rust/src/libcore/intrinsics.rs

// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

/*! rustc compiler intrinsics.

The corresponding definitions are in librustc/middle/trans/foreign.rs.

# Volatiles

The volatile intrinsics provide operations intended to act on I/O
memory, which are guaranteed to not be reordered by the compiler
across other volatile intrinsics. See the LLVM documentation on
[[volatile]].

[volatile]: http://llvm.org/docs/LangRef.html#volatile-memory-accesses

# Atomics

The atomic intrinsics provide common atomic operations on machine
words, with multiple possible memory orderings. They obey the same
semantics as C++11. See the LLVM documentation on [[atomics]].

[atomics]: http://llvm.org/docs/Atomics.html

A quick refresher on memory ordering:

* Acquire - a barrier for acquiring a lock. Subsequent reads and writes
  take place after the barrier.
* Release - a barrier for releasing a lock. Preceding reads and writes
  take place before the barrier.
* Sequentially consistent - sequentially consistent operations are
  guaranteed to happen in order. This is the standard mode for working
  with atomic types and is equivalent to Java's `volatile`.

*/

#![experimental]
#![allow(missing_doc)]

pub type GlueFn = extern "Rust" fn(*const i8);

#[lang="ty_desc"]
pub struct TyDesc {
    // sizeof(T)
    pub size: uint,

    // alignof(T)
    pub align: uint,

    // Called when a value of type `T` is no longer needed
    pub drop_glue: GlueFn,

    // Called by reflection visitor to visit a value of type `T`
    pub visit_glue: GlueFn,

    // Name corresponding to the type
    pub name: &'static str,
}

#[lang="opaque"]
pub enum Opaque { }

pub type Disr = u64;

#[lang="ty_visitor"]
pub trait TyVisitor {
    fn visit_bot(&mut self) -> bool;
    fn visit_nil(&mut self) -> bool;
    fn visit_bool(&mut self) -> bool;

    fn visit_int(&mut self) -> bool;
    fn visit_i8(&mut self) -> bool;
    fn visit_i16(&mut self) -> bool;
    fn visit_i32(&mut self) -> bool;
    fn visit_i64(&mut self) -> bool;

    fn visit_uint(&mut self) -> bool;
    fn visit_u8(&mut self) -> bool;
    fn visit_u16(&mut self) -> bool;
    fn visit_u32(&mut self) -> bool;
    fn visit_u64(&mut self) -> bool;

    fn visit_f32(&mut self) -> bool;
    fn visit_f64(&mut self) -> bool;

    fn visit_char(&mut self) -> bool;

    fn visit_estr_slice(&mut self) -> bool;
    fn visit_estr_fixed(&mut self, n: uint, sz: uint, align: uint) -> bool;

    fn visit_box(&mut self, mtbl: uint, inner: *const TyDesc) -> bool;
    fn visit_uniq(&mut self, mtbl: uint, inner: *const TyDesc) -> bool;
    fn visit_ptr(&mut self, mtbl: uint, inner: *const TyDesc) -> bool;
    fn visit_rptr(&mut self, mtbl: uint, inner: *const TyDesc) -> bool;

    fn visit_evec_slice(&mut self, mtbl: uint, inner: *const TyDesc) -> bool;
    fn visit_evec_fixed(&mut self, n: uint, sz: uint, align: uint,
                        mtbl: uint, inner: *const TyDesc) -> bool;

    fn visit_enter_rec(&mut self, n_fields: uint,
                       sz: uint, align: uint) -> bool;
    fn visit_rec_field(&mut self, i: uint, name: &str,
                       mtbl: uint, inner: *const TyDesc) -> bool;
    fn visit_leave_rec(&mut self, n_fields: uint,
                       sz: uint, align: uint) -> bool;

    fn visit_enter_class(&mut self, name: &str, named_fields: bool, n_fields: uint,
                         sz: uint, align: uint) -> bool;
    fn visit_class_field(&mut self, i: uint, name: &str, named: bool,
                         mtbl: uint, inner: *const TyDesc) -> bool;
    fn visit_leave_class(&mut self, name: &str, named_fields: bool, n_fields: uint,
                         sz: uint, align: uint) -> bool;

