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const GF2_DIM: usize = 32;
fn gf2_matrix_times(mat: &[u32; GF2_DIM], mut vec: u32) -> u32 {
let mut sum = 0;
let mut idx = 0;
while vec > 0 {
if vec & 1 == 1 {
sum ^= mat[idx];
}
vec >>= 1;
idx += 1;
}
return sum;
}
fn gf2_matrix_square(square: &mut [u32; GF2_DIM], mat: &[u32; GF2_DIM]) {
for n in 0..GF2_DIM {
square[n] = gf2_matrix_times(mat, mat[n]);
}
}
pub(crate) fn combine(mut crc1: u32, crc2: u32, mut len2: u64) -> u32 {
let mut row: u32;
let mut even = [0u32; GF2_DIM]; /* even-power-of-two zeros operator */
let mut odd = [0u32; GF2_DIM]; /* odd-power-of-two zeros operator */
/* degenerate case (also disallow negative lengths) */
if len2 <= 0 {
return crc1;
}
/* put operator for one zero bit in odd */
odd[0] = 0xedb88320; /* CRC-32 polynomial */
row = 1;
for n in 1..GF2_DIM {
odd[n] = row;
row <<= 1;
}
/* put operator for two zero bits in even */
gf2_matrix_square(&mut even, &odd);
/* put operator for four zero bits in odd */
gf2_matrix_square(&mut odd, &even);
/* apply len2 zeros to crc1 (first square will put the operator for one
zero byte, eight zero bits, in even) */
loop {
/* apply zeros operator for this bit of len2 */
gf2_matrix_square(&mut even, &odd);
if len2 & 1 == 1 {
crc1 = gf2_matrix_times(&even, crc1);
}
len2 >>= 1;
/* if no more bits set, then done */
if len2 == 0 {
break;
}
/* another iteration of the loop with odd and even swapped */
gf2_matrix_square(&mut odd, &even);
if len2 & 1 == 1 {
crc1 = gf2_matrix_times(&odd, crc1);
}
len2 >>= 1;
/* if no more bits set, then done */
if len2 == 0 {
break;
}
}
/* return combined crc */
crc1 ^= crc2;
return crc1;
}