From 7d054cd030ab81d484ef8f98efdbd34e2e1781b5 Mon Sep 17 00:00:00 2001 From: Peter Dettman Date: Sat, 4 Jul 2015 16:38:46 +0930 Subject: [PATCH] Refactor to save a _fe_negate --- src/group_impl.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/src/group_impl.h b/src/group_impl.h index 589f33728e744..f2268f9e548a8 100644 --- a/src/group_impl.h +++ b/src/group_impl.h @@ -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);