crc32fast/
baseline.rs

1use crate::table::CRC32_TABLE;
2
3#[derive(Clone)]
4pub struct State {
5    state: u32,
6}
7
8impl State {
9    pub fn new(state: u32) -> Self {
10        State { state }
11    }
12
13    pub fn update(&mut self, buf: &[u8]) {
14        self.state = update_fast_16(self.state, buf);
15    }
16
17    pub fn finalize(self) -> u32 {
18        self.state
19    }
20
21    pub fn reset(&mut self) {
22        self.state = 0;
23    }
24
25    pub fn combine(&mut self, other: u32, amount: u64) {
26        self.state = crate::combine::combine(self.state, other, amount);
27    }
28}
29
30/// Folds the first 16 bytes of `block` into `crc`.
31///
32/// `block` must be at least 16 bytes long. The decode is explicitly
33/// little-endian, so the result is identical on big-endian targets.
34#[inline(always)]
35fn fold_16(crc: u32, block: &[u8]) -> u32 {
36    let w0 = u32::from_le_bytes([block[0], block[1], block[2], block[3]]) ^ crc;
37    CRC32_TABLE[0x0][block[0xf] as usize]
38        ^ CRC32_TABLE[0x1][block[0xe] as usize]
39        ^ CRC32_TABLE[0x2][block[0xd] as usize]
40        ^ CRC32_TABLE[0x3][block[0xc] as usize]
41        ^ CRC32_TABLE[0x4][block[0xb] as usize]
42        ^ CRC32_TABLE[0x5][block[0xa] as usize]
43        ^ CRC32_TABLE[0x6][block[0x9] as usize]
44        ^ CRC32_TABLE[0x7][block[0x8] as usize]
45        ^ CRC32_TABLE[0x8][block[0x7] as usize]
46        ^ CRC32_TABLE[0x9][block[0x6] as usize]
47        ^ CRC32_TABLE[0xa][block[0x5] as usize]
48        ^ CRC32_TABLE[0xb][block[0x4] as usize]
49        ^ CRC32_TABLE[0xc][(w0 >> 24) as usize]
50        ^ CRC32_TABLE[0xd][((w0 >> 16) & 0xFF) as usize]
51        ^ CRC32_TABLE[0xe][((w0 >> 8) & 0xFF) as usize]
52        ^ CRC32_TABLE[0xf][(w0 & 0xFF) as usize]
53}
54
55pub(crate) fn update_fast_16(prev: u32, mut buf: &[u8]) -> u32 {
56    const UNROLL: usize = 4;
57    const BYTES_AT_ONCE: usize = 16 * UNROLL;
58
59    let mut crc = !prev;
60
61    while buf.len() >= BYTES_AT_ONCE {
62        for _ in 0..UNROLL {
63            crc = fold_16(crc, buf);
64            buf = &buf[16..];
65        }
66    }
67
68    // Fold whatever whole 16-byte blocks remain rather than handing them to the
69    // byte-at-a-time loop.
70    while buf.len() >= 16 {
71        crc = fold_16(crc, buf);
72        buf = &buf[16..];
73    }
74
75    update_slow(!crc, buf)
76}
77
78pub(crate) fn update_slow(prev: u32, buf: &[u8]) -> u32 {
79    let mut crc = !prev;
80
81    for &byte in buf.iter() {
82        crc = CRC32_TABLE[0][((crc as u8) ^ byte) as usize] ^ (crc >> 8);
83    }
84
85    !crc
86}
87
88#[cfg(test)]
89mod test {
90    #[test]
91    fn slow() {
92        assert_eq!(super::update_slow(0, b""), 0);
93
94        // test vectors from the iPXE project (input and output are bitwise negated)
95        assert_eq!(super::update_slow(!0x12345678, b""), !0x12345678);
96        assert_eq!(super::update_slow(!0xffffffff, b"hello world"), !0xf2b5ee7a);
97        assert_eq!(super::update_slow(!0xffffffff, b"hello"), !0xc9ef5979);
98        assert_eq!(super::update_slow(!0xc9ef5979, b" world"), !0xf2b5ee7a);
99
100        // Some vectors found on Rosetta code
101        assert_eq!(super::update_slow(0, b"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"), 0x190A55AD);
102        assert_eq!(super::update_slow(0, b"\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF"), 0xFF6CAB0B);
103        assert_eq!(super::update_slow(0, b"\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0A\x0B\x0C\x0D\x0E\x0F\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1A\x1B\x1C\x1D\x1E\x1F"), 0x91267E8A);
104    }
105
106    quickcheck::quickcheck! {
107        fn fast_16_is_the_same_as_slow(crc: u32, bytes: Vec<u8>) -> bool {
108            super::update_fast_16(crc, &bytes) == super::update_slow(crc, &bytes)
109        }
110    }
111}
crc32fast/baseline.rs

crc32fast/
baseline.rs
