pqcrypto/crypto_kem/ntruhps4096821/clean/sample.c

#include "sample.h"
#include "fips202.h"

void PQCLEAN_NTRUHPS4096821_CLEAN_sample_fg(poly *f, poly *g, const unsigned char uniformbytes[NTRU_SAMPLE_FG_BYTES]) {
    PQCLEAN_NTRUHPS4096821_CLEAN_sample_iid(f, uniformbytes);
    PQCLEAN_NTRUHPS4096821_CLEAN_sample_fixed_type(g, uniformbytes + NTRU_SAMPLE_IID_BYTES);
}

void PQCLEAN_NTRUHPS4096821_CLEAN_sample_rm(poly *r, poly *m, const unsigned char uniformbytes[NTRU_SAMPLE_RM_BYTES]) {
    PQCLEAN_NTRUHPS4096821_CLEAN_sample_iid(r, uniformbytes);
    PQCLEAN_NTRUHPS4096821_CLEAN_sample_fixed_type(m, uniformbytes + NTRU_SAMPLE_IID_BYTES);
}

void PQCLEAN_NTRUHPS4096821_CLEAN_sample_iid(poly *r, const unsigned char uniformbytes[NTRU_SAMPLE_IID_BYTES]) {
    int i;
    /* {0,1,...,255} -> {0,1,2}; Pr[0] = 86/256, Pr[1] = Pr[-1] = 85/256 */
    for (i = 0; i < NTRU_N - 1; i++) {
        r->coeffs[i] = PQCLEAN_NTRUHPS4096821_CLEAN_mod3(uniformbytes[i]);
    }

    r->coeffs[NTRU_N - 1] = 0;
}

#include "crypto_sort.h"
void PQCLEAN_NTRUHPS4096821_CLEAN_sample_fixed_type(poly *r, const unsigned char u[NTRU_SAMPLE_FT_BYTES]) {
    // Assumes NTRU_SAMPLE_FT_BYTES = ceil(30*(n-1)/8)

    int32_t s[NTRU_N - 1];
    int i;

    // Use 30 bits of u per word
    for (i = 0; i < (NTRU_N - 1) / 4; i++) {
        s[4 * i + 0] =                              (u[15 * i + 0] << 2) + (u[15 * i + 1] << 10) + (u[15 * i + 2] << 18) + (u[15 * i + 3] << 26);
        s[4 * i + 1] = ((u[15 * i + 3] & 0xc0) >> 4) + (u[15 * i + 4] << 4) + (u[15 * i + 5] << 12) + (u[15 * i + 6] << 20) + (u[15 * i + 7] << 28);
        s[4 * i + 2] = ((u[15 * i + 7] & 0xf0) >> 2) + (u[15 * i + 8] << 6) + (u[15 * i + 9] << 14) + (u[15 * i + 10] << 22) + (u[15 * i + 11] << 30);
        s[4 * i + 3] =  (u[15 * i + 11] & 0xfc)       + (u[15 * i + 12] << 8) + (u[15 * i + 13] << 15) + (u[15 * i + 14] << 24);
    }

    for (i = 0; i < NTRU_WEIGHT / 2; i++) {
        s[i] |=  1;
    }

    for (i = NTRU_WEIGHT / 2; i < NTRU_WEIGHT; i++) {
        s[i] |=  2;
    }

    PQCLEAN_NTRUHPS4096821_CLEAN_crypto_sort(s, NTRU_N - 1);

    for (i = 0; i < NTRU_N - 1; i++) {
        r->coeffs[i] = ((uint16_t) (s[i] & 3));
    }

    r->coeffs[NTRU_N - 1] = 0;
}