1// Copyright 2018 Developers of the Rand project.
2//
3// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
4// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
5// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
6// option. This file may not be copied, modified, or distributed
7// except according to those terms.
8
9//! Little-Endian utilities
10//!
11//! Little-Endian order has been chosen for internal usage; this makes some
12//! useful functions available.
13
14/// Reads unsigned 32 bit integers from `src` into `dst`.
15///
16/// # Panics
17///
18/// If `dst` has insufficient space (`4*dst.len() < src.len()`).
19#[inline]
20#[track_caller]
21pub fn read_u32_into(src: &[u8], dst: &mut [u32]) {
22 assert!(src.len() >= 4 * dst.len());
23 for (out, chunk) in dst.iter_mut().zip(src.chunks_exact(4)) {
24 *out = u32::from_le_bytes(chunk.try_into().unwrap());
25 }
26}
27
28/// Reads unsigned 64 bit integers from `src` into `dst`.
29///
30/// # Panics
31///
32/// If `dst` has insufficient space (`8*dst.len() < src.len()`).
33#[inline]
34#[track_caller]
35pub fn read_u64_into(src: &[u8], dst: &mut [u64]) {
36 assert!(src.len() >= 8 * dst.len());
37 for (out, chunk) in dst.iter_mut().zip(src.chunks_exact(8)) {
38 *out = u64::from_le_bytes(chunk.try_into().unwrap());
39 }
40}
41
42#[test]
43fn test_read() {
44 let bytes: [i32; 16] = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16];
45
46 let mut buf: [u32; 4] = [0u32; 4];
47 read_u32_into(&bytes, &mut buf);
48 assert_eq!(buf[0], 0x04030201);
49 assert_eq!(buf[3], 0x100F0E0D);
50
51 let mut buf: [u32; _] = [0u32; 3];
52 read_u32_into(&bytes[1..13], &mut buf); // unaligned
53 assert_eq!(buf[0], 0x05040302);
54 assert_eq!(buf[2], 0x0D0C0B0A);
55
56 let mut buf: [u64; _] = [0u64; 2];
57 read_u64_into(&bytes, &mut buf);
58 assert_eq!(buf[0], 0x0807060504030201);
59 assert_eq!(buf[1], 0x100F0E0D0C0B0A09);
60
61 let mut buf: [u64; _] = [0u64; 1];
62 read_u64_into(&bytes[7..15], &mut buf); // unaligned
63 assert_eq!(buf[0], 0x0F0E0D0C0B0A0908);
64}
65