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