    fn visit_enter_tup(&mut self, n_fields: uint,
                       sz: uint, align: uint) -> bool;
    fn visit_tup_field(&mut self, i: uint, inner: *const TyDesc) -> bool;
    fn visit_leave_tup(&mut self, n_fields: uint,
                       sz: uint, align: uint) -> bool;

    fn visit_enter_enum(&mut self, n_variants: uint,
                        get_disr: unsafe extern fn(ptr: *const Opaque) -> Disr,
                        sz: uint, align: uint) -> bool;
    fn visit_enter_enum_variant(&mut self, variant: uint,
                                disr_val: Disr,
                                n_fields: uint,
                                name: &str) -> bool;
    fn visit_enum_variant_field(&mut self, i: uint, offset: uint,
                                inner: *const TyDesc) -> bool;
    fn visit_leave_enum_variant(&mut self, variant: uint,
                                disr_val: Disr,
                                n_fields: uint,
                                name: &str) -> bool;
    fn visit_leave_enum(&mut self, n_variants: uint,
                        get_disr: unsafe extern fn(ptr: *const Opaque) -> Disr,
                        sz: uint, align: uint) -> bool;

    fn visit_enter_fn(&mut self, purity: uint, proto: uint,
                      n_inputs: uint, retstyle: uint) -> bool;
    fn visit_fn_input(&mut self, i: uint, mode: uint,
                      inner: *const TyDesc) -> bool;
    fn visit_fn_output(&mut self, retstyle: uint, variadic: bool,
                       inner: *const TyDesc) -> bool;
    fn visit_leave_fn(&mut self, purity: uint, proto: uint,
                      n_inputs: uint, retstyle: uint) -> bool;

    fn visit_trait(&mut self, name: &str) -> bool;
    fn visit_param(&mut self, i: uint) -> bool;
    fn visit_self(&mut self) -> bool;
}

extern "rust-intrinsic" {

    // NB: These intrinsics take unsafe pointers because they mutate aliased
    // memory, which is not valid for either `&` or `&mut`.

    pub fn atomic_cxchg<T>(dst: *mut T, old: T, src: T) -> T;
    pub fn atomic_cxchg_acq<T>(dst: *mut T, old: T, src: T) -> T;
    pub fn atomic_cxchg_rel<T>(dst: *mut T, old: T, src: T) -> T;
    pub fn atomic_cxchg_acqrel<T>(dst: *mut T, old: T, src: T) -> T;
    pub fn atomic_cxchg_relaxed<T>(dst: *mut T, old: T, src: T) -> T;

    pub fn atomic_load<T>(src: *const T) -> T;
    pub fn atomic_load_acq<T>(src: *const T) -> T;
    pub fn atomic_load_relaxed<T>(src: *const T) -> T;

    pub fn atomic_store<T>(dst: *mut T, val: T);
    pub fn atomic_store_rel<T>(dst: *mut T, val: T);
    pub fn atomic_store_relaxed<T>(dst: *mut T, val: T);

    pub fn atomic_xchg<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_xchg_acq<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_xchg_rel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_xchg_acqrel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_xchg_relaxed<T>(dst: *mut T, src: T) -> T;

    pub fn atomic_xadd<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_xadd_acq<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_xadd_rel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_xadd_acqrel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_xadd_relaxed<T>(dst: *mut T, src: T) -> T;

    pub fn atomic_xsub<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_xsub_acq<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_xsub_rel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_xsub_acqrel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_xsub_relaxed<T>(dst: *mut T, src: T) -> T;

    pub fn atomic_and<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_and_acq<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_and_rel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_and_acqrel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_and_relaxed<T>(dst: *mut T, src: T) -> T;

    pub fn atomic_nand<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_nand_acq<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_nand_rel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_nand_acqrel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_nand_relaxed<T>(dst: *mut T, src: T) -> T;

    pub fn atomic_or<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_or_acq<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_or_rel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_or_acqrel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_or_relaxed<T>(dst: *mut T, src: T) -> T;

    pub fn atomic_xor<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_xor_acq<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_xor_rel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_xor_acqrel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_xor_relaxed<T>(dst: *mut T, src: T) -> T;

    pub fn atomic_max<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_max_acq<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_max_rel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_max_acqrel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_max_relaxed<T>(dst: *mut T, src: T) -> T;

    pub fn atomic_min<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_min_acq<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_min_rel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_min_acqrel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_min_relaxed<T>(dst: *mut T, src: T) -> T;

    pub fn atomic_umin<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_umin_acq<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_umin_rel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_umin_acqrel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_umin_relaxed<T>(dst: *mut T, src: T) -> T;

    pub fn atomic_umax<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_umax_acq<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_umax_rel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_umax_acqrel<T>(dst: *mut T, src: T) -> T;
    pub fn atomic_umax_relaxed<T>(dst: *mut T, src: T) -> T;
}

extern "rust-intrinsic" {

    pub fn atomic_fence();
    pub fn atomic_fence_acq();
    pub fn atomic_fence_rel();
    pub fn atomic_fence_acqrel();

