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_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 #![allow(missing_docs)]
  47
  48 use marker::Sized;
  49
  50 extern "rust-intrinsic" {
  51
  52     // NB: These intrinsics take raw pointers because they mutate aliased
  53     // memory, which is not valid for either `&` or `&mut`.
  54
  55     pub fn atomic_cxchg<T>(dst: *mut T, old: T, src: T) -> T;
  56     pub fn atomic_cxchg_acq<T>(dst: *mut T, old: T, src: T) -> T;
  57     pub fn atomic_cxchg_rel<T>(dst: *mut T, old: T, src: T) -> T;
  58     pub fn atomic_cxchg_acqrel<T>(dst: *mut T, old: T, src: T) -> T;
  59     pub fn atomic_cxchg_relaxed<T>(dst: *mut T, old: T, src: T) -> T;
  60
  61     pub fn atomic_load<T>(src: *const T) -> T;
  62     pub fn atomic_load_acq<T>(src: *const T) -> T;
  63     pub fn atomic_load_relaxed<T>(src: *const T) -> T;
  64     pub fn atomic_load_unordered<T>(src: *const T) -> T;
  65
  66     pub fn atomic_store<T>(dst: *mut T, val: T);
  67     pub fn atomic_store_rel<T>(dst: *mut T, val: T);
  68     pub fn atomic_store_relaxed<T>(dst: *mut T, val: T);
  69     pub fn atomic_store_unordered<T>(dst: *mut T, val: T);
  70
  71     pub fn atomic_xchg<T>(dst: *mut T, src: T) -> T;
  72     pub fn atomic_xchg_acq<T>(dst: *mut T, src: T) -> T;
  73     pub fn atomic_xchg_rel<T>(dst: *mut T, src: T) -> T;
  74     pub fn atomic_xchg_acqrel<T>(dst: *mut T, src: T) -> T;
  75     pub fn atomic_xchg_relaxed<T>(dst: *mut T, src: T) -> T;
  76
  77     pub fn atomic_xadd<T>(dst: *mut T, src: T) -> T;
  78     pub fn atomic_xadd_acq<T>(dst: *mut T, src: T) -> T;
  79     pub fn atomic_xadd_rel<T>(dst: *mut T, src: T) -> T;
  80     pub fn atomic_xadd_acqrel<T>(dst: *mut T, src: T) -> T;
  81     pub fn atomic_xadd_relaxed<T>(dst: *mut T, src: T) -> T;
  82
  83     pub fn atomic_xsub<T>(dst: *mut T, src: T) -> T;
  84     pub fn atomic_xsub_acq<T>(dst: *mut T, src: T) -> T;
  85     pub fn atomic_xsub_rel<T>(dst: *mut T, src: T) -> T;
  86     pub fn atomic_xsub_acqrel<T>(dst: *mut T, src: T) -> T;
  87     pub fn atomic_xsub_relaxed<T>(dst: *mut T, src: T) -> T;
  88
  89     pub fn atomic_and<T>(dst: *mut T, src: T) -> T;
  90     pub fn atomic_and_acq<T>(dst: *mut T, src: T) -> T;
  91     pub fn atomic_and_rel<T>(dst: *mut T, src: T) -> T;
  92     pub fn atomic_and_acqrel<T>(dst: *mut T, src: T) -> T;
  93     pub fn atomic_and_relaxed<T>(dst: *mut T, src: T) -> T;
  94
  95     pub fn atomic_nand<T>(dst: *mut T, src: T) -> T;
  96     pub fn atomic_nand_acq<T>(dst: *mut T, src: T) -> T;
  97     pub fn atomic_nand_rel<T>(dst: *mut T, src: T) -> T;
  98     pub fn atomic_nand_acqrel<T>(dst: *mut T, src: T) -> T;
  99     pub fn atomic_nand_relaxed<T>(dst: *mut T, src: T) -> T;
 100
 101     pub fn atomic_or<T>(dst: *mut T, src: T) -> T;
 102     pub fn atomic_or_acq<T>(dst: *mut T, src: T) -> T;
 103     pub fn atomic_or_rel<T>(dst: *mut T, src: T) -> T;
 104     pub fn atomic_or_acqrel<T>(dst: *mut T, src: T) -> T;
 105     pub fn atomic_or_relaxed<T>(dst: *mut T, src: T) -> T;
 106
 107     pub fn atomic_xor<T>(dst: *mut T, src: T) -> T;
 108     pub fn atomic_xor_acq<T>(dst: *mut T, src: T) -> T;
 109     pub fn atomic_xor_rel<T>(dst: *mut T, src: T) -> T;
