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ML-KEM to bytes C: not reducing all values #9421

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Merged
dgarske merged 1 commit into from
Nov 13, 2025
Merged

ML-KEM to bytes C: not reducing all values #9421

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10 changes: 5 additions & 5 deletions wolfcrypt/src/wc_mlkem_poly.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4775,7 +4775,7 @@ static MLKEM_NOINLINE void mlkem_csubq_c(sword16* p)
for (i = 0; i < MLKEM_N; ++i) {
sword16 t = p[i] - MLKEM_Q;
/* When top bit set, -ve number - need to add q back. */
p[i] = ((t >> 15) & MLKEM_Q) + t;
p[i] = (sword16)((word16)(-((word16)t >> 15)) & MLKEM_Q) + t;
}
}

Expand Down Expand Up @@ -6021,11 +6021,11 @@ static void mlkem_to_bytes_c(byte* b, sword16* p, int k)
int i;
int j;

/* Reduce each coefficient to mod q. */
mlkem_csubq_c(p);
/* All values are now positive. */

for (j = 0; j < k; j++) {
/* Reduce each coefficient to mod q. */
mlkem_csubq_c(p);
/* All values are now positive. */

for (i = 0; i < MLKEM_N / 2; i++) {
word16 t0 = p[2 * i];
word16 t1 = p[2 * i + 1];
Expand Down