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 use core::convert::TryInto;
15
16 /// Reads unsigned 32 bit integers from `src` into `dst`.
17 #[inline]
read_u32_into(src: &[u8], dst: &mut [u32])18 pub fn read_u32_into(src: &[u8], dst: &mut [u32]) {
19 assert!(src.len() >= 4 * dst.len());
20 for (out, chunk) in dst.iter_mut().zip(src.chunks_exact(4)) {
21 *out = u32::from_le_bytes(chunk.try_into().unwrap());
22 }
23 }
24
25 /// Reads unsigned 64 bit integers from `src` into `dst`.
26 #[inline]
read_u64_into(src: &[u8], dst: &mut [u64])27 pub fn read_u64_into(src: &[u8], dst: &mut [u64]) {
28 assert!(src.len() >= 8 * dst.len());
29 for (out, chunk) in dst.iter_mut().zip(src.chunks_exact(8)) {
30 *out = u64::from_le_bytes(chunk.try_into().unwrap());
31 }
32 }
33
34 #[test]
test_read()35 fn test_read() {
36 let bytes = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16];
37
38 let mut buf = [0u32; 4];
39 read_u32_into(&bytes, &mut buf);
40 assert_eq!(buf[0], 0x04030201);
41 assert_eq!(buf[3], 0x100F0E0D);
42
43 let mut buf = [0u32; 3];
44 read_u32_into(&bytes[1..13], &mut buf); // unaligned
45 assert_eq!(buf[0], 0x05040302);
46 assert_eq!(buf[2], 0x0D0C0B0A);
47
48 let mut buf = [0u64; 2];
49 read_u64_into(&bytes, &mut buf);
50 assert_eq!(buf[0], 0x0807060504030201);
51 assert_eq!(buf[1], 0x100F0E0D0C0B0A09);
52
53 let mut buf = [0u64; 1];
54 read_u64_into(&bytes[7..15], &mut buf); // unaligned
55 assert_eq!(buf[0], 0x0F0E0D0C0B0A0908);
56 }
57