Differential D4995 Diff 15605 src/secp256k1/src/ecmult_const_impl.h

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src/secp256k1/src/ecmult_const_impl.h

Show First 20 Lines • Show All 55 Lines • ▼ Show 20 Lines	static int secp256k1_wnaf_const(int wnaf, const secp256k1_scalar scalar, int w, int size) {
/* 1 2 3 */		/* 1 2 3 */
int u_last;		int u_last;
int u;		int u;

int flip;		int flip;
int bit;		int bit;
secp256k1_scalar s;		secp256k1_scalar s;
int not_neg_one;		int not_neg_one;

		VERIFY_CHECK(w > 0);
		VERIFY_CHECK(size > 0);

/* Note that we cannot handle even numbers by negating them to be odd, as is		/* Note that we cannot handle even numbers by negating them to be odd, as is
* done in other implementations, since if our scalars were specified to have		* done in other implementations, since if our scalars were specified to have
* width < 256 for performance reasons, their negations would have width 256		* width < 256 for performance reasons, their negations would have width 256
* and we'd lose any performance benefit. Instead, we use a technique from		* and we'd lose any performance benefit. Instead, we use a technique from
* Section 4.2 of the Okeya/Tagaki paper, which is to add either 1 (for even)		* Section 4.2 of the Okeya/Tagaki paper, which is to add either 1 (for even)
* or 2 (for odd) to the number we are encoding, returning a skew value indicating		* or 2 (for odd) to the number we are encoding, returning a skew value indicating
* this, and having the caller compensate after doing the multiplication.		* this, and having the caller compensate after doing the multiplication.
*		*
Show All 17 Lines	static int secp256k1_wnaf_const(int wnaf, const secp256k1_scalar scalar, int w, int size) {
* the skew must be 1 or 2, never zero) and flipping is not, we need to change		* the skew must be 1 or 2, never zero) and flipping is not, we need to change
* our flags to claim that we only skewed. */		* our flags to claim that we only skewed. */
global_sign = secp256k1_scalar_cond_negate(&s, flip);		global_sign = secp256k1_scalar_cond_negate(&s, flip);
global_sign = not_neg_one 2 - 1;		global_sign = not_neg_one 2 - 1;
skew = 1 << bit;		skew = 1 << bit;

/* 4 */		/* 4 */
u_last = secp256k1_scalar_shr_int(&s, w);		u_last = secp256k1_scalar_shr_int(&s, w);
while (word * w < size) {		do {
int sign;		int sign;
int even;		int even;

/* 4.1 4.4 */		/* 4.1 4.4 */
u = secp256k1_scalar_shr_int(&s, w);		u = secp256k1_scalar_shr_int(&s, w);
/* 4.2 */		/* 4.2 */
even = ((u & 1) == 0);		even = ((u & 1) == 0);
sign = 2 * (u_last > 0) - 1;		sign = 2 * (u_last > 0) - 1;
u += sign * even;		u += sign * even;
u_last -= sign * even * (1 << w);		u_last -= sign * even * (1 << w);

/* 4.3, adapted for global sign change */		/* 4.3, adapted for global sign change */
wnaf[word++] = u_last * global_sign;		wnaf[word++] = u_last * global_sign;

u_last = u;		u_last = u;
}		} while (word * w < size);
wnaf[word] = u * global_sign;		wnaf[word] = u * global_sign;

VERIFY_CHECK(secp256k1_scalar_is_zero(&s));		VERIFY_CHECK(secp256k1_scalar_is_zero(&s));
VERIFY_CHECK(word == WNAF_SIZE_BITS(size, w));		VERIFY_CHECK(word == WNAF_SIZE_BITS(size, w));
return skew;		return skew;
}		}

static void secp256k1_ecmult_const(secp256k1_gej r, const secp256k1_ge a, const secp256k1_scalar *scalar, int size) {		static void secp256k1_ecmult_const(secp256k1_gej r, const secp256k1_ge a, const secp256k1_scalar *scalar, int size) {
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