45 lines
1.3 KiB
C
45 lines
1.3 KiB
C
#include "parameters.h"
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#include "repetition.h"
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#include <immintrin.h>
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#include <stddef.h>
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#include <stdint.h>
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#include <stdio.h>
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/**
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* @file repetition.c
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* @brief Implementation of repetition codes
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*/
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/**
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* @brief Decoding the code words to a message using the repetition code
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*
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* We use a majority decoding. In fact we have that PARAM_N2 = 2 * PARAM_T + 1, thus,
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* if the Hamming weight of the vector is greater than PARAM_T, the code word is decoded
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* to 1 and 0 otherwise.
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*
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* @param[out] m Pointer to an array that is the message
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* @param[in] em Pointer to an array that is the code word
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*/
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void PQCLEAN_HQC256_AVX2_repetition_code_decode(uint64_t *m, const uint64_t *em) {
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uint32_t t = 0;
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uint32_t b, bn, bi, c, cn, ci;
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uint64_t cx, ones;
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uint64_t cy;
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uint64_t mask;
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for (b = 0; b < PARAM_N1N2 - PARAM_N2 + 1; b += PARAM_N2) {
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bn = b >> 6;
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bi = b & 63;
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c = b + PARAM_N2 - 1;
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cn = c >> 6;
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ci = c & 63;
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cx = em[cn] << (63 - ci);
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mask = (uint64_t) (-((int64_t) (cn ^ (bn + 1))) >> 63); // cn != bn+1
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cy = em[bn + 1];
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ones = _mm_popcnt_u64((em[bn] >> bi) | (cx & mask)) + _mm_popcnt_u64((mask & cy) + (~mask & cx));
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m[t >> 6] |= (uint64_t) (((((int64_t)PARAM_T - ones) >> 63) & 1) << (t & 63)); // 1 << (t&63) if ones > PARAM_T else 0
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t++;
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}
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}
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