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Make secp256k1_scalar_get_bits support 32-bit reads

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The old code would trigger UB when count=32.
This commit is contained in:
Pieter Wuille
2021-12-28 18:13:04 -05:00
parent 5005abee60
commit e03dcc44b5
4 changed files with 15 additions and 11 deletions
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8
src/scalar_low_impl.h
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@@ -30,10 +30,12 @@ SECP256K1_INLINE static void secp256k1_scalar_set_int(secp256k1_scalar *r, unsig
SECP256K1_INLINE static uint32_t secp256k1_scalar_get_bits_limb32(const secp256k1_scalar *a, unsigned int offset, unsigned int count) {
SECP256K1_SCALAR_VERIFY(a);
if (offset < 32)
return ((*a >> offset) & ((((uint32_t)1) << count) - 1));
else
VERIFY_CHECK(count > 0 && count <= 32);
if (offset < 32) {
return (*a >> offset) & (0xFFFFFFFF >> (32 - count));
} else {
return 0;
}
}
SECP256K1_INLINE static uint32_t secp256k1_scalar_get_bits_var(const secp256k1_scalar *a, unsigned int offset, unsigned int count) {