    /// Abort the execution of the process.
    pub fn abort() -> !;

    /// Execute a breakpoint trap, for inspection by a debugger.
    pub fn breakpoint();

    /// The size of a type in bytes.
    ///
    /// This is the exact number of bytes in memory taken up by a
    /// value of the given type. In other words, a memset of this size
    /// would *exactly* overwrite a value. When laid out in vectors
    /// and structures there may be additional padding between
    /// elements.
    pub fn size_of<T>() -> uint;

    /// Move a value to an uninitialized memory location.
    ///
    /// Drop glue is not run on the destination.
    pub fn move_val_init<T>(dst: &mut T, src: T);

    pub fn min_align_of<T>() -> uint;
    pub fn pref_align_of<T>() -> uint;

    /// Get a static pointer to a type descriptor.
    pub fn get_tydesc<T>() -> *const TyDesc;

    /// Gets an identifier which is globally unique to the specified type. This
    /// function will return the same value for a type regardless of whichever
    /// crate it is invoked in.
    pub fn type_id<T: 'static>() -> TypeId;


    /// Create a value initialized to zero.
    ///
    /// `init` is unsafe because it returns a zeroed-out datum,
    /// which is unsafe unless T is Copy.
    pub fn init<T>() -> T;

    /// Create an uninitialized value.
    pub fn uninit<T>() -> T;

    /// Move a value out of scope without running drop glue.
    ///
    /// `forget` is unsafe because the caller is responsible for
    /// ensuring the argument is deallocated already.
    pub fn forget<T>(_: T) -> ();

    /// Unsafely transforms a value of one type into a value of another type.
    ///
    /// Both types must have the same size and alignment, and this guarantee
    /// is enforced at compile-time.
    ///
    /// # Example
    ///
    /// ```rust
    /// use std::mem;
    ///
    /// let v: &[u8] = unsafe { mem::transmute("L") };
    /// assert!(v == [76u8]);
    /// ```
    pub fn transmute<T,U>(e: T) -> U;

    /// Gives the address for the return value of the enclosing function.
    ///
    /// Using this instrinsic in a function that does not use an out pointer
    /// will trigger a compiler error.
    pub fn return_address() -> *const u8;

    /// Returns `true` if a type requires drop glue.
    pub fn needs_drop<T>() -> bool;

    /// Returns `true` if a type is managed (will be allocated on the local heap)
    pub fn owns_managed<T>() -> bool;

    pub fn visit_tydesc(td: *const TyDesc, tv: &mut TyVisitor);

    /// Calculates the offset from a pointer. The offset *must* be in-bounds of
    /// the object, or one-byte-past-the-end. An arithmetic overflow is also
    /// undefined behaviour.
    ///
    /// This is implemented as an intrinsic to avoid converting to and from an
    /// integer, since the conversion would throw away aliasing information.
    pub fn offset<T>(dst: *const T, offset: int) -> *const T;

    /// Copies data from one location to another.
    ///
    /// Copies `count` elements (not bytes) from `src` to `dst`. The source
    /// and destination may *not* overlap.
    ///
    /// `copy_nonoverlapping_memory` is semantically equivalent to C's `memcpy`.
    ///
    /// # Example
    ///
    /// A safe swap function:
    ///
    /// ```
    /// use std::mem;
    /// use std::ptr;
    ///
    /// fn swap<T>(x: &mut T, y: &mut T) {
    ///     unsafe {
    ///         // Give ourselves some scratch space to work with
    ///         let mut t: T = mem::uninitialized();
    ///
    ///         // Perform the swap, `&mut` pointers never alias
    ///         ptr::copy_nonoverlapping_memory(&mut t, &*x, 1);
    ///         ptr::copy_nonoverlapping_memory(x, &*y, 1);
    ///         ptr::copy_nonoverlapping_memory(y, &t, 1);
    ///
    ///         // y and t now point to the same thing, but we need to completely forget `tmp`
    ///         // because it's no longer relevant.
    ///         mem::forget(t);
    ///     }
    /// }
    /// ```
    ///
    /// # Safety Note
    ///
    /// If the source and destination overlap then the behavior of this
    /// function is undefined.
    #[unstable]
    pub fn copy_nonoverlapping_memory<T>(dst: *mut T, src: *const T, count: uint);

