x: f32) -> f32;
 466     /// Returns the integer part of an `f64`.
 467     pub fn truncf64(x: f64) -> f64;
 468
 469     /// Returns the nearest integer to an `f32`. May raise an inexact floating-point exception
 470     /// if the argument is not an integer.
 471     pub fn rintf32(x: f32) -> f32;
 472     /// Returns the nearest integer to an `f64`. May raise an inexact floating-point exception
 473     /// if the argument is not an integer.
 474     pub fn rintf64(x: f64) -> f64;
 475
 476     /// Returns the nearest integer to an `f32`.
 477     pub fn nearbyintf32(x: f32) -> f32;
 478     /// Returns the nearest integer to an `f64`.
 479     pub fn nearbyintf64(x: f64) -> f64;
 480
 481     /// Returns the nearest integer to an `f32`. Rounds half-way cases away from zero.
 482     pub fn roundf32(x: f32) -> f32;
 483     /// Returns the nearest integer to an `f64`. Rounds half-way cases away from zero.
 484     pub fn roundf64(x: f64) -> f64;
 485
 486     /// Returns the number of bits set in a `u8`.
 487     pub fn ctpop8(x: u8) -> u8;
 488     /// Returns the number of bits set in a `u16`.
 489     pub fn ctpop16(x: u16) -> u16;
 490     /// Returns the number of bits set in a `u32`.
 491     pub fn ctpop32(x: u32) -> u32;
 492     /// Returns the number of bits set in a `u64`.
 493     pub fn ctpop64(x: u64) -> u64;
 494
 495     /// Returns the number of leading bits unset in a `u8`.
 496     pub fn ctlz8(x: u8) -> u8;
 497     /// Returns the number of leading bits unset in a `u16`.
 498     pub fn ctlz16(x: u16) -> u16;
 499     /// Returns the number of leading bits unset in a `u32`.
 500     pub fn ctlz32(x: u32) -> u32;
 501     /// Returns the number of leading bits unset in a `u64`.
 502     pub fn ctlz64(x: u64) -> u64;
 503
 504     /// Returns the number of trailing bits unset in a `u8`.
 505     pub fn cttz8(x: u8) -> u8;
 506     /// Returns the number of trailing bits unset in a `u16`.
 507     pub fn cttz16(x: u16) -> u16;
 508     /// Returns the number of trailing bits unset in a `u32`.
 509     pub fn cttz32(x: u32) -> u32;
 510     /// Returns the number of trailing bits unset in a `u64`.
 511     pub fn cttz64(x: u64) -> u64;
 512
 513     /// Reverses the bytes in a `u16`.
 514     pub fn bswap16(x: u16) -> u16;
 515     /// Reverses the bytes in a `u32`.
 516     pub fn bswap32(x: u32) -> u32;
 517     /// Reverses the bytes in a `u64`.
 518     pub fn bswap64(x: u64) -> u64;
 519
 520     /// Performs checked `i8` addition.
 521     pub fn i8_add_with_overflow(x: i8, y: i8) -> (i8, bool);
 522     /// Performs checked `i16` addition.
 523     pub fn i16_add_with_overflow(x: i16, y: i16) -> (i16, bool);
 524     /// Performs checked `i32` addition.
 525     pub fn i32_add_with_overflow(x: i32, y: i32) -> (i32, bool);
 526     /// Performs checked `i64` addition.
 527     pub fn i64_add_with_overflow(x: i64, y: i64) -> (i64, bool);
 528
 529     /// Performs checked `u8` addition.
 530     pub fn u8_add_with_overflow(x: u8, y: u8) -> (u8, bool);
 531     /// Performs checked `u16` addition.
 532     pub fn u16_add_with_overflow(x: u16, y: u16) -> (u16, bool);
 533     /// Performs checked `u32` addition.
 534     pub fn u32_add_with_overflow(x: u32, y: u32) -> (u32, bool);
 535     /// Performs checked `u64` addition.
 536     pub fn u64_add_with_overflow(x: u64, y: u64) -> (u64, bool);
 537
 538     /// Performs checked `i8` subtraction.
