mirror of
https://github.com/henrydcase/pqc.git
synced 2024-11-23 07:59:01 +00:00
71 lines
2.0 KiB
C
71 lines
2.0 KiB
C
#include "reduce.h"
|
|
#include "params.h"
|
|
|
|
static const uint32_t qinv = 7679; // -inverse_mod(q,2^18)
|
|
static const uint32_t rlog = 18;
|
|
|
|
/*************************************************
|
|
* Name: montgomery_reduce
|
|
*
|
|
* Description: Montgomery reduction; given a 32-bit integer a, computes
|
|
* 16-bit integer congruent to a * R^-1 mod q,
|
|
* where R=2^18 (see value of rlog)
|
|
*
|
|
* Arguments: - uint32_t a: input unsigned integer to be reduced; has to be in
|
|
*{0,...,2281446912}
|
|
*
|
|
* Returns: unsigned integer in {0,...,2^13-1} congruent to a * R^-1 modulo
|
|
*q.
|
|
**************************************************/
|
|
uint16_t PQCLEAN_KYBER768_montgomery_reduce(uint32_t a) {
|
|
uint32_t u;
|
|
|
|
u = (a * qinv);
|
|
u &= ((1 << rlog) - 1);
|
|
u *= KYBER_Q;
|
|
a = a + u;
|
|
return a >> rlog;
|
|
}
|
|
|
|
/*************************************************
|
|
* Name: barrett_reduce
|
|
*
|
|
* Description: Barrett reduction; given a 16-bit integer a, computes
|
|
* 16-bit integer congruent to a mod q in {0,...,11768}
|
|
*
|
|
* Arguments: - uint16_t a: input unsigned integer to be reduced
|
|
*
|
|
* Returns: unsigned integer in {0,...,11768} congruent to a modulo q.
|
|
**************************************************/
|
|
uint16_t PQCLEAN_KYBER768_barrett_reduce(uint16_t a) {
|
|
uint32_t u;
|
|
|
|
u = a >> 13; //((uint32_t) a * sinv) >> 16;
|
|
u *= KYBER_Q;
|
|
a -= u;
|
|
return a;
|
|
}
|
|
|
|
/*************************************************
|
|
* Name: freeze
|
|
*
|
|
* Description: Full reduction; given a 16-bit integer a, computes
|
|
* unsigned integer a mod q.
|
|
*
|
|
* Arguments: - uint16_t x: input unsigned integer to be reduced
|
|
*
|
|
* Returns: unsigned integer in {0,...,q-1} congruent to a modulo q.
|
|
**************************************************/
|
|
uint16_t PQCLEAN_KYBER768_freeze(uint16_t x) {
|
|
uint16_t m, r;
|
|
int16_t c;
|
|
r = PQCLEAN_KYBER768_barrett_reduce(x);
|
|
|
|
m = r - KYBER_Q;
|
|
c = m;
|
|
c >>= 15;
|
|
r = m ^ ((r ^ m) & c);
|
|
|
|
return r;
|
|
}
|