79 lines
2.2 KiB
C
79 lines
2.2 KiB
C
/* Based on supercop-20200702/crypto_core/invhrss701/simpler/core.c */
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#include "poly.h"
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static inline uint8_t mod3(uint8_t a) { /* a between 0 and 9 */
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int16_t t, c;
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a = (a >> 2) + (a & 3); /* between 0 and 4 */
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t = a - 3;
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c = t >> 5;
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return (uint8_t) (t ^ (c & (a ^ t)));
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}
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/* return -1 if x<0 and y<0; otherwise return 0 */
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static inline int16_t both_negative_mask(int16_t x, int16_t y) {
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return (x & y) >> 15;
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}
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void PQCLEAN_NTRUHPS2048677_CLEAN_poly_S3_inv(poly *r, const poly *a) {
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poly f, g, v, w;
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size_t i, loop;
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int16_t delta, sign, swap, t;
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for (i = 0; i < NTRU_N; ++i) {
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v.coeffs[i] = 0;
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}
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for (i = 0; i < NTRU_N; ++i) {
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w.coeffs[i] = 0;
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}
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w.coeffs[0] = 1;
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for (i = 0; i < NTRU_N; ++i) {
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f.coeffs[i] = 1;
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}
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for (i = 0; i < NTRU_N - 1; ++i) {
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g.coeffs[NTRU_N - 2 - i] = mod3((a->coeffs[i] & 3) + 2 * (a->coeffs[NTRU_N - 1] & 3));
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}
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g.coeffs[NTRU_N - 1] = 0;
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delta = 1;
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for (loop = 0; loop < 2 * (NTRU_N - 1) - 1; ++loop) {
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for (i = NTRU_N - 1; i > 0; --i) {
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v.coeffs[i] = v.coeffs[i - 1];
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}
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v.coeffs[0] = 0;
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sign = mod3((uint8_t) (2 * g.coeffs[0] * f.coeffs[0]));
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swap = both_negative_mask(-delta, -(int16_t) g.coeffs[0]);
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delta ^= swap & (delta ^ -delta);
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delta += 1;
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for (i = 0; i < NTRU_N; ++i) {
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t = swap & (f.coeffs[i] ^ g.coeffs[i]);
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f.coeffs[i] ^= t;
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g.coeffs[i] ^= t;
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t = swap & (v.coeffs[i] ^ w.coeffs[i]);
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v.coeffs[i] ^= t;
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w.coeffs[i] ^= t;
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}
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for (i = 0; i < NTRU_N; ++i) {
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g.coeffs[i] = mod3((uint8_t) (g.coeffs[i] + sign * f.coeffs[i]));
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}
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for (i = 0; i < NTRU_N; ++i) {
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w.coeffs[i] = mod3((uint8_t) (w.coeffs[i] + sign * v.coeffs[i]));
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}
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for (i = 0; i < NTRU_N - 1; ++i) {
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g.coeffs[i] = g.coeffs[i + 1];
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}
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g.coeffs[NTRU_N - 1] = 0;
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}
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sign = f.coeffs[0];
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for (i = 0; i < NTRU_N - 1; ++i) {
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r->coeffs[i] = mod3((uint8_t) (sign * v.coeffs[NTRU_N - 2 - i]));
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}
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r->coeffs[NTRU_N - 1] = 0;
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}
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