 110     pub fn atomic_xor_acqrel<T>(dst: *mut T, src: T) -> T;
 111     pub fn atomic_xor_relaxed<T>(dst: *mut T, src: T) -> T;
 112
 113     pub fn atomic_max<T>(dst: *mut T, src: T) -> T;
 114     pub fn atomic_max_acq<T>(dst: *mut T, src: T) -> T;
 115     pub fn atomic_max_rel<T>(dst: *mut T, src: T) -> T;
 116     pub fn atomic_max_acqrel<T>(dst: *mut T, src: T) -> T;
 117     pub fn atomic_max_relaxed<T>(dst: *mut T, src: T) -> T;
 118
 119     pub fn atomic_min<T>(dst: *mut T, src: T) -> T;
 120     pub fn atomic_min_acq<T>(dst: *mut T, src: T) -> T;
 121     pub fn atomic_min_rel<T>(dst: *mut T, src: T) -> T;
 122     pub fn atomic_min_acqrel<T>(dst: *mut T, src: T) -> T;
 123     pub fn atomic_min_relaxed<T>(dst: *mut T, src: T) -> T;
 124
 125     pub fn atomic_umin<T>(dst: *mut T, src: T) -> T;
 126     pub fn atomic_umin_acq<T>(dst: *mut T, src: T) -> T;
 127     pub fn atomic_umin_rel<T>(dst: *mut T, src: T) -> T;
 128     pub fn atomic_umin_acqrel<T>(dst: *mut T, src: T) -> T;
 129     pub fn atomic_umin_relaxed<T>(dst: *mut T, src: T) -> T;
 130
 131     pub fn atomic_umax<T>(dst: *mut T, src: T) -> T;
 132     pub fn atomic_umax_acq<T>(dst: *mut T, src: T) -> T;
 133     pub fn atomic_umax_rel<T>(dst: *mut T, src: T) -> T;
 134     pub fn atomic_umax_acqrel<T>(dst: *mut T, src: T) -> T;
 135     pub fn atomic_umax_relaxed<T>(dst: *mut T, src: T) -> T;
 136 }
 137
 138 extern "rust-intrinsic" {
 139
 140     pub fn atomic_fence();
 141     pub fn atomic_fence_acq();
 142     pub fn atomic_fence_rel();
 143     pub fn atomic_fence_acqrel();
 144
 145     /// A compiler-only memory barrier.
 146     ///
 147     /// Memory accesses will never be reordered across this barrier by the
 148     /// compiler, but no instructions will be emitted for it. This is
 149     /// appropriate for operations on the same thread that may be preempted,
 150     /// such as when interacting with signal handlers.
 151     pub fn atomic_singlethreadfence();
 152     pub fn atomic_singlethreadfence_acq();
 153     pub fn atomic_singlethreadfence_rel();
 154     pub fn atomic_singlethreadfence_acqrel();
 155
 156     /// Aborts the execution of the process.
 157     pub fn abort() -> !;
 158
 159     /// Tells LLVM that this point in the code is not reachable,
 160     /// enabling further optimizations.
 161     ///
 162     /// NB: This is very different from the `unreachable!()` macro!
 163     pub fn unreachable() -> !;
 164
 165     /// Informs the optimizer that a condition is always true.
 166     /// If the condition is false, the behavior is undefined.
 167     ///
 168     /// No code is generated for this intrinsic, but the optimizer will try
 169     /// to preserve it (and its condition) between passes, which may interfere
 170     /// with optimization of surrounding code and reduce performance. It should
 171     /// not be used if the invariant can be discovered by the optimizer on its
 172     /// own, or if it does not enable any significant optimizations.
 173     pub fn assume(b: bool);
 174
 175     /// Executes a breakpoint trap, for inspection by a debugger.
 176     pub fn breakpoint();
 177
 178     /// The size of a type in bytes.
