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Refactor to save a _fe_negate

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Peter Dettman 2015-07-04 16:38:46 +09:30
parent b28d02a5d5
commit 7d054cd030
1 changed files with 4 additions and 4 deletions
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8
src/group_impl.h
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@ -461,7 +461,7 @@ static void secp256k1_gej_add_zinv_var(secp256k1_gej_t *r, const secp256k1_gej_t
static void secp256k1_gej_add_ge(secp256k1_gej_t *r, const secp256k1_gej_t *a, const secp256k1_ge_t *b) {
/* Operations: 7 mul, 5 sqr, 4 normalize, 17 mul_int/add/negate/cmov */
/* Operations: 7 mul, 5 sqr, 4 normalize, 22 mul_int/add/negate/cmov */
static const secp256k1_fe_t fe_1 = SECP256K1_FE_CONST(0, 0, 0, 0, 0, 0, 0, 1);
secp256k1_fe_t zz, u1, u2, s1, s2, t, tt, m, n, q, rr;
secp256k1_fe_t m_alt, rr_alt;
@ -528,8 +528,9 @@ static void secp256k1_gej_add_ge(secp256k1_gej_t *r, const secp256k1_gej_t *a, c
t = u1; secp256k1_fe_add(&t, &u2); /* t = T = U1+U2 (2) */
m = s1; secp256k1_fe_add(&m, &s2); /* m = M = S1+S2 (2) */
secp256k1_fe_sqr(&rr, &t); /* rr = T^2 (1) */
secp256k1_fe_mul(&tt, &u1, &u2); secp256k1_fe_negate(&tt, &tt, 1); /* tt = -U1*U2 (2) */
secp256k1_fe_add(&rr, &tt); /* rr = R = T^2-U1*U2 (3) */
secp256k1_fe_negate(&m_alt, &u2, 1); /* m = -X2*Z1^2 */
secp256k1_fe_mul(&tt, &u1, &m_alt); /* tt = -U1*U2 (2) */
secp256k1_fe_add(&rr, &tt); /* rr = R = T^2-U1*U2 (3) */
/** If lambda = R/M = 0/0 we have a problem (except in the "trivial"
* case that Z = z1z2 = 0, and this is special-cased later on). */
degenerate = secp256k1_fe_normalizes_to_zero(&m) &
@ -541,7 +542,6 @@ static void secp256k1_gej_add_ge(secp256k1_gej_t *r, const secp256k1_gej_t *a, c
* so we set R/M equal to this. */
secp256k1_fe_negate(&rr_alt, &s2, 1); /* rr = -Y2*Z1^3 */
secp256k1_fe_add(&rr_alt, &s1); /* rr = Y1*Z2^3 - Y2*Z1^3 */
secp256k1_fe_negate(&m_alt, &u2, 1); /* m = -X2*Z1^2 */
secp256k1_fe_add(&m_alt, &u1); /* m = X1*Z2^2 - X2*Z1^2 */
secp256k1_fe_cmov(&rr_alt, &rr, !degenerate);