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tests: Fix test whose result is implementation-defined
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A compiler may add struct padding and fe_cmov is not guaranteed to
preserve it.

On the way, we improve the identity check such that it covers the
VERIFY struct members.
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real-or-random committed Dec 23, 2021
1 parent 09971a3 commit 3d7cbaf
Showing 1 changed file with 11 additions and 8 deletions.
19 changes: 11 additions & 8 deletions src/tests.c
Original file line number Diff line number Diff line change
Expand Up @@ -2451,13 +2451,16 @@ void run_field_convert(void) {
CHECK(secp256k1_memcmp_var(&fes2, &fes, sizeof(fes)) == 0);
}

int fe_secp256k1_memcmp_var(const secp256k1_fe *a, const secp256k1_fe *b) {
secp256k1_fe t = *b;
/* Returns true if two field elements have the same representation. */
int fe_identical(const secp256k1_fe *a, const secp256k1_fe *b) {
int ret = 1;
#ifdef VERIFY
t.magnitude = a->magnitude;
t.normalized = a->normalized;
ret &= (a->magnitude == b->magnitude);
ret &= (a->normalized == b->normalized);
#endif
return secp256k1_memcmp_var(a, &t, sizeof(secp256k1_fe));
/* Compare the struct member that holds the limbs. */
ret &= (secp256k1_memcmp_var(a->n, b->n, sizeof(a->n)) == 0);
return ret;
}

void run_field_misc(void) {
Expand All @@ -2483,13 +2486,13 @@ void run_field_misc(void) {
CHECK(x.normalized && x.magnitude == 1);
#endif
secp256k1_fe_cmov(&x, &x, 1);
CHECK(fe_secp256k1_memcmp_var(&x, &z) != 0);
CHECK(fe_secp256k1_memcmp_var(&x, &q) == 0);
CHECK(!fe_identical(&x, &z));
CHECK(fe_identical(&x, &q));
secp256k1_fe_cmov(&q, &z, 1);
#ifdef VERIFY
CHECK(!q.normalized && q.magnitude == z.magnitude);
#endif
CHECK(fe_secp256k1_memcmp_var(&q, &z) == 0);
CHECK(fe_identical(&q, &z));
secp256k1_fe_normalize_var(&x);
secp256k1_fe_normalize_var(&z);
CHECK(!secp256k1_fe_equal_var(&x, &z));
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