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shallue_van_de_woestijne support for t = 0 #284

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shallue_van_de_woestijne support for t = 0 #284

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6 changes: 5 additions & 1 deletion src/modules/generator/main_impl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -90,6 +90,7 @@ int secp256k1_generator_serialize(const secp256k1_context* ctx, unsigned char *o
return 1;
}

/* t must be normalized. */
static void shallue_van_de_woestijne(secp256k1_ge* ge, const secp256k1_fe* t) {
/* Implements the algorithm from:
* Indifferentiable Hashing to Barreto-Naehrig Curves
Expand Down Expand Up @@ -128,7 +129,7 @@ static void shallue_van_de_woestijne(secp256k1_ge* ge, const secp256k1_fe* t) {
static const secp256k1_fe b_plus_one = SECP256K1_FE_CONST(0, 0, 0, 0, 0, 0, 0, 8);

secp256k1_fe wn, wd, x1n, x2n, x3n, x3d, jinv, tmp, x1, x2, x3, alphain, betain, gammain, y1, y2, y3;
int alphaquad, betaquad;
int alphaquad, betaquad, zerot;

secp256k1_fe_mul(&wn, &c, t); /* mag 1 */
secp256k1_fe_sqr(&wd, t); /* mag 1 */
Expand All @@ -153,6 +154,9 @@ static void shallue_van_de_woestijne(secp256k1_ge* ge, const secp256k1_fe* t) {
secp256k1_fe_mul(&x3, &x3n, &wd); /* mag 1 */
secp256k1_fe_mul(&x3, &x3, &jinv); /* mag 1 */

zerot = secp256k1_fe_is_zero(t);
secp256k1_fe_cmov(&x1, &d, zerot);

secp256k1_fe_sqr(&alphain, &x1); /* mag 1 */
secp256k1_fe_mul(&alphain, &alphain, &x1); /* mag 1 */
secp256k1_fe_add(&alphain, &b); /* mag 2 */
Expand Down