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Make scalar_add_bit test's overflow detection exact

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This commit is contained in:
Pieter Wuille
2014-12-03 18:30:17 +01:00
parent d220062ac2
commit 29ae1310ce
4 changed files with 13 additions and 8 deletions
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7
src/scalar_4x64_impl.h
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@@ -81,7 +81,7 @@ SECP256K1_INLINE static int secp256k1_scalar_reduce(secp256k1_scalar_t *r, unsig
return overflow;
}
static void secp256k1_scalar_add(secp256k1_scalar_t *r, const secp256k1_scalar_t *a, const secp256k1_scalar_t *b) {
static int secp256k1_scalar_add(secp256k1_scalar_t *r, const secp256k1_scalar_t *a, const secp256k1_scalar_t *b) {
uint128_t t = (uint128_t)a->d[0] + b->d[0];
r->d[0] = t & 0xFFFFFFFFFFFFFFFFULL; t >>= 64;
t += (uint128_t)a->d[1] + b->d[1];
@@ -90,7 +90,10 @@ static void secp256k1_scalar_add(secp256k1_scalar_t *r, const secp256k1_scalar_t
r->d[2] = t & 0xFFFFFFFFFFFFFFFFULL; t >>= 64;
t += (uint128_t)a->d[3] + b->d[3];
r->d[3] = t & 0xFFFFFFFFFFFFFFFFULL; t >>= 64;
secp256k1_scalar_reduce(r, t + secp256k1_scalar_check_overflow(r));
int overflow = t + secp256k1_scalar_check_overflow(r);
VERIFY_CHECK(overflow == 0 || overflow == 1);
secp256k1_scalar_reduce(r, overflow);
return overflow;
}
static void secp256k1_scalar_add_bit(secp256k1_scalar_t *r, unsigned int bit) {