ring/src/polyfill.rs

// Copyright 2015-2016 Brian Smith.
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR
// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

//! Polyfills for functionality that will (hopefully) be added to Rust's
//! standard library soon.

#![allow(unsafe_code)]

use core;

#[inline(always)]
pub fn u64_from_usize(x: usize) -> u64 {
    x as u64
}

/// `core::num::Wrapping` doesn't support `rotate_left`.
/// There is no usable trait for `rotate_left`, so this polyfill just hard-codes u32.
/// https://github.com/rust-lang/rust/issues/32463
#[inline(always)]
pub fn wrapping_rotate_left_u32(x: core::num::Wrapping<u32>, n: u32)
                            -> core::num::Wrapping<u32> {
    core::num::Wrapping(x.0.rotate_left(n))
}


pub mod slice {
    use core;

    #[inline(always)]
    pub fn u32_from_be_u8(buffer: &[u8; 4]) -> u32 {
        u32::from(buffer[0]) << 24 |
        u32::from(buffer[1]) << 16 |
        u32::from(buffer[2]) << 8 |
        u32::from(buffer[3])
    }

    // https://github.com/rust-lang/rust/issues/27750
    // https://internals.rust-lang.org/t/stabilizing-basic-functions-on-arrays-and-slices/2868
    #[inline(always)]
    pub fn fill(dest: &mut [u8], value: u8) {
        for d in dest {
            *d = value;
        }
    }

    // https://github.com/rust-lang/rust/issues/27750
    // https://internals.rust-lang.org/t/stabilizing-basic-functions-on-arrays-and-slices/2868
    #[inline(always)]
    pub fn fill_from_slice(dest: &mut [u8], src: &[u8]) {
        assert_eq!(dest.len(), src.len());
        unsafe {
            core::ptr::copy_nonoverlapping(src.as_ptr(), dest.as_mut_ptr(),
                                           src.len())
        }
    }

    // https://internals.rust-lang.org/t/safe-trasnsmute-for-slices-e-g-u64-u32-particularly-simd-types/2871
    #[inline(always)]
    pub fn u64_as_u8<'a>(src: &'a [u64]) -> &'a [u8] {
        unsafe {
            core::slice::from_raw_parts(src.as_ptr() as *const u8, src.len() * 8)
        }
    }

    // https://internals.rust-lang.org/t/safe-trasnsmute-for-slices-e-g-u64-u32-particularly-simd-types/2871
    #[inline(always)]
    pub fn u64_as_u8_mut<'a>(src: &'a mut [u64]) -> &'a mut [u8] {
        unsafe {
            core::slice::from_raw_parts_mut(src.as_mut_ptr() as *mut u8, src.len() * 8)
        }
    }

    // https://internals.rust-lang.org/t/safe-trasnsmute-for-slices-e-g-u64-u32-particularly-simd-types/2871
    #[inline(always)]
    pub fn u64_as_u32<'a>(src: &'a [u64]) -> &'a [u32] {
        unsafe {
            core::slice::from_raw_parts(src.as_ptr() as *const u32, src.len() * 2)
        }
    }

    // https://internals.rust-lang.org/t/safe-trasnsmute-for-slices-e-g-u64-u32-particularly-simd-types/2871
    #[inline(always)]
    pub fn u64_as_u32_mut<'a>(src: &'a mut [u64]) -> &'a mut [u32] {
        unsafe {
            core::slice::from_raw_parts_mut(src.as_mut_ptr() as *mut u32, src.len() * 2)
        }
    }

    #[inline(always)]
    pub fn as_wrapping_mut<'a, T>(src: &'a mut [T]) -> &'a mut [core::num::Wrapping<T>] {
        unsafe {
            core::slice::from_raw_parts_mut(
                src.as_mut_ptr() as *mut core::num::Wrapping<T>,
                src.len())
        }
    }
}

/// Returns a reference to the elements of `$slice` as an array, verifying that
/// the slice is of length `$len`.
macro_rules! slice_as_array_ref {
    ($slice:expr, $len:expr) => {
        {
            #[allow(unsafe_code)]
            fn slice_as_array_ref<'a, T>(slice: &'a [T])
                                         -> Result<&'a [T; $len], ()> {
                if slice.len() != $len {
                    return Err(());
                }
                Ok(unsafe {
                    &*(slice.as_ptr() as *const [T; $len])
                })
            }
            slice_as_array_ref($slice)
        }
    }
}

/// Returns a reference to elements of `$slice` as a mutable array, verifying
/// that the slice is of length `$len`.
macro_rules! slice_as_array_ref_mut {
    ($slice:expr, $len:expr) => {
        {
            #[allow(unsafe_code)]
            fn slice_as_array_ref<'a, T>(slice: &'a mut [T])
                                         -> Result<&'a mut [T; $len], ()> {
                if slice.len() != $len {
                    return Err(());
                }
                Ok(unsafe {
                    &mut *(slice.as_mut_ptr() as *mut [T; $len])
                })
            }
            slice_as_array_ref($slice)
        }
    }
}