 179     ///
 180     /// This is the exact number of bytes in memory taken up by a
 181     /// value of the given type. In other words, a memset of this size
 182     /// would *exactly* overwrite a value. When laid out in vectors
 183     /// and structures there may be additional padding between
 184     /// elements.
 185     pub fn size_of<T>() -> usize;
 186
 187     /// Moves a value to an uninitialized memory location.
 188     ///
 189     /// Drop glue is not run on the destination.
 190     pub fn move_val_init<T>(dst: *mut T, src: T);
 191
 192     pub fn min_align_of<T>() -> usize;
 193     pub fn pref_align_of<T>() -> usize;
 194
 195     pub fn size_of_val<T: ?Sized>(_: &T) -> usize;
 196     pub fn min_align_of_val<T: ?Sized>(_: &T) -> usize;
 197     pub fn drop_in_place<T: ?Sized>(_: *mut T);
 198
 199     /// Gets a static string slice containing the name of a type.
 200     pub fn type_name<T: ?Sized>() -> &'static str;
 201
 202     /// Gets an identifier which is globally unique to the specified type. This
 203     /// function will return the same value for a type regardless of whichever
 204     /// crate it is invoked in.
 205     pub fn type_id<T: ?Sized + 'static>() -> u64;
 206
 207     /// Creates a value initialized to so that its drop flag,
 208     /// if any, says that it has been dropped.
 209     ///
 210     /// `init_dropped` is unsafe because it returns a datum with all
 211     /// of its bytes set to the drop flag, which generally does not
 212     /// correspond to a valid value.
 213     ///
 214     /// This intrinsic is likely to be deprecated in the future when
 215     /// Rust moves to non-zeroing dynamic drop (and thus removes the
 216     /// embedded drop flags that are being established by this
 217     /// intrinsic).
 218     pub fn init_dropped<T>() -> T;
 219
 220     /// Creates a value initialized to zero.
 221     ///
 222     /// `init` is unsafe because it returns a zeroed-out datum,
 223     /// which is unsafe unless T is `Copy`.  Also, even if T is
 224     /// `Copy`, an all-zero value may not correspond to any legitimate
 225     /// state for the type in question.
 226     pub fn init<T>() -> T;
 227
 228     /// Creates an uninitialized value.
 229     ///
 230     /// `uninit` is unsafe because there is no guarantee of what its
 231     /// contents are. In particular its drop-flag may be set to any
 232     /// state, which means it may claim either dropped or
 233     /// undropped. In the general case one must use `ptr::write` to
 234     /// initialize memory previous set to the result of `uninit`.
 235     pub fn uninit<T>() -> T;
 236
 237     /// Moves a value out of scope without running drop glue.
 238     pub fn forget<T>(_: T) -> ();
 239
 240     /// Unsafely transforms a value of one type into a value of another type.
 241     ///
 242     /// Both types must have the same size.
 243     ///
 244     /// # Examples
 245     ///
 246     /// ```
 247     /// use std::mem;
 248     ///
 249     /// let v: &[u8] = unsafe { mem::transmute("L") };
 250     /// assert!(v == [76]);
 251     /// ```
 252     #[stable(feature = "rust1", since = "1.0.0")]
 253     pub fn transmute<T,U>(e: T) -> U;
 254
 255     /// Gives the address for the return value of the enclosing function.
 256     ///
 257     /// Using this intrinsic in a function that does not use an out pointer
 258     /// will trigger a compiler error.
 259     pub fn return_address() -> *const u8;
 260
 261     /// Returns `true` if the actual type given as `T` requires drop
 262     /// glue; returns `false` if the actual type provided for `T`
 263     /// implements `Copy`.
 264     ///
 265     /// If the actual type neither requires drop glue nor implements
 266     /// `Copy`, then may return `true` or `false`.
 267     pub fn needs_drop<T>() -> bool;
 268
 269     /// Calculates the offset from a pointer.
 270     ///
 271     /// This is implemented as an intrinsic to avoid converting to and from an
 272     /// integer, since the conversion would throw away aliasing information.
 273     ///
 274     /// # Safety
 275     ///
 276     /// Both the starting and resulting pointer must be either in bounds or one
 277     /// byte past the end of an allocated object. If either pointer is out of
 278     /// bounds or arithmetic overflow occurs then any further use of the
 279     /// returned value will result in undefined behavior.
