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use crate::RngCore;
use core::cmp::min;
pub fn next_u64_via_u32<R: RngCore + ?Sized>(rng: &mut R) -> u64 {
let x = u64::from(rng.next_u32());
let y = u64::from(rng.next_u32());
(y << 32) | x
}
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! fill_via_chunks {
($src:expr, $dst:expr, $ty:ty) => {{
const SIZE: usize = core::mem::size_of::<$ty>();
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 {
core::ptr::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 {
core::ptr::copy_nonoverlapping(
src_ptr,
chunk.as_mut_ptr(),
chunk.len());
}
}
}
(chunk_size, chunk_size_u8)
}};
}
pub fn fill_via_u32_chunks(src: &[u32], dest: &mut [u8]) -> (usize, usize) {
fill_via_chunks!(src, dest, u32)
}
pub fn fill_via_u64_chunks(src: &[u64], dest: &mut [u8]) -> (usize, usize) {
fill_via_chunks!(src, dest, u64)
}
pub fn next_u32_via_fill<R: RngCore + ?Sized>(rng: &mut R) -> u32 {
let mut buf = [0; 4];
rng.fill_bytes(&mut buf);
u32::from_le_bytes(buf)
}
pub fn next_u64_via_fill<R: RngCore + ?Sized>(rng: &mut R) -> u64 {
let mut buf = [0; 8];
rng.fill_bytes(&mut buf);
u64::from_le_bytes(buf)
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn test_fill_via_u32_chunks() {
let src = [1, 2, 3];
let mut dst = [0u8; 11];
assert_eq!(fill_via_u32_chunks(&src, &mut dst), (3, 11));
assert_eq!(dst, [1, 0, 0, 0, 2, 0, 0, 0, 3, 0, 0]);
let mut dst = [0u8; 13];
assert_eq!(fill_via_u32_chunks(&src, &mut dst), (3, 12));
assert_eq!(dst, [1, 0, 0, 0, 2, 0, 0, 0, 3, 0, 0, 0, 0]);
let mut dst = [0u8; 5];
assert_eq!(fill_via_u32_chunks(&src, &mut dst), (2, 5));
assert_eq!(dst, [1, 0, 0, 0, 2]);
}
#[test]
fn test_fill_via_u64_chunks() {
let src = [1, 2];
let mut dst = [0u8; 11];
assert_eq!(fill_via_u64_chunks(&src, &mut dst), (2, 11));
assert_eq!(dst, [1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0]);
let mut dst = [0u8; 17];
assert_eq!(fill_via_u64_chunks(&src, &mut dst), (2, 16));
assert_eq!(dst, [1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0]);
let mut dst = [0u8; 5];
assert_eq!(fill_via_u64_chunks(&src, &mut dst), (1, 5));
assert_eq!(dst, [1, 0, 0, 0, 0]);
}
}