mirror of
https://github.com/henrydcase/pqc.git
synced 2024-12-04 21:34:01 +00:00
120 lines
3.3 KiB
C
120 lines
3.3 KiB
C
#include "params.h"
|
|
#include <stdint.h>
|
|
|
|
/*************************************************
|
|
* Name: power2round
|
|
*
|
|
* Description: For finite field element a, compute a0, a1 such that
|
|
* a mod Q = a1*2^D + a0 with -2^{D-1} < a0 <= 2^{D-1}.
|
|
* Assumes a to be standard representative.
|
|
*
|
|
* Arguments: - uint32_t a: input element
|
|
* - uint32_t *a0: pointer to output element Q + a0
|
|
*
|
|
* Returns a1.
|
|
**************************************************/
|
|
uint32_t PQCLEAN_DILITHIUMIII_CLEAN_power2round(uint32_t a, uint32_t *a0) {
|
|
int32_t t;
|
|
|
|
/* Centralized remainder mod 2^D */
|
|
t = a & ((1 << D) - 1);
|
|
t -= (1 << (D - 1)) + 1;
|
|
t += (t >> 31) & (1 << D);
|
|
t -= (1 << (D - 1)) - 1;
|
|
*a0 = Q + t;
|
|
a = (a - t) >> D;
|
|
return a;
|
|
}
|
|
|
|
/*************************************************
|
|
* Name: decompose
|
|
*
|
|
* Description: For finite field element a, compute high and low bits a0, a1
|
|
*such that a mod Q = a1*ALPHA + a0 with -ALPHA/2 < a0 <= ALPHA/2 except if a1 =
|
|
*(Q-1)/ALPHA where we set a1 = 0 and -ALPHA/2 <= a0 = a mod Q - Q < 0. Assumes
|
|
*a to be standard representative.
|
|
*
|
|
* Arguments: - uint32_t a: input element
|
|
* - uint32_t *a0: pointer to output element Q + a0
|
|
*
|
|
* Returns a1.
|
|
**************************************************/
|
|
uint32_t PQCLEAN_DILITHIUMIII_CLEAN_decompose(uint32_t a, uint32_t *a0) {
|
|
#if ALPHA != (Q - 1) / 16
|
|
#error "decompose assumes ALPHA == (Q-1)/16"
|
|
#endif
|
|
int32_t t, u;
|
|
|
|
/* Centralized remainder mod ALPHA */
|
|
t = a & 0x7FFFF;
|
|
t += (a >> 19) << 9;
|
|
t -= ALPHA / 2 + 1;
|
|
t += (t >> 31) & ALPHA;
|
|
t -= ALPHA / 2 - 1;
|
|
a -= t;
|
|
|
|
/* Divide by ALPHA (possible to avoid) */
|
|
u = a - 1;
|
|
u >>= 31;
|
|
a = (a >> 19) + 1;
|
|
a -= u & 1;
|
|
|
|
/* Border case */
|
|
*a0 = Q + t - (a >> 4);
|
|
a &= 0xF;
|
|
return a;
|
|
}
|
|
|
|
/*************************************************
|
|
* Name: make_hint
|
|
*
|
|
* Description: Compute hint bit indicating whether or not high bits of two
|
|
* finite field elements differ. Assumes input elements to be
|
|
* standard representatives.
|
|
*
|
|
* Arguments: - uint32_t a: first input element
|
|
* - uint32_t b: second input element
|
|
*
|
|
* Returns 1 if high bits of a and b differ and 0 otherwise.
|
|
**************************************************/
|
|
unsigned int PQCLEAN_DILITHIUMIII_CLEAN_make_hint(const uint32_t a,
|
|
const uint32_t b) {
|
|
uint32_t t;
|
|
|
|
return PQCLEAN_DILITHIUMIII_CLEAN_decompose(a, &t) !=
|
|
PQCLEAN_DILITHIUMIII_CLEAN_decompose(b, &t);
|
|
}
|
|
|
|
/*************************************************
|
|
* Name: use_hint
|
|
*
|
|
* Description: Correct high bits according to hint.
|
|
*
|
|
* Arguments: - uint32_t a: input element
|
|
* - unsigned int hint: hint bit
|
|
*
|
|
* Returns corrected high bits.
|
|
**************************************************/
|
|
uint32_t PQCLEAN_DILITHIUMIII_CLEAN_use_hint(const uint32_t a,
|
|
const unsigned int hint) {
|
|
uint32_t a0, a1;
|
|
|
|
a1 = PQCLEAN_DILITHIUMIII_CLEAN_decompose(a, &a0);
|
|
if (hint == 0) {
|
|
return a1;
|
|
}
|
|
if (a0 > Q) {
|
|
return (a1 + 1) & 0xF;
|
|
}
|
|
return (a1 - 1) & 0xF;
|
|
|
|
/* If decompose does not divide out ALPHA:
|
|
if(hint == 0)
|
|
return a1;
|
|
else if(a0 > Q)
|
|
return (a1 + ALPHA) % (Q - 1);
|
|
else
|
|
return (a1 - ALPHA) % (Q - 1);
|
|
*/
|
|
}
|