 280     pub fn offset<T>(dst: *const T, offset: isize) -> *const T;
 281
 282     /// Calculates the offset from a pointer, potentially wrapping.
 283     ///
 284     /// This is implemented as an intrinsic to avoid converting to and from an
 285     /// integer, since the conversion inhibits certain optimizations.
 286     ///
 287     /// # Safety
 288     ///
 289     /// Unlike the `offset` intrinsic, this intrinsic does not restrict the
 290     /// resulting pointer to point into or one byte past the end of an allocated
 291     /// object, and it wraps with two's complement arithmetic. The resulting
 292     /// value is not necessarily valid to be used to actually access memory.
 293     pub fn arith_offset<T>(dst: *const T, offset: isize) -> *const T;
 294
 295     /// Copies `count * size_of<T>` bytes from `src` to `dst`. The source
 296     /// and destination may *not* overlap.
 297     ///
 298     /// `copy_nonoverlapping` is semantically equivalent to C's `memcpy`.
 299     ///
 300     /// # Safety
 301     ///
 302     /// Beyond requiring that the program must be allowed to access both regions
 303     /// of memory, it is Undefined Behaviour for source and destination to
 304     /// overlap. Care must also be taken with the ownership of `src` and
 305     /// `dst`. This method semantically moves the values of `src` into `dst`.
 306     /// However it does not drop the contents of `dst`, or prevent the contents
 307     /// of `src` from being dropped or used.
 308     ///
 309     /// # Examples
 310     ///
 311     /// A safe swap function:
 312     ///
 313     /// ```
 314     /// use std::mem;
 315     /// use std::ptr;
 316     ///
 317     /// fn swap<T>(x: &mut T, y: &mut T) {
 318     ///     unsafe {
 319     ///         // Give ourselves some scratch space to work with
 320     ///         let mut t: T = mem::uninitialized();
 321     ///
 322     ///         // Perform the swap, `&mut` pointers never alias
 323     ///         ptr::copy_nonoverlapping(x, &mut t, 1);
 324     ///         ptr::copy_nonoverlapping(y, x, 1);
 325     ///         ptr::copy_nonoverlapping(&t, y, 1);
 326     ///
 327     ///         // y and t now point to the same thing, but we need to completely forget `tmp`
 328     ///         // because it's no longer relevant.
 329     ///         mem::forget(t);
 330     ///     }
 331     /// }
 332     /// ```
 333     #[stable(feature = "rust1", since = "1.0.0")]
 334     pub fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
 335
 336     /// Copies `count * size_of<T>` bytes from `src` to `dst`. The source
 337     /// and destination may overlap.
 338     ///
 339     /// `copy` is semantically equivalent to C's `memmove`.
 340     ///
 341     /// # Safety
 342     ///
 343     /// Care must be taken with the ownership of `src` and `dst`.
 344     /// This method semantically moves the values of `src` into `dst`.
 345     /// However it does not drop the contents of `dst`, or prevent the contents of `src`
 346     /// from being dropped or used.
 347     ///
 348     /// # Examples
 349     ///
 350     /// Efficiently create a Rust vector from an unsafe buffer:
 351     ///
 352     /// ```
 353     /// use std::ptr;
 354     ///
 355     /// unsafe fn from_buf_raw<T>(ptr: *const T, elts: usize) -> Vec<T> {
 356     ///     let mut dst = Vec::with_capacity(elts);
 357     ///     dst.set_len(elts);
 358     ///     ptr::copy(ptr, dst.as_mut_ptr(), elts);
 359     ///     dst
 360     /// }
 361     /// ```
 362     ///
 363     #[stable(feature = "rust1", since = "1.0.0")]
 364     pub fn copy<T>(src: *const T, dst: *mut T, count: usize);
 365
 366     /// Invokes memset on the specified pointer, setting `count * size_of::<T>()`
 367     /// bytes of memory starting at `dst` to `c`.
 368     #[stable(feature = "rust1", since = "1.0.0")]
 369     pub fn write_bytes<T>(dst: *mut T, val: u8, count: usize);
 370
 371     /// Equivalent to the appropriate `llvm.memcpy.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_nonoverlapping_memory<T>(dst: *mut T, src: *const T,
 377                                                   count: usize);
 378     /// Equivalent to the appropriate `llvm.memmove.p0i8.0i8.*` intrinsic, with
 379     /// a size of `count` * `size_of::<T>()` and an alignment of
 380     /// `min_align_of::<T>()`
 381     ///
 382     /// The volatile parameter parameter is set to `true`, so it will not be optimized out.
