pqc/crypto_kem/firesaber/clean/poly_mul.c

#include "poly.h"
#include <stdint.h>
#include <string.h>

#define SCHB_N 16

#define N_RES (SABER_N << 1)
#define N_SB (SABER_N >> 2)
#define N_SB_RES (2*N_SB-1)

#define OVERFLOWING_MUL(X, Y) ((uint16_t)((uint32_t)(X) * (uint32_t)(Y)))

#define KARATSUBA_N 64
static void karatsuba_simple(uint16_t *result_final, const uint16_t *a_1, const uint16_t *b_1) {
    uint16_t d01[KARATSUBA_N / 2 - 1];
    uint16_t d0123[KARATSUBA_N / 2 - 1];
    uint16_t d23[KARATSUBA_N / 2 - 1];
    uint16_t result_d01[KARATSUBA_N - 1];

    size_t i, j;

    memset(result_d01, 0, (KARATSUBA_N - 1)*sizeof(uint16_t));
    memset(d01, 0, (KARATSUBA_N / 2 - 1)*sizeof(uint16_t));
    memset(d0123, 0, (KARATSUBA_N / 2 - 1)*sizeof(uint16_t));
    memset(d23, 0, (KARATSUBA_N / 2 - 1)*sizeof(uint16_t));
    memset(result_final, 0, (2 * KARATSUBA_N - 1)*sizeof(uint16_t));

    uint16_t acc1, acc2, acc3, acc4, acc5, acc6, acc7, acc8, acc9, acc10;


    for (i = 0; i < KARATSUBA_N / 4; i++) {
        acc1 = a_1[i]; //a0
        acc2 = a_1[i + KARATSUBA_N / 4]; //a1
        acc3 = a_1[i + 2 * KARATSUBA_N / 4]; //a2
        acc4 = a_1[i + 3 * KARATSUBA_N / 4]; //a3
        for (j = 0; j < KARATSUBA_N / 4; j++) {

            acc5 = b_1[j]; //b0
            acc6 = b_1[j + KARATSUBA_N / 4]; //b1

            result_final[i + j + 0 * KARATSUBA_N / 4] =
                result_final[i + j + 0 * KARATSUBA_N / 4] +
                OVERFLOWING_MUL(acc1, acc5);
            result_final[i + j + 2 * KARATSUBA_N / 4] =
                result_final[i + j + 2 * KARATSUBA_N / 4] +
                OVERFLOWING_MUL(acc2, acc6);

            acc7 = acc5 + acc6; //b01
            acc8 = acc1 + acc2; //a01
            d01[i + j] = d01[i + j] + (uint16_t)(acc7 * (uint64_t)acc8);
            //--------------------------------------------------------

            acc7 = b_1[j + 2 * KARATSUBA_N / 4]; //b2
            acc8 = b_1[j + 3 * KARATSUBA_N / 4]; //b3
            result_final[i + j + 4 * KARATSUBA_N / 4] =
                result_final[i + j + 4 * KARATSUBA_N / 4] +
                OVERFLOWING_MUL(acc7, acc3);

            result_final[i + j + 6 * KARATSUBA_N / 4] =
                result_final[i + j + 6 * KARATSUBA_N / 4] +
                OVERFLOWING_MUL(acc8, acc4);

            acc9 = acc3 + acc4;
            acc10 = acc7 + acc8;
            d23[i + j] = d23[i + j] + OVERFLOWING_MUL(acc9, acc10);
            //--------------------------------------------------------

            acc5 = acc5 + acc7; //b02
            acc7 = acc1 + acc3; //a02
            result_d01[i + j + 0 * KARATSUBA_N / 4] =
                result_d01[i + j + 0 * KARATSUBA_N / 4] +
                OVERFLOWING_MUL(acc5, acc7);

            acc6 = acc6 + acc8; //b13
            acc8 = acc2 + acc4;
            result_d01[i + j + 2 * KARATSUBA_N / 4] =
                result_d01[i + j + 2 * KARATSUBA_N / 4] +
                OVERFLOWING_MUL(acc6, acc8);

            acc5 = acc5 + acc6;
            acc7 = acc7 + acc8;
            d0123[i + j] = d0123[i + j] + OVERFLOWING_MUL(acc5, acc7);
        }
    }

    // 2nd last stage

    for (i = 0; i < KARATSUBA_N / 2 - 1; i++) {
        d0123[i] = d0123[i] - result_d01[i + 0 * KARATSUBA_N / 4] - result_d01[i + 2 * KARATSUBA_N / 4];
        d01[i] = d01[i] - result_final[i + 0 * KARATSUBA_N / 4] - result_final[i + 2 * KARATSUBA_N / 4];
        d23[i] = d23[i] - result_final[i + 4 * KARATSUBA_N / 4] - result_final[i + 6 * KARATSUBA_N / 4];
    }

    for (i = 0; i < KARATSUBA_N / 2 - 1; i++) {
        result_d01[i + 1 * KARATSUBA_N / 4] = result_d01[i + 1 * KARATSUBA_N / 4] + d0123[i];
        result_final[i + 1 * KARATSUBA_N / 4] = result_final[i + 1 * KARATSUBA_N / 4] + d01[i];
        result_final[i + 5 * KARATSUBA_N / 4] = result_final[i + 5 * KARATSUBA_N / 4] + d23[i];
    }

    // Last stage
    for (i = 0; i < KARATSUBA_N - 1; i++) {
        result_d01[i] = result_d01[i] - result_final[i] - result_final[i + KARATSUBA_N];
    }

    for (i = 0; i < KARATSUBA_N - 1; i++) {
        result_final[i + 1 * KARATSUBA_N / 2] = result_final[i + 1 * KARATSUBA_N / 2] + result_d01[i];
    }

