mirror of
https://github.com/henrydcase/pqc.git
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53 lines
1.5 KiB
C
53 lines
1.5 KiB
C
#include "cbd.h"
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#include "params.h"
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#include <stddef.h>
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#include <stdint.h>
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/*************************************************
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* Name: load32_littleendian
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*
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* Description: load bytes into a 32-bit integer
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* in little-endian order
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*
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* Arguments: - const uint8_t *x: pointer to input byte array
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*
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* Returns 32-bit unsigned integer loaded from x
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**************************************************/
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static uint32_t load32_littleendian(const uint8_t *x) {
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uint32_t r;
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r = (uint32_t)x[0];
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r |= (uint32_t)x[1] << 8;
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r |= (uint32_t)x[2] << 16;
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r |= (uint32_t)x[3] << 24;
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return r;
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}
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/*************************************************
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* Name: cbd
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*
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* Description: Given an array of uniformly random bytes, compute
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* polynomial with coefficients distributed according to
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* a centered binomial distribution with parameter KYBER_ETA
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* specialized for KYBER_ETA=2
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*
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* Arguments: - poly *r: pointer to output polynomial
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* - const uint8_t *buf: pointer to input byte array
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**************************************************/
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void PQCLEAN_KYBER51290S_CLEAN_cbd(poly *r, const uint8_t *buf) {
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uint32_t d, t;
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int16_t a, b;
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for (size_t i = 0; i < KYBER_N / 8; i++) {
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t = load32_littleendian(buf + 4 * i);
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d = t & 0x55555555;
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d += (t >> 1) & 0x55555555;
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for (size_t j = 0; j < 8; j++) {
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a = (d >> 4 * j) & 0x3;
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b = (d >> (4 * j + 2)) & 0x3;
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r->coeffs[8 * i + j] = a - b;
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}
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}
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}
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