 383     pub fn volatile_copy_memory<T>(dst: *mut T, src: *const T, count: usize);
 384     /// Equivalent to the appropriate `llvm.memset.p0i8.*` intrinsic, with a
 385     /// size of `count` * `size_of::<T>()` and an alignment of
 386     /// `min_align_of::<T>()`.
 387     ///
 388     /// The volatile parameter parameter is set to `true`, so it will not be optimized out.
 389     pub fn volatile_set_memory<T>(dst: *mut T, val: u8, count: usize);
 390
 391     /// Perform a volatile load from the `src` pointer.
 392     pub fn volatile_load<T>(src: *const T) -> T;
 393     /// Perform a volatile store to the `dst` pointer.
 394     pub fn volatile_store<T>(dst: *mut T, val: T);
 395
 396     /// Returns the square root of an `f32`
 397     pub fn sqrtf32(x: f32) -> f32;
 398     /// Returns the square root of an `f64`
 399     pub fn sqrtf64(x: f64) -> f64;
 400
 401     /// Raises an `f32` to an integer power.
 402     pub fn powif32(a: f32, x: i32) -> f32;
 403     /// Raises an `f64` to an integer power.
 404     pub fn powif64(a: f64, x: i32) -> f64;
 405
 406     /// Returns the sine of an `f32`.
 407     pub fn sinf32(x: f32) -> f32;
 408     /// Returns the sine of an `f64`.
 409     pub fn sinf64(x: f64) -> f64;
 410
 411     /// Returns the cosine of an `f32`.
 412     pub fn cosf32(x: f32) -> f32;
 413     /// Returns the cosine of an `f64`.
 414     pub fn cosf64(x: f64) -> f64;
 415
 416     /// Raises an `f32` to an `f32` power.
 417     pub fn powf32(a: f32, x: f32) -> f32;
 418     /// Raises an `f64` to an `f64` power.
 419     pub fn powf64(a: f64, x: f64) -> f64;
 420
 421     /// Returns the exponential of an `f32`.
 422     pub fn expf32(x: f32) -> f32;
 423     /// Returns the exponential of an `f64`.
 424     pub fn expf64(x: f64) -> f64;
 425
 426     /// Returns 2 raised to the power of an `f32`.
 427     pub fn exp2f32(x: f32) -> f32;
 428     /// Returns 2 raised to the power of an `f64`.
 429     pub fn exp2f64(x: f64) -> f64;
 430
 431     /// Returns the natural logarithm of an `f32`.
 432     pub fn logf32(x: f32) -> f32;
 433     /// Returns the natural logarithm of an `f64`.
 434     pub fn logf64(x: f64) -> f64;
 435
 436     /// Returns the base 10 logarithm of an `f32`.
 437     pub fn log10f32(x: f32) -> f32;
 438     /// Returns the base 10 logarithm of an `f64`.
 439     pub fn log10f64(x: f64) -> f64;
 440
 441     /// Returns the base 2 logarithm of an `f32`.
 442     pub fn log2f32(x: f32) -> f32;
 443     /// Returns the base 2 logarithm of an `f64`.
 444     pub fn log2f64(x: f64) -> f64;
 445
 446     /// Returns `a * b + c` for `f32` values.
 447     pub fn fmaf32(a: f32, b: f32, c: f32) -> f32;
 448     /// Returns `a * b + c` for `f64` values.
 449     pub fn fmaf64(a: f64, b: f64, c: f64) -> f64;
 450
 451     /// Returns the absolute value of an `f32`.
 452     pub fn fabsf32(x: f32) -> f32;
 453     /// Returns the absolute value of an `f64`.
 454     pub fn fabsf64(x: f64) -> f64;
 455
 456     /// Copies the sign from `y` to `x` for `f32` values.
 457     pub fn copysignf32(x: f32, y: f32) -> f32;
 458     /// Copies the sign from `y` to `x` for `f64` values.
