pqclean/crypto_kem/mceliece348864/avx2/vec.c

#include "vec.h"

/* input: v, an element in GF(2^m)[y]/(y^64+y^3+y+z) in bitsliced form */
/* input: a, an element in GF(2^m)[y]/(y^64+y^3+y+z) as an array of coefficients */
/* output: out, the product of v and a in bitsliced form */
void vec_GF_mul(vec out[ GFBITS ], vec v[ GFBITS ], gf a[ SYS_T ]) {
    int i, j;
    vec buf[GFBITS][2], prod[GFBITS], tmp[GFBITS];

    const vec allone = -1;

    // polynomial multiplication

    for (i = 0; i < GFBITS; i++) {
        buf[i][0] = 0;
        buf[i][1] = 0;
    }

    for (i = SYS_T - 1; i >= 0; i--) {
        for (j = 0; j < GFBITS; j++) {
            buf[j][1] <<= 1;
            buf[j][1] |= buf[j][0] >> 63;
            buf[j][0] <<= 1;
        }

        vec_mul_gf(prod, v, a[i]);

        for (j = 0; j < GFBITS; j++) {
            buf[j][0] ^= prod[j];
        }
    }

    // reduction modulo y^64 + y^3 + y + z

    for (i = 0; i < GFBITS; i++) {
        prod[i] = buf[i][1] & (allone << 3);
    }

    vec_mul_gf(tmp, prod, 2);

    for (i = 0; i < GFBITS; i++) {
        buf[i][1] ^= prod[i] >> (SYS_T - 3);
        buf[i][0] ^= prod[i] << (64 - (SYS_T - 3));
        buf[i][1] ^= prod[i] >> (SYS_T - 1);
        buf[i][0] ^= prod[i] << (64 - (SYS_T - 1));
        buf[i][0] ^= tmp[i];
    }

    //

    for (i = 0; i < GFBITS; i++) {
        prod[i] = buf[i][1] & 0x7;
    }

    vec_mul_gf(tmp, prod, 2);

    for (i = 0; i < GFBITS; i++) {
        buf[i][0] ^= prod[i] << (64 - (SYS_T - 3));
        buf[i][0] ^= prod[i] << (64 - (SYS_T - 1));
        buf[i][0] ^= tmp[i];
    }

    //

    for (i = 0; i < GFBITS; i++) {
        out[i] = buf[i][0];
    }
}