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Diffstat (limited to 'rand/rand_core/src/impls.rs')
| -rw-r--r-- | rand/rand_core/src/impls.rs | 158 |
1 files changed, 0 insertions, 158 deletions
diff --git a/rand/rand_core/src/impls.rs b/rand/rand_core/src/impls.rs deleted file mode 100644 index dee4ed1..0000000 --- a/rand/rand_core/src/impls.rs +++ /dev/null @@ -1,158 +0,0 @@ -// Copyright 2018 Developers of the Rand project. -// -// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or -// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license -// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your -// option. This file may not be copied, modified, or distributed -// except according to those terms. - -//! Helper functions for implementing `RngCore` functions. -//! -//! For cross-platform reproducibility, these functions all use Little Endian: -//! least-significant part first. For example, `next_u64_via_u32` takes `u32` -//! values `x, y`, then outputs `(y << 32) | x`. To implement `next_u32` -//! from `next_u64` in little-endian order, one should use `next_u64() as u32`. -//! -//! Byte-swapping (like the std `to_le` functions) is only needed to convert -//! to/from byte sequences, and since its purpose is reproducibility, -//! non-reproducible sources (e.g. `OsRng`) need not bother with it. - -use core::ptr::copy_nonoverlapping; -use core::slice; -use core::cmp::min; -use core::mem::size_of; -use crate::RngCore; - - -/// Implement `next_u64` via `next_u32`, little-endian order. -pub fn next_u64_via_u32<R: RngCore + ?Sized>(rng: &mut R) -> u64 { - // Use LE; we explicitly generate one value before the next. - let x = u64::from(rng.next_u32()); - let y = u64::from(rng.next_u32()); - (y << 32) | x -} - -/// Implement `fill_bytes` via `next_u64` and `next_u32`, little-endian order. -/// -/// The fastest way to fill a slice is usually to work as long as possible with -/// integers. That is why this method mostly uses `next_u64`, and only when -/// there are 4 or less bytes remaining at the end of the slice it uses -/// `next_u32` once. -pub fn fill_bytes_via_next<R: RngCore + ?Sized>(rng: &mut R, dest: &mut [u8]) { - let mut left = dest; - while left.len() >= 8 { - let (l, r) = {left}.split_at_mut(8); - left = r; - let chunk: [u8; 8] = rng.next_u64().to_le_bytes(); - l.copy_from_slice(&chunk); - } - let n = left.len(); - if n > 4 { - let chunk: [u8; 8] = rng.next_u64().to_le_bytes(); - left.copy_from_slice(&chunk[..n]); - } else if n > 0 { - let chunk: [u8; 4] = rng.next_u32().to_le_bytes(); - left.copy_from_slice(&chunk[..n]); - } -} - -macro_rules! impl_uint_from_fill { - ($rng:expr, $ty:ty, $N:expr) => ({ - debug_assert!($N == size_of::<$ty>()); - - let mut int: $ty = 0; - unsafe { - let ptr = &mut int as *mut $ty as *mut u8; - let slice = slice::from_raw_parts_mut(ptr, $N); - $rng.fill_bytes(slice); - } - int - }); -} - -macro_rules! fill_via_chunks { - ($src:expr, $dst:expr, $ty:ty, $size:expr) => ({ - let chunk_size_u8 = min($src.len() * $size, $dst.len()); - let chunk_size = (chunk_size_u8 + $size - 1) / $size; - if cfg!(target_endian="little") { - unsafe { - copy_nonoverlapping( - $src.as_ptr() as *const u8, - $dst.as_mut_ptr(), - chunk_size_u8); - } - } else { - for (&n, chunk) in $src.iter().zip($dst.chunks_mut($size)) { - let tmp = n.to_le(); - let src_ptr = &tmp as *const $ty as *const u8; - unsafe { - copy_nonoverlapping(src_ptr, - chunk.as_mut_ptr(), - chunk.len()); - } - } - } - - (chunk_size, chunk_size_u8) - }); -} - -/// Implement `fill_bytes` by reading chunks from the output buffer of a block -/// based RNG. -/// -/// The return values are `(consumed_u32, filled_u8)`. -/// -/// `filled_u8` is the number of filled bytes in `dest`, which may be less than -/// the length of `dest`. -/// `consumed_u32` is the number of words consumed from `src`, which is the same -/// as `filled_u8 / 4` rounded up. -/// -/// # Example -/// (from `IsaacRng`) -/// -/// ```ignore -/// fn fill_bytes(&mut self, dest: &mut [u8]) { -/// let mut read_len = 0; -/// while read_len < dest.len() { -/// if self.index >= self.rsl.len() { -/// self.isaac(); -/// } -/// -/// let (consumed_u32, filled_u8) = -/// impls::fill_via_u32_chunks(&mut self.rsl[self.index..], -/// &mut dest[read_len..]); -/// -/// self.index += consumed_u32; -/// read_len += filled_u8; -/// } -/// } -/// ``` -pub fn fill_via_u32_chunks(src: &[u32], dest: &mut [u8]) -> (usize, usize) { - fill_via_chunks!(src, dest, u32, 4) -} - -/// Implement `fill_bytes` by reading chunks from the output buffer of a block -/// based RNG. -/// -/// The return values are `(consumed_u64, filled_u8)`. -/// `filled_u8` is the number of filled bytes in `dest`, which may be less than -/// the length of `dest`. -/// `consumed_u64` is the number of words consumed from `src`, which is the same -/// as `filled_u8 / 8` rounded up. -/// -/// See `fill_via_u32_chunks` for an example. -pub fn fill_via_u64_chunks(src: &[u64], dest: &mut [u8]) -> (usize, usize) { - fill_via_chunks!(src, dest, u64, 8) -} - -/// Implement `next_u32` via `fill_bytes`, little-endian order. -pub fn next_u32_via_fill<R: RngCore + ?Sized>(rng: &mut R) -> u32 { - impl_uint_from_fill!(rng, u32, 4) -} - -/// Implement `next_u64` via `fill_bytes`, little-endian order. -pub fn next_u64_via_fill<R: RngCore + ?Sized>(rng: &mut R) -> u64 { - impl_uint_from_fill!(rng, u64, 8) -} - -// TODO: implement tests for the above |