Differential D7595 Diff 23856 src/secp256k1/src/ecmult_const_impl.h

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src/secp256k1/src/ecmult_const_impl.h

Show First 20 Lines • Show All 95 Lines • ▼ Show 20 Lines	static int secp256k1_wnaf_const(int wnaf, const secp256k1_scalar scalar, int w, int size) {
* 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);
do {		do {
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;		/* In contrast to the original algorithm, u_last is always > 0 and
u += sign * even;		* therefore we do not need to check its sign. In particular, it's easy
u_last -= sign * even * (1 << w);		* to see that u_last is never < 0 because u is never < 0. Moreover,
		* u_last is never = 0 because u is never even after a loop
		* iteration. The same holds analogously for the initial value of
		* u_last (in the first loop iteration). */
		VERIFY_CHECK(u_last > 0);
		VERIFY_CHECK((u_last & 1) == 1);
		u += even;
		u_last -= 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);		} while (word * w < size);
wnaf[word] = u * global_sign;		wnaf[word] = u * global_sign;

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