}



static void toom_cook_4way (uint16_t *result, const uint16_t *a1, const uint16_t *b1) {
    uint16_t inv3 = 43691, inv9 = 36409, inv15 = 61167;

    uint16_t aw1[N_SB], aw2[N_SB], aw3[N_SB], aw4[N_SB], aw5[N_SB], aw6[N_SB], aw7[N_SB];
    uint16_t bw1[N_SB], bw2[N_SB], bw3[N_SB], bw4[N_SB], bw5[N_SB], bw6[N_SB], bw7[N_SB];
    uint16_t w1[N_SB_RES] = {0}, w2[N_SB_RES] = {0}, w3[N_SB_RES] = {0}, w4[N_SB_RES] = {0},
                            w5[N_SB_RES] = {0}, w6[N_SB_RES] = {0}, w7[N_SB_RES] = {0};
    uint16_t r0, r1, r2, r3, r4, r5, r6, r7;
    uint16_t *A0, *A1, *A2, *A3, *B0, *B1, *B2, *B3;
    A0 = (uint16_t *)a1;
    A1 = (uint16_t *)&a1[N_SB];
    A2 = (uint16_t *)&a1[2 * N_SB];
    A3 = (uint16_t *)&a1[3 * N_SB];
    B0 = (uint16_t *)b1;
    B1 = (uint16_t *)&b1[N_SB];
    B2 = (uint16_t *)&b1[2 * N_SB];
    B3 = (uint16_t *)&b1[3 * N_SB];

    uint16_t *C;
    C = result;

    int i, j;

    // EVALUATION
    for (j = 0; j < N_SB; ++j) {
        r0 = A0[j];
        r1 = A1[j];
        r2 = A2[j];
        r3 = A3[j];
        r4 = r0 + r2;
        r5 = r1 + r3;
        r6 = r4 + r5;
        r7 = r4 - r5;
        aw3[j] = r6;
        aw4[j] = r7;
        r4 = ((r0 << 2) + r2) << 1;
        r5 = (r1 << 2) + r3;
        r6 = r4 + r5;
        r7 = r4 - r5;
        aw5[j] = r6;
        aw6[j] = r7;
        r4 = (r3 << 3) + (r2 << 2) + (r1 << 1) + r0;
        aw2[j] = r4;
        aw7[j] = r0;
        aw1[j] = r3;
    }
    for (j = 0; j < N_SB; ++j) {
        r0 = B0[j];
        r1 = B1[j];
        r2 = B2[j];
        r3 = B3[j];
        r4 = r0 + r2;
        r5 = r1 + r3;
        r6 = r4 + r5;
        r7 = r4 - r5;
        bw3[j] = r6;
        bw4[j] = r7;
        r4 = ((r0 << 2) + r2) << 1;
        r5 = (r1 << 2) + r3;
        r6 = r4 + r5;
        r7 = r4 - r5;
        bw5[j] = r6;
        bw6[j] = r7;
        r4 = (r3 << 3) + (r2 << 2) + (r1 << 1) + r0;
        bw2[j] = r4;
        bw7[j] = r0;
        bw1[j] = r3;
    }

    // MULTIPLICATION

    karatsuba_simple(w1, aw1, bw1);
    karatsuba_simple(w2, aw2, bw2);
    karatsuba_simple(w3, aw3, bw3);
    karatsuba_simple(w4, aw4, bw4);
    karatsuba_simple(w5, aw5, bw5);
    karatsuba_simple(w6, aw6, bw6);
    karatsuba_simple(w7, aw7, bw7);

    // INTERPOLATION
    for (i = 0; i < N_SB_RES; ++i) {
        r0 = w1[i];
        r1 = w2[i];
        r2 = w3[i];
        r3 = w4[i];
        r4 = w5[i];
        r5 = w6[i];
        r6 = w7[i];

        r1 = r1 + r4;
        r5 = r5 - r4;
        r3 = ((r3 - r2) >> 1);
        r4 = r4 - r0;
        r4 = r4 - (r6 << 6);
        r4 = (r4 << 1) + r5;
        r2 = r2 + r3;
        r1 = r1 - (r2 << 6) - r2;
        r2 = r2 - r6;
        r2 = r2 - r0;
        r1 = r1 + 45 * r2;
        r4 = (uint16_t)(((r4 - (r2 << 3)) * (uint32_t)inv3) >> 3);
        r5 = r5 + r1;
        r1 = (uint16_t)(((r1 + (r3 << 4)) * (uint32_t)inv9) >> 1);
        r3 = -(r3 + r1);
        r5 = (uint16_t)(((30 * r1 - r5) * (uint32_t)inv15) >> 2);
        r2 = r2 - r4;
        r1 = r1 - r5;

        C[i]     += r6;
        C[i + 64]  += r5;
        C[i + 128] += r4;
        C[i + 192] += r3;
        C[i + 256] += r2;
        C[i + 320] += r1;
        C[i + 384] += r0;
    }
}

/* res += a*b */
void PQCLEAN_FIRESABER_CLEAN_poly_mul(poly *c, const poly *a, const poly *b, const int accumulate) {
    uint16_t C[2 * SABER_N] = {0};
    size_t i;

    toom_cook_4way(C, a->coeffs, b->coeffs);

    /* reduction */
    if (accumulate == 0) {
        for (i = SABER_N; i < 2 * SABER_N; i++) {
            c->coeffs[i - SABER_N] = (C[i - SABER_N] - C[i]);
        }
    } else {
        for (i = SABER_N; i < 2 * SABER_N; i++) {
            c->coeffs[i - SABER_N] += (C[i - SABER_N] - C[i]);
        }
    }
}