67 lines
1.2 KiB
Rust
67 lines
1.2 KiB
Rust
//! Checksum functions.
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// Accumulator for CRC function.
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fn crc_accum(a: u32, _: u32) -> u32
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{
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if a & 1 == 1 {
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ISO_3309_POLYNOMIAL ^ a >> 1
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} else {
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a >> 1
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}
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}
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// Initializes a CRC array.
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// FIXME: use const fn when stabilized
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fn crc_init() -> [u32; 256]
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{
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let mut t = [0; 256];
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for (n, v) in t.iter_mut().enumerate() {
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*v = (0..8).fold(n as u32, crc_accum);
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}
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t
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}
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/// Creates an ADLER32 of all bytes in `b`.
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///
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/// # Examples
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///
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/// ```
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/// use maraiah::cksum::adler32;
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///
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/// assert_eq!(adler32(b"Lorem ipsum dolor sit amet"), 0x83D5_09C5);
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/// ```
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pub fn adler32(b: &[u8]) -> u32
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{
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let mut x = 1;
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let mut y = 0;
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for &z in b {
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let z = u32::from(z);
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x = (x + z) % ADLER32_MODULO;
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y = (y + x) % ADLER32_MODULO;
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}
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(y << 16) | x
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}
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/// Creates a CRC-32 of all bytes in `b` with the starting sum `s`. The
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/// polynomial used is the one from ISO-3309.
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///
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/// # Examples
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///
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/// ```
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/// use maraiah::cksum::crc32;
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///
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/// assert_eq!(crc32(b"Lorem ipsum dolor sit amet", !0), 0x5F29_D461);
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/// ```
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pub fn crc32(b: &[u8], s: u32) -> u32
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{
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let t = crc_init();
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!b.iter().fold(s, |a, &o| a >> 8 ^ t[usize::from(a as u8 ^ o)])
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}
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const ISO_3309_POLYNOMIAL: u32 = 0xEDB8_8320;
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const ADLER32_MODULO: u32 = 0xFFF1;
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// EOF
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