    /// Copies data from one location to another.
    ///
    /// Copies `count` elements (not bytes) from `src` to `dst`. The source
    /// and destination may overlap.
    ///
    /// `copy_memory` is semantically equivalent to C's `memmove`.
    ///
    /// # Example
    ///
    /// Efficiently create a Rust vector from an unsafe buffer:
    ///
    /// ```
    /// use std::ptr;
    ///
    /// unsafe fn from_buf_raw<T>(ptr: *const T, elts: uint) -> Vec<T> {
    ///     let mut dst = Vec::with_capacity(elts);
    ///     dst.set_len(elts);
    ///     ptr::copy_memory(dst.as_mut_ptr(), ptr, elts);
    ///     dst
    /// }
    /// ```
    ///
    #[unstable]
    pub fn copy_memory<T>(dst: *mut T, src: *const T, count: uint);

    /// Invokes memset on the specified pointer, setting `count * size_of::<T>()`
    /// bytes of memory starting at `dst` to `c`.
    #[experimental = "uncertain about naming and semantics"]
    pub fn set_memory<T>(dst: *mut T, val: u8, count: uint);

    /// Equivalent to the appropriate `llvm.memcpy.p0i8.0i8.*` intrinsic, with
    /// a size of `count` * `size_of::<T>()` and an alignment of
    /// `min_align_of::<T>()`
    ///
    /// The volatile parameter parameter is set to `true`, so it will not be optimized out.
    pub fn volatile_copy_nonoverlapping_memory<T>(dst: *mut T, src: *const T,
                                                  count: uint);
    /// Equivalent to the appropriate `llvm.memmove.p0i8.0i8.*` intrinsic, with
    /// a size of `count` * `size_of::<T>()` and an alignment of
    /// `min_align_of::<T>()`
    ///
    /// The volatile parameter parameter is set to `true`, so it will not be optimized out.
    pub fn volatile_copy_memory<T>(dst: *mut T, src: *const T, count: uint);
    /// Equivalent to the appropriate `llvm.memset.p0i8.*` intrinsic, with a
    /// size of `count` * `size_of::<T>()` and an alignment of
    /// `min_align_of::<T>()`.
    ///
    /// The volatile parameter parameter is set to `true`, so it will not be optimized out.
    pub fn volatile_set_memory<T>(dst: *mut T, val: u8, count: uint);

    /// Perform a volatile load from the `src` pointer.
    pub fn volatile_load<T>(src: *const T) -> T;
    /// Perform a volatile store to the `dst` pointer.
    pub fn volatile_store<T>(dst: *mut T, val: T);

    /// Returns the square root of an `f32`
    pub fn sqrtf32(x: f32) -> f32;
    /// Returns the square root of an `f64`
    pub fn sqrtf64(x: f64) -> f64;

    /// Raises an `f32` to an integer power.
    pub fn powif32(a: f32, x: i32) -> f32;
    /// Raises an `f64` to an integer power.
    pub fn powif64(a: f64, x: i32) -> f64;

    /// Returns the sine of an `f32`.
    pub fn sinf32(x: f32) -> f32;
    /// Returns the sine of an `f64`.
    pub fn sinf64(x: f64) -> f64;

    /// Returns the cosine of an `f32`.
    pub fn cosf32(x: f32) -> f32;
    /// Returns the cosine of an `f64`.
    pub fn cosf64(x: f64) -> f64;

    /// Raises an `f32` to an `f32` power.
    pub fn powf32(a: f32, x: f32) -> f32;
    /// Raises an `f64` to an `f64` power.
    pub fn powf64(a: f64, x: f64) -> f64;

    /// Returns the exponential of an `f32`.
    pub fn expf32(x: f32) -> f32;
    /// Returns the exponential of an `f64`.
    pub fn expf64(x: f64) -> f64;

