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Perf. improvement in _gej_add_ge

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- Avoid one weak normalization
- Change one full normalization to weak
- Avoid unnecessary fe assignment
- Update magnitude annotations
This commit is contained in:
Peter Dettman 2015-07-04 14:32:39 +09:30
parent 17f7148606
commit 55e7fc32cb
1 changed files with 9 additions and 11 deletions
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20
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, 5 normalize, 17 mul_int/add/negate/cmov */
/* Operations: 7 mul, 5 sqr, 4 normalize, 17 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, z, t, tt, m, n, q, rr;
secp256k1_fe_t m_alt, rr_alt;
@ -557,23 +557,21 @@ static void secp256k1_gej_add_ge(secp256k1_gej_t *r, const secp256k1_gej_t *a, c
* so M^3 * Malt is either Malt^4 (which is computed by squaring), or
* zero (which is "computed" by cmov). So the cost is one squaring
* versus two multiplications. */
secp256k1_fe_sqr(&n, &n); /* n = M^3 * Malt (1) */
secp256k1_fe_cmov(&n, &m, degenerate);
secp256k1_fe_normalize_weak(&n);
secp256k1_fe_sqr(&n, &n);
secp256k1_fe_cmov(&n, &m, degenerate); /* n = M^3 * Malt (2) */
secp256k1_fe_sqr(&t, &rr_alt); /* t = Ralt^2 (1) */
secp256k1_fe_mul(&r->z, &m_alt, &z); /* r->z = Malt*Z (1) */
infinity = secp256k1_fe_normalizes_to_zero(&r->z) * (1 - a->infinity);
secp256k1_fe_mul_int(&r->z, 2); /* r->z = Z3 = 2*Malt*Z (2) */
r->x = t; /* r->x = Ralt^2 (1) */
secp256k1_fe_negate(&q, &q, 1); /* q = -Q (2) */
secp256k1_fe_add(&r->x, &q); /* r->x = Ralt^2-Q (3) */
secp256k1_fe_normalize(&r->x);
t = r->x;
secp256k1_fe_add(&t, &q); /* t = Ralt^2-Q (3) */
secp256k1_fe_normalize_weak(&t);
r->x = t; /* r->x = Ralt^2-Q (1) */
secp256k1_fe_mul_int(&t, 2); /* t = 2*x3 (2) */
secp256k1_fe_add(&t, &q); /* t = 2*x3 - Q: (8) */
secp256k1_fe_add(&t, &q); /* t = 2*x3 - Q: (4) */
secp256k1_fe_mul(&t, &t, &rr_alt); /* t = Ralt*(2*x3 - Q) (1) */
secp256k1_fe_add(&t, &n); /* t = Ralt*(2*x3 - Q) + M^3*Malt (2) */
secp256k1_fe_negate(&r->y, &t, 2); /* r->y = Ralt*(Q - 2x3) - M^3*Malt (3) */
secp256k1_fe_add(&t, &n); /* t = Ralt*(2*x3 - Q) + M^3*Malt (3) */
secp256k1_fe_negate(&r->y, &t, 3); /* r->y = Ralt*(Q - 2x3) - M^3*Malt (4) */
secp256k1_fe_normalize_weak(&r->y);
secp256k1_fe_mul_int(&r->x, 4); /* r->x = X3 = 4*(Ralt^2-Q) */
secp256k1_fe_mul_int(&r->y, 4); /* r->y = Y3 = 4*Ralt*(Q - 2x3) - 4*M^3*Malt (4) */