93 lines
2.7 KiB
C
93 lines
2.7 KiB
C
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#include "params.h"
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#include "rounding.h"
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#include <stdint.h>
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/*************************************************
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* Name: PQCLEAN_DILITHIUM5_CLEAN_power2round
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*
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* Description: For finite field element a, compute a0, a1 such that
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* a mod^+ Q = a1*2^D + a0 with -2^{D-1} < a0 <= 2^{D-1}.
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* Assumes a to be standard representative.
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*
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* Arguments: - int32_t a: input element
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* - int32_t *a0: pointer to output element a0
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*
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* Returns a1.
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**************************************************/
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int32_t PQCLEAN_DILITHIUM5_CLEAN_power2round(int32_t *a0, int32_t a) {
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int32_t a1;
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a1 = (a + (1 << (D - 1)) - 1) >> D;
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*a0 = a - (a1 << D);
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return a1;
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}
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/*************************************************
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* Name: PQCLEAN_DILITHIUM5_CLEAN_decompose
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*
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* Description: For finite field element a, compute high and low bits a0, a1 such
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* that a mod^+ Q = a1*ALPHA + a0 with -ALPHA/2 < a0 <= ALPHA/2 except
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* if a1 = (Q-1)/ALPHA where we set a1 = 0 and
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* -ALPHA/2 <= a0 = a mod^+ Q - Q < 0. Assumes a to be standard
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* representative.
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*
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* Arguments: - int32_t a: input element
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* - int32_t *a0: pointer to output element a0
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*
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* Returns a1.
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**************************************************/
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int32_t PQCLEAN_DILITHIUM5_CLEAN_decompose(int32_t *a0, int32_t a) {
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int32_t a1;
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a1 = (a + 127) >> 7;
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a1 = (a1 * 1025 + (1 << 21)) >> 22;
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a1 &= 15;
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*a0 = a - a1 * 2 * GAMMA2;
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*a0 -= (((Q - 1) / 2 - *a0) >> 31) & Q;
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return a1;
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}
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/*************************************************
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* Name: PQCLEAN_DILITHIUM5_CLEAN_make_hint
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*
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* Description: Compute hint bit indicating whether the low bits of the
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* input element overflow into the high bits.
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*
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* Arguments: - int32_t a0: low bits of input element
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* - int32_t a1: high bits of input element
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*
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* Returns 1 if overflow.
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**************************************************/
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unsigned int PQCLEAN_DILITHIUM5_CLEAN_make_hint(int32_t a0, int32_t a1) {
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if (a0 > GAMMA2 || a0 < -GAMMA2 || (a0 == -GAMMA2 && a1 != 0)) {
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return 1;
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}
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return 0;
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}
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/*************************************************
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* Name: PQCLEAN_DILITHIUM5_CLEAN_use_hint
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*
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* Description: Correct high bits according to hint.
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*
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* Arguments: - int32_t a: input element
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* - unsigned int hint: hint bit
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*
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* Returns corrected high bits.
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**************************************************/
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int32_t PQCLEAN_DILITHIUM5_CLEAN_use_hint(int32_t a, unsigned int hint) {
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int32_t a0, a1;
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a1 = PQCLEAN_DILITHIUM5_CLEAN_decompose(&a0, a);
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if (hint == 0) {
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return a1;
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}
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if (a0 > 0) {
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return (a1 + 1) & 15;
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}
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return (a1 - 1) & 15;
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}
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