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use super::braid::CRC32_LSB_POLY;
pub const fn crc32_combine(crc1: u32, crc2: u32, len2: u64) -> u32 {
crc32_combine_op(crc1, crc2, crc32_combine_gen(len2))
}
#[inline(always)]
const fn crc32_combine_gen(len2: u64) -> u32 {
x2nmodp(len2, 3)
}
#[inline(always)]
const fn crc32_combine_op(crc1: u32, crc2: u32, op: u32) -> u32 {
multmodp(op, crc1) ^ crc2
}
const X2N_TABLE: [u32; 32] = [
0x40000000, 0x20000000, 0x08000000, 0x00800000, 0x00008000, 0xedb88320, 0xb1e6b092, 0xa06a2517,
0xed627dae, 0x88d14467, 0xd7bbfe6a, 0xec447f11, 0x8e7ea170, 0x6427800e, 0x4d47bae0, 0x09fe548f,
0x83852d0f, 0x30362f1a, 0x7b5a9cc3, 0x31fec169, 0x9fec022a, 0x6c8dedc4, 0x15d6874d, 0x5fde7a4e,
0xbad90e37, 0x2e4e5eef, 0x4eaba214, 0xa8a472c0, 0x429a969e, 0x148d302a, 0xc40ba6d0, 0xc4e22c3c,
];
// Return a(x) multiplied by b(x) modulo p(x), where p(x) is the CRC polynomial,
// reflected. For speed, this requires that a not be zero.
const fn multmodp(a: u32, mut b: u32) -> u32 {
let mut m = 1 << 31;
let mut p = 0;
loop {
if (a & m) != 0 {
p ^= b;
if (a & (m - 1)) == 0 {
break;
}
}
m >>= 1;
b = if (b & 1) != 0 {
(b >> 1) ^ CRC32_LSB_POLY as u32
} else {
b >> 1
};
}
p
}
// Return x^(n * 2^k) modulo p(x).
const fn x2nmodp(mut n: u64, mut k: u32) -> u32 {
let mut p: u32 = 1 << 31; /* x^0 == 1 */
while n > 0 {
if (n & 1) != 0 {
p = multmodp(X2N_TABLE[k as usize & 31], p);
}
n >>= 1;
k += 1;
}
p
}
#[cfg(test)]
mod test {
use super::*;
use crate::crc32;
#[test]
fn test_crc32_combine() {
::quickcheck::quickcheck(test as fn(_) -> _);
fn test(data: Vec<u8>) -> bool {
let Some(buf_len) = data.first().copied() else {
return true;
};
let buf_size = Ord::max(buf_len, 1) as usize;
let crc0 = 0;
let mut crc1 = crc0;
let mut crc2 = crc0;
/* CRC32 */
for chunk in data.chunks(buf_size) {
let crc3 = crc32(crc0, chunk);
let op = crc32_combine_gen(chunk.len() as _);
let crc4 = crc32_combine_op(crc1, crc3, op);
crc1 = crc32(crc1, chunk);
assert_eq!(crc1, crc4);
}
crc2 = crc32(crc2, &data);
assert_eq!(crc1, crc2);
let combine1 = crc32_combine(crc1, crc2, data.len() as _);
let combine2 = crc32_combine(crc1, crc1, data.len() as _);
assert_eq!(combine1, combine2);
// Fast CRC32 combine.
let op = crc32_combine_gen(data.len() as _);
let combine1 = crc32_combine_op(crc1, crc2, op);
let combine2 = crc32_combine_op(crc2, crc1, op);
assert_eq!(combine1, combine2);
let combine1 = crc32_combine(crc1, crc2, data.len() as _);
let combine2 = crc32_combine_op(crc2, crc1, op);
assert_eq!(combine1, combine2);
true
}
}
}