bn/bn_lib.c address Coverity nit in bn2binpad.
It was false positive, but one can as well view it as readability issue.
Switch even to unsigned indices because % BN_BYTES takes 4-6 instructions
with signed dividend vs. 1 (one) with unsigned.
@@ -417,28 +417,27 @@ BIGNUM *BN_bin2bn(const unsigned char *s, int len, BIGNUM *ret)
/* ignore negative */
static int bn2binpad(const BIGNUM *a, unsigned char *to, int tolen)
{
- int i, j, top;
+ int n;
+ size_t i, inc, lasti, j;
BN_ULONG l;
- i = BN_num_bytes(a);
+ n = BN_num_bytes(a);
if (tolen == -1)
- tolen = i;
- else if (tolen < