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Make secp256k1_modinv64_det_check_pow2 support abs val

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This commit is contained in:
Pieter Wuille 2022-12-10 15:22:32 -05:00
parent 5fffb2c7af
commit 04c6c1b181
1 changed files with 7 additions and 5 deletions
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12
src/modinv64_impl.h
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@ -71,11 +71,13 @@ static int secp256k1_modinv64_mul_cmp_62(const secp256k1_modinv64_signed62 *a, i
return 0;
}
/* Check if the determinant of t is equal to 1 << n. */
static int secp256k1_modinv64_det_check_pow2(const secp256k1_modinv64_trans2x2 *t, unsigned int n) {
/* Check if the determinant of t is equal to 1 << n. If abs, check if |det t| == 1 << n. */
static int secp256k1_modinv64_det_check_pow2(const secp256k1_modinv64_trans2x2 *t, unsigned int n, int abs) {
secp256k1_int128 a;
secp256k1_i128_det(&a, t->u, t->v, t->q, t->r);
return secp256k1_i128_check_pow2(&a, n, 1);
if (secp256k1_i128_check_pow2(&a, n, 1)) return 1;
if (abs && secp256k1_i128_check_pow2(&a, n, -1)) return 1;
return 0;
}
#endif
@ -218,7 +220,7 @@ static int64_t secp256k1_modinv64_divsteps_59(int64_t zeta, uint64_t f0, uint64_
* aggregate of 59 of them will have determinant 2^59. Multiplying with the initial
* 8*identity (which has determinant 2^6) means the overall outputs has determinant
* 2^65. */
VERIFY_CHECK(secp256k1_modinv64_det_check_pow2(t, 65));
VERIFY_CHECK(secp256k1_modinv64_det_check_pow2(t, 65, 0));
#endif
return zeta;
}
@ -301,7 +303,7 @@ static int64_t secp256k1_modinv64_divsteps_62_var(int64_t eta, uint64_t f0, uint
* does not change the gcd of f and g, apart from adding a power-of-2 factor to it (which
* will be divided out again). As each divstep's individual matrix has determinant 2, the
* aggregate of 62 of them will have determinant 2^62. */
VERIFY_CHECK(secp256k1_modinv64_det_check_pow2(t, 62));
VERIFY_CHECK(secp256k1_modinv64_det_check_pow2(t, 62, 0));
#endif
return eta;
}