 459     pub fn copysignf64(x: f64, y: f64) -> f64;
 460
 461     /// Returns the largest integer less than or equal to an `f32`.
 462     pub fn floorf32(x: f32) -> f32;
 463     /// Returns the largest integer less than or equal to an `f64`.
 464     pub fn floorf64(x: f64) -> f64;
 465
 466     /// Returns the smallest integer greater than or equal to an `f32`.
 467     pub fn ceilf32(x: f32) -> f32;
 468     /// Returns the smallest integer greater than or equal to an `f64`.
 469     pub fn ceilf64(x: f64) -> f64;
 470
 471     /// Returns the integer part of an `f32`.
 472     pub fn truncf32(x: f32) -> f32;
 473     /// Returns the integer part of an `f64`.
 474     pub fn truncf64(x: f64) -> f64;
 475
 476     /// Returns the nearest integer to an `f32`. May raise an inexact floating-point exception
 477     /// if the argument is not an integer.
 478     pub fn rintf32(x: f32) -> f32;
 479     /// Returns the nearest integer to an `f64`. May raise an inexact floating-point exception
 480     /// if the argument is not an integer.
 481     pub fn rintf64(x: f64) -> f64;
 482
 483     /// Returns the nearest integer to an `f32`.
 484     pub fn nearbyintf32(x: f32) -> f32;
 485     /// Returns the nearest integer to an `f64`.
 486     pub fn nearbyintf64(x: f64) -> f64;
 487
 488     /// Returns the nearest integer to an `f32`. Rounds half-way cases away from zero.
 489     pub fn roundf32(x: f32) -> f32;
 490     /// Returns the nearest integer to an `f64`. Rounds half-way cases away from zero.
 491     pub fn roundf64(x: f64) -> f64;
 492
 493     /// Returns the number of bits set in a `u8`.
 494     pub fn ctpop8(x: u8) -> u8;
 495     /// Returns the number of bits set in a `u16`.
 496     pub fn ctpop16(x: u16) -> u16;
 497     /// Returns the number of bits set in a `u32`.
 498     pub fn ctpop32(x: u32) -> u32;
 499     /// Returns the number of bits set in a `u64`.
 500     pub fn ctpop64(x: u64) -> u64;
 501
 502     /// Returns the number of leading bits unset in a `u8`.
 503     pub fn ctlz8(x: u8) -> u8;
 504     /// Returns the number of leading bits unset in a `u16`.
 505     pub fn ctlz16(x: u16) -> u16;
 506     /// Returns the number of leading bits unset in a `u32`.
 507     pub fn ctlz32(x: u32) -> u32;
 508     /// Returns the number of leading bits unset in a `u64`.
 509     pub fn ctlz64(x: u64) -> u64;
 510
 511     /// Returns the number of trailing bits unset in a `u8`.
 512     pub fn cttz8(x: u8) -> u8;
 513     /// Returns the number of trailing bits unset in a `u16`.
 514     pub fn cttz16(x: u16) -> u16;
 515     /// Returns the number of trailing bits unset in a `u32`.
 516     pub fn cttz32(x: u32) -> u32;
 517     /// Returns the number of trailing bits unset in a `u64`.
 518     pub fn cttz64(x: u64) -> u64;
 519
 520     /// Reverses the bytes in a `u16`.
 521     pub fn bswap16(x: u16) -> u16;
 522     /// Reverses the bytes in a `u32`.
 523     pub fn bswap32(x: u32) -> u32;
 524     /// Reverses the bytes in a `u64`.
 525     pub fn bswap64(x: u64) -> u64;
 526
 527     /// Performs checked `i8` addition.
 528     pub fn i8_add_with_overflow(x: i8, y: i8) -> (i8, bool);
 529     /// Performs checked `i16` addition.
 530     pub fn i16_add_with_overflow(x: i16, y: i16) -> (i16, bool);
 531     /// Performs checked `i32` addition.
 532     pub fn i32_add_with_overflow(x: i32, y: i32) -> (i32, bool);
 533     /// Performs checked `i64` addition.
 534     pub fn i64_add_with_overflow(x: i64, y: i64) -> (i64, bool);
 535
 536     /// Performs checked `u8` addition.
 537     pub fn u8_add_with_overflow(x: u8, y: u8) -> (u8, bool);
 538     /// Performs checked `u16` addition.