    /// Returns 2 raised to the power of an `f32`.
    pub fn exp2f32(x: f32) -> f32;
    /// Returns 2 raised to the power of an `f64`.
    pub fn exp2f64(x: f64) -> f64;

    /// Returns the natural logarithm of an `f32`.
    pub fn logf32(x: f32) -> f32;
    /// Returns the natural logarithm of an `f64`.
    pub fn logf64(x: f64) -> f64;

    /// Returns the base 10 logarithm of an `f32`.
    pub fn log10f32(x: f32) -> f32;
    /// Returns the base 10 logarithm of an `f64`.
    pub fn log10f64(x: f64) -> f64;

    /// Returns the base 2 logarithm of an `f32`.
    pub fn log2f32(x: f32) -> f32;
    /// Returns the base 2 logarithm of an `f64`.
    pub fn log2f64(x: f64) -> f64;

    /// Returns `a * b + c` for `f32` values.
    pub fn fmaf32(a: f32, b: f32, c: f32) -> f32;
    /// Returns `a * b + c` for `f64` values.
    pub fn fmaf64(a: f64, b: f64, c: f64) -> f64;

    /// Returns the absolute value of an `f32`.
    pub fn fabsf32(x: f32) -> f32;
    /// Returns the absolute value of an `f64`.
    pub fn fabsf64(x: f64) -> f64;

    /// Copies the sign from `y` to `x` for `f32` values.
    pub fn copysignf32(x: f32, y: f32) -> f32;
    /// Copies the sign from `y` to `x` for `f64` values.
    pub fn copysignf64(x: f64, y: f64) -> f64;

    /// Returns the largest integer less than or equal to an `f32`.
    pub fn floorf32(x: f32) -> f32;
    /// Returns the largest integer less than or equal to an `f64`.
    pub fn floorf64(x: f64) -> f64;

    /// Returns the smallest integer greater than or equal to an `f32`.
    pub fn ceilf32(x: f32) -> f32;
    /// Returns the smallest integer greater than or equal to an `f64`.
    pub fn ceilf64(x: f64) -> f64;

    /// Returns the integer part of an `f32`.
    pub fn truncf32(x: f32) -> f32;
    /// Returns the integer part of an `f64`.
    pub fn truncf64(x: f64) -> f64;

    /// Returns the nearest integer to an `f32`. May raise an inexact floating-point exception
    /// if the argument is not an integer.
    pub fn rintf32(x: f32) -> f32;
    /// Returns the nearest integer to an `f64`. May raise an inexact floating-point exception
    /// if the argument is not an integer.
    pub fn rintf64(x: f64) -> f64;

    /// Returns the nearest integer to an `f32`.
    pub fn nearbyintf32(x: f32) -> f32;
    /// Returns the nearest integer to an `f64`.
    pub fn nearbyintf64(x: f64) -> f64;

    /// Returns the nearest integer to an `f32`. Rounds half-way cases away from zero.
    pub fn roundf32(x: f32) -> f32;
    /// Returns the nearest integer to an `f64`. Rounds half-way cases away from zero.
    pub fn roundf64(x: f64) -> f64;

    /// Returns the number of bits set in a `u8`.
    pub fn ctpop8(x: u8) -> u8;
    /// Returns the number of bits set in a `u16`.
    pub fn ctpop16(x: u16) -> u16;
    /// Returns the number of bits set in a `u32`.
    pub fn ctpop32(x: u32) -> u32;
    /// Returns the number of bits set in a `u64`.
    pub fn ctpop64(x: u64) -> u64;

    /// Returns the number of leading bits unset in a `u8`.
    pub fn ctlz8(x: u8) -> u8;
    /// Returns the number of leading bits unset in a `u16`.
    pub fn ctlz16(x: u16) -> u16;
    /// Returns the number of leading bits unset in a `u32`.
    pub fn ctlz32(x: u32) -> u32;
    /// Returns the number of leading bits unset in a `u64`.
    pub fn ctlz64(x: u64) -> u64;

    /// Returns the number of trailing bits unset in a `u8`.
    pub fn cttz8(x: u8) -> u8;
    /// Returns the number of trailing bits unset in a `u16`.
    pub fn cttz16(x: u16) -> u16;
    /// Returns the number of trailing bits unset in a `u32`.
    pub fn cttz32(x: u32) -> u32;
    /// Returns the number of trailing bits unset in a `u64`.
    pub fn cttz64(x: u64) -> u64;