 539     pub fn i8_sub_with_overflow(x: i8, y: i8) -> (i8, bool);
 540     /// Performs checked `i16` subtraction.
 541     pub fn i16_sub_with_overflow(x: i16, y: i16) -> (i16, bool);
 542     /// Performs checked `i32` subtraction.
 543     pub fn i32_sub_with_overflow(x: i32, y: i32) -> (i32, bool);
 544     /// Performs checked `i64` subtraction.
 545     pub fn i64_sub_with_overflow(x: i64, y: i64) -> (i64, bool);
 546
 547     /// Performs checked `u8` subtraction.
 548     pub fn u8_sub_with_overflow(x: u8, y: u8) -> (u8, bool);
 549     /// Performs checked `u16` subtraction.
 550     pub fn u16_sub_with_overflow(x: u16, y: u16) -> (u16, bool);
 551     /// Performs checked `u32` subtraction.
 552     pub fn u32_sub_with_overflow(x: u32, y: u32) -> (u32, bool);
 553     /// Performs checked `u64` subtraction.
 554     pub fn u64_sub_with_overflow(x: u64, y: u64) -> (u64, bool);
 555
 556     /// Performs checked `i8` multiplication.
 557     pub fn i8_mul_with_overflow(x: i8, y: i8) -> (i8, bool);
 558     /// Performs checked `i16` multiplication.
 559     pub fn i16_mul_with_overflow(x: i16, y: i16) -> (i16, bool);
 560     /// Performs checked `i32` multiplication.
 561     pub fn i32_mul_with_overflow(x: i32, y: i32) -> (i32, bool);
 562     /// Performs checked `i64` multiplication.
 563     pub fn i64_mul_with_overflow(x: i64, y: i64) -> (i64, bool);
 564
 565     /// Performs checked `u8` multiplication.
 566     pub fn u8_mul_with_overflow(x: u8, y: u8) -> (u8, bool);
 567     /// Performs checked `u16` multiplication.
 568     pub fn u16_mul_with_overflow(x: u16, y: u16) -> (u16, bool);
 569     /// Performs checked `u32` multiplication.
 570     pub fn u32_mul_with_overflow(x: u32, y: u32) -> (u32, bool);
 571     /// Performs checked `u64` multiplication.
 572     pub fn u64_mul_with_overflow(x: u64, y: u64) -> (u64, bool);
 573
 574     /// Returns (a + b) mod 2^N, where N is the width of N in bits.
 575     pub fn overflowing_add<T>(a: T, b: T) -> T;
 576     /// Returns (a - b) mod 2^N, where N is the width of N in bits.
 577     pub fn overflowing_sub<T>(a: T, b: T) -> T;
 578     /// Returns (a * b) mod 2^N, where N is the width of N in bits.
 579     pub fn overflowing_mul<T>(a: T, b: T) -> T;
 580
 581     /// Returns the value of the discriminant for the variant in 'v',
 582     /// cast to a `u64`; if `T` has no discriminant, returns 0.
 583     pub fn discriminant_value<T>(v: &T) -> u64;
 584 }
 585
 586 #[cfg(not(stage0))]
 587 extern "rust-intrinsic" {
 588     /// Performs an unchecked signed division, which results in undefined behavior,
 589     /// in cases where y == 0, or x == int::MIN and y == -1
 590     pub fn unchecked_sdiv<T>(x: T, y: T) -> T;
 591     /// Performs an unchecked unsigned division, which results in undefined behavior,
 592     /// in cases where y == 0
 593     pub fn unchecked_udiv<T>(x: T, y: T) -> T;
 594
 595     /// Returns the remainder of an unchecked signed division, which results in
 596     /// undefined behavior, in cases where y == 0, or x == int::MIN and y == -1
 597     pub fn unchecked_urem<T>(x: T, y: T) -> T;
 598     /// Returns the remainder of an unchecked signed division, which results in
 599     /// undefined behavior, in cases where y == 0
 600     pub fn unchecked_srem<T>(x: T, y: T) -> T;
 601 }