 539     pub fn u16_add_with_overflow(x: u16, y: u16) -> (u16, bool);
 540     /// Performs checked `u32` addition.
 541     pub fn u32_add_with_overflow(x: u32, y: u32) -> (u32, bool);
 542     /// Performs checked `u64` addition.
 543     pub fn u64_add_with_overflow(x: u64, y: u64) -> (u64, bool);
 544
 545     /// Performs checked `i8` subtraction.
 546     pub fn i8_sub_with_overflow(x: i8, y: i8) -> (i8, bool);
 547     /// Performs checked `i16` subtraction.
 548     pub fn i16_sub_with_overflow(x: i16, y: i16) -> (i16, bool);
 549     /// Performs checked `i32` subtraction.
 550     pub fn i32_sub_with_overflow(x: i32, y: i32) -> (i32, bool);
 551     /// Performs checked `i64` subtraction.
 552     pub fn i64_sub_with_overflow(x: i64, y: i64) -> (i64, bool);
 553
 554     /// Performs checked `u8` subtraction.
 555     pub fn u8_sub_with_overflow(x: u8, y: u8) -> (u8, bool);
 556     /// Performs checked `u16` subtraction.
 557     pub fn u16_sub_with_overflow(x: u16, y: u16) -> (u16, bool);
 558     /// Performs checked `u32` subtraction.
 559     pub fn u32_sub_with_overflow(x: u32, y: u32) -> (u32, bool);
 560     /// Performs checked `u64` subtraction.
 561     pub fn u64_sub_with_overflow(x: u64, y: u64) -> (u64, bool);
 562
 563     /// Performs checked `i8` multiplication.
 564     pub fn i8_mul_with_overflow(x: i8, y: i8) -> (i8, bool);
 565     /// Performs checked `i16` multiplication.
 566     pub fn i16_mul_with_overflow(x: i16, y: i16) -> (i16, bool);
 567     /// Performs checked `i32` multiplication.
 568     pub fn i32_mul_with_overflow(x: i32, y: i32) -> (i32, bool);
 569     /// Performs checked `i64` multiplication.
 570     pub fn i64_mul_with_overflow(x: i64, y: i64) -> (i64, bool);
 571
 572     /// Performs checked `u8` multiplication.
 573     pub fn u8_mul_with_overflow(x: u8, y: u8) -> (u8, bool);
 574     /// Performs checked `u16` multiplication.
 575     pub fn u16_mul_with_overflow(x: u16, y: u16) -> (u16, bool);
 576     /// Performs checked `u32` multiplication.
 577     pub fn u32_mul_with_overflow(x: u32, y: u32) -> (u32, bool);
 578     /// Performs checked `u64` multiplication.
 579     pub fn u64_mul_with_overflow(x: u64, y: u64) -> (u64, bool);
 580
 581     /// Returns (a + b) mod 2^N, where N is the width of N in bits.
 582     pub fn overflowing_add<T>(a: T, b: T) -> T;
 583     /// Returns (a - b) mod 2^N, where N is the width of N in bits.
 584     pub fn overflowing_sub<T>(a: T, b: T) -> T;
 585     /// Returns (a * b) mod 2^N, where N is the width of N in bits.
 586     pub fn overflowing_mul<T>(a: T, b: T) -> T;
 587
 588     /// Performs an unchecked signed division, which results in undefined behavior,
 589     /// in cases where y == 0, or x == isize::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 == isize::MIN and y == -1
 597     pub fn unchecked_srem<T>(x: T, y: T) -> T;
 598     /// Returns the remainder of an unchecked unsigned division, which results in
 599     /// undefined behavior, in cases where y == 0
 600     pub fn unchecked_urem<T>(x: T, y: T) -> T;
 601
 602     /// Returns the value of the discriminant for the variant in 'v',
 603     /// cast to a `u64`; if `T` has no discriminant, returns 0.
 604     pub fn discriminant_value<T>(v: &T) -> u64;
 605
 606     /// Rust's "try catch" construct which invokes the function pointer `f` with
 607     /// the data pointer `data`, returning the exception payload if an exception
 608     /// is thrown (aka the thread panics).
 609     pub fn try(f: fn(*mut u8), data: *mut u8) -> *mut u8;
 610 }