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#include <stdint.h>
#include "kyber512r3_params.h"
#include "kyber512r3_cbd.h"
/*************************************************
* Name: load32_littleendian
*
* Description: load 4 bytes into a 32-bit integer
* in little-endian order
*
* Arguments: - const uint8_t *x: pointer to input byte array
*
* Returns 32-bit unsigned integer loaded from x
**************************************************/
static uint32_t load32_littleendian(const uint8_t x[4]) {
uint32_t r;
r = (uint32_t)x[0];
r |= (uint32_t)x[1] << 8;
r |= (uint32_t)x[2] << 16;
r |= (uint32_t)x[3] << 24;
return r;
}
/*************************************************
* Name: load24_littleendian
*
* Description: load 3 bytes into a 32-bit integer
* in little-endian order
* This function is only needed for Kyber-512
*
* Arguments: - const uint8_t *x: pointer to input byte array
*
* Returns 32-bit unsigned integer loaded from x (most significant byte is zero)
**************************************************/
static uint32_t load24_littleendian(const uint8_t x[3]) {
uint32_t r;
r = (uint32_t)x[0];
r |= (uint32_t)x[1] << 8;
r |= (uint32_t)x[2] << 16;
return r;
}
/*************************************************
* Name: cbd2
*
* Description: Given an array of uniformly random bytes, compute
* polynomial with coefficients distributed according to
* a centered binomial distribution with parameter eta=2
*
* Arguments: - poly *r: pointer to output polynomial
* - const uint8_t *buf: pointer to input byte array
**************************************************/
static void cbd2(poly *r, const uint8_t buf[2 * S2N_KYBER_512_R3_N / 4]) {
unsigned int i, j;
for (i = 0; i < S2N_KYBER_512_R3_N / 8; i++) {
uint32_t t = load32_littleendian(buf + 4 * i);
uint32_t d = t & 0x55555555;
d += (t >> 1) & 0x55555555;
for (j = 0; j < 8; j++) {
int16_t a = (d >> (4 * j + 0)) & 0x3;
int16_t b = (d >> (4 * j + 2)) & 0x3;
r->coeffs[8 * i + j] = a - b;
}
}
}
/*************************************************
* Name: cbd3
*
* Description: Given an array of uniformly random bytes, compute
* polynomial with coefficients distributed according to
* a centered binomial distribution with parameter eta=3
* This function is only needed for Kyber-512
*
* Arguments: - poly *r: pointer to output polynomial
* - const uint8_t *buf: pointer to input byte array
**************************************************/
static void cbd3(poly *r, const uint8_t buf[3 * S2N_KYBER_512_R3_N / 4]) {
unsigned int i, j;
for (i = 0; i < S2N_KYBER_512_R3_N / 4; i++) {
uint32_t t = load24_littleendian(buf + 3 * i);
uint32_t d = t & 0x00249249;
d += (t >> 1) & 0x00249249;
d += (t >> 2) & 0x00249249;
for (j = 0; j < 4; j++) {
int16_t a = (d >> (6 * j + 0)) & 0x7;
int16_t b = (d >> (6 * j + 3)) & 0x7;
r->coeffs[4 * i + j] = a - b;
}
}
}
void cbd_eta1(poly *r, const uint8_t buf[S2N_KYBER_512_R3_ETA1 * S2N_KYBER_512_R3_N / 4]) {
cbd3(r, buf);
}
void cbd_eta2(poly *r, const uint8_t buf[S2N_KYBER_512_R3_ETA2 * S2N_KYBER_512_R3_N / 4]) {
cbd2(r, buf);
}
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