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Merge #644: Avoid optimizing out a verify_check

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94ae7cb Moved a dereference so the null check will be before the dereferencing (Elichai Turkel)

Pull request description:

  Before that even on debug the compiler could've assumed `a` isn't null and optimized `VERIFY_CHECK(a != NULL);` out.
  This put the dereference after the check
  Resolves #643

ACKs for commit 94ae7c:
  sipa:
    ACK 94ae7cbf83a34456e5cad721f61ea77fcc023a3f

Tree-SHA512: 8b986f202ede5bde1f14a8ecf25e339d64ee6cd5cb391c5f18b4ff58f946c3845902d1230bc80d110a0a33b37025d281bd4532afbdf03b1c9ca321097374eb8e
This commit is contained in:
Pieter Wuille 2019-08-06 15:28:48 -07:00
commit e95f8ab098
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GPG Key ID: A636E97631F767E0
1 changed files with 2 additions and 1 deletions
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src/ecmult_impl.h
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@ -395,7 +395,7 @@ static void secp256k1_ecmult_context_clear(secp256k1_ecmult_context *ctx) {
* than the number of bits in the (absolute value) of the input.
*/
static int secp256k1_ecmult_wnaf(int *wnaf, int len, const secp256k1_scalar *a, int w) {
secp256k1_scalar s = *a;
secp256k1_scalar s;
int last_set_bit = -1;
int bit = 0;
int sign = 1;
@ -408,6 +408,7 @@ static int secp256k1_ecmult_wnaf(int *wnaf, int len, const secp256k1_scalar *a,
memset(wnaf, 0, len * sizeof(wnaf[0]));
s = *a;
if (secp256k1_scalar_get_bits(&s, 255, 1)) {
secp256k1_scalar_negate(&s, &s);
sign = -1;