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pqcrypto/crypto_kem/hqc-192/avx2/repetition.c
2021-03-24 21:02:47 +00:00

42 lines
1.2 KiB
C

#include "parameters.h"
#include "repetition.h"
#include <immintrin.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
/**
* @file repetition.c
* @brief Implementation of repetition codes
*/
#define MASK_N2 ((((uint64_t) 1) << PARAM_N2) - 1)
/**
* @brief Decoding the code words to a message using the repetition code
*
* We use a majority decoding. In fact we have that PARAM_N2 = 2 * PARAM_T + 1, thus,
* if the Hamming weight of the vector is greater than PARAM_T, the code word is decoded
* to 1 and 0 otherwise.
*
* @param[out] m Pointer to an array that is the message
* @param[in] em Pointer to an array that is the code word
*/
void PQCLEAN_HQC192_AVX2_repetition_code_decode(uint64_t *m, const uint64_t *em) {
size_t t = 0, b, bn, bi, c, cn, ci;
uint64_t cx, ones;
for (b = 0 ; b < PARAM_N1N2 - PARAM_N2 + 1 ; b += PARAM_N2) {
bn = b >> 6;
bi = b & 63;
c = b + PARAM_N2 - 1;
cn = c >> 6;
ci = c & 63;
cx = em[cn] << (63 - ci);
int64_t verif = (cn == (bn + 1));
ones = _mm_popcnt_u64(((em[bn] >> bi) & MASK_N2) | (cx * verif));
m[t >> 6] |= ((uint64_t)(ones > PARAM_T)) << (t & 63);
t++;
}
}