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bigint.c: fix uninitialized embedded array in bint_new

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When creating a bigint with embedded storage, the array wasn't being
initialized when x->p was NULL but x->sz > 0. This could leave garbage
memory in the embedded array, which VS 2022 might interpret differently
than VS 2019, causing test failures.

This fix ensures the embedded array is always properly initialized with
zeros when x->p is NULL, preventing potential undefined behavior.

Co-authored-by: Claude <noreply@anthropic.com>
This commit is contained in:
Yukihiro "Matz" Matsumoto
2025-08-21 21:48:21 +09:00
parent fb85e8b269
commit 8fd02f28a3
1 changed files with 8 additions and 2 deletions
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mrbgems/mruby-bigint/core/bigint.c
+8 -2
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@@ -784,7 +784,7 @@ limb_addmul_1(mp_limb *rp, const mp_limb *s1p, size_t n, mp_limb limb)
return (mp_limb)acc;
#elif defined(_MSC_VER) && defined(MRB_64BIT)
#elif defined(_MSC_VER) && defined(MRB_64BIT) && !defined(MRB_NO_MPZ64BIT)
/* 64-bit limbs on MSVC with 6x unrolling: use _umul128 */
unsigned long long carry = 0;
size_t i;
@@ -2826,7 +2826,13 @@ bint_new(mpz_ctx_t *ctx, mpz_t *x)
if (x->sz <= RBIGINT_EMBED_SIZE_MAX) {
RBIGINT_SET_EMBED_SIZE(b, x->sz);
RBIGINT_SET_EMBED_SIGN(b, x->sn);
if (x->p) memcpy(RBIGINT_EMBED_ARY(b), x->p, x->sz*sizeof(mp_limb));
if (x->p) {
memcpy(RBIGINT_EMBED_ARY(b), x->p, x->sz*sizeof(mp_limb));
}
else {
/* Initialize embedded array to zero when x->p is NULL */
memset(RBIGINT_EMBED_ARY(b), 0, x->sz*sizeof(mp_limb));
}
mpz_clear(ctx, x);
}
else {