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times

Computes mat * vec over GF(2), where mat is a 32x32 binary matrix and vec is a 32-bit vector. This somewhat "simulates" how bits propagate through the CRC register during shifting.

In GF(2) (aka a field where the only values are 0 and 1, aka binary), multiplication is an AND, and addition is XOR.
This dot product determines how each bit in the input vector "contributes" to the final CRC state, by XORing (adding) rows of the matrix where vec has 1s.

Crc32c.times

fn times(mat: *const [32]u32, vec: u32) u32

File

lib/std/hash/crc/Crc32c.zig:114

Code

fn times(mat: *const [32]u32, vec: u32) u32 {
    var sum: u32 = 0;
    var v = vec;
    var i: u32 = 0;
    while (v != 0) {
        if (v & 1 != 0) sum ^= mat[i];
        v >>= 1;
        i += 1;
    }
    return sum;
}