    /// Reverses the bytes in a `u16`.
    pub fn bswap16(x: u16) -> u16;
    /// Reverses the bytes in a `u32`.
    pub fn bswap32(x: u32) -> u32;
    /// Reverses the bytes in a `u64`.
    pub fn bswap64(x: u64) -> u64;

    /// Performs checked `i8` addition.
    pub fn i8_add_with_overflow(x: i8, y: i8) -> (i8, bool);
    /// Performs checked `i16` addition.
    pub fn i16_add_with_overflow(x: i16, y: i16) -> (i16, bool);
    /// Performs checked `i32` addition.
    pub fn i32_add_with_overflow(x: i32, y: i32) -> (i32, bool);
    /// Performs checked `i64` addition.
    pub fn i64_add_with_overflow(x: i64, y: i64) -> (i64, bool);

    /// Performs checked `u8` addition.
    pub fn u8_add_with_overflow(x: u8, y: u8) -> (u8, bool);
    /// Performs checked `u16` addition.
    pub fn u16_add_with_overflow(x: u16, y: u16) -> (u16, bool);
    /// Performs checked `u32` addition.
    pub fn u32_add_with_overflow(x: u32, y: u32) -> (u32, bool);
    /// Performs checked `u64` addition.
    pub fn u64_add_with_overflow(x: u64, y: u64) -> (u64, bool);

    /// Performs checked `i8` subtraction.
    pub fn i8_sub_with_overflow(x: i8, y: i8) -> (i8, bool);
    /// Performs checked `i16` subtraction.
    pub fn i16_sub_with_overflow(x: i16, y: i16) -> (i16, bool);
    /// Performs checked `i32` subtraction.
    pub fn i32_sub_with_overflow(x: i32, y: i32) -> (i32, bool);
    /// Performs checked `i64` subtraction.
    pub fn i64_sub_with_overflow(x: i64, y: i64) -> (i64, bool);

    /// Performs checked `u8` subtraction.
    pub fn u8_sub_with_overflow(x: u8, y: u8) -> (u8, bool);
    /// Performs checked `u16` subtraction.
    pub fn u16_sub_with_overflow(x: u16, y: u16) -> (u16, bool);
    /// Performs checked `u32` subtraction.
    pub fn u32_sub_with_overflow(x: u32, y: u32) -> (u32, bool);
    /// Performs checked `u64` subtraction.
    pub fn u64_sub_with_overflow(x: u64, y: u64) -> (u64, bool);

    /// Performs checked `i8` multiplication.
    pub fn i8_mul_with_overflow(x: i8, y: i8) -> (i8, bool);
    /// Performs checked `i16` multiplication.
    pub fn i16_mul_with_overflow(x: i16, y: i16) -> (i16, bool);
    /// Performs checked `i32` multiplication.
    pub fn i32_mul_with_overflow(x: i32, y: i32) -> (i32, bool);
    /// Performs checked `i64` multiplication.
    pub fn i64_mul_with_overflow(x: i64, y: i64) -> (i64, bool);

    /// Performs checked `u8` multiplication.
    pub fn u8_mul_with_overflow(x: u8, y: u8) -> (u8, bool);
    /// Performs checked `u16` multiplication.
    pub fn u16_mul_with_overflow(x: u16, y: u16) -> (u16, bool);
    /// Performs checked `u32` multiplication.
    pub fn u32_mul_with_overflow(x: u32, y: u32) -> (u32, bool);
    /// Performs checked `u64` multiplication.
    pub fn u64_mul_with_overflow(x: u64, y: u64) -> (u64, bool);
}


/// `TypeId` represents a globally unique identifier for a type
#[lang="type_id"] // This needs to be kept in lockstep with the code in trans/intrinsic.rs and
                  // middle/lang_items.rs
#[deriving(PartialEq, Eq, Show)]
pub struct TypeId {
    t: u64,
}

impl TypeId {
    /// Returns the `TypeId` of the type this generic function has been instantiated with
    pub fn of<T: 'static>() -> TypeId {
        unsafe { type_id::<T>() }
    }
    pub fn hash(&self) -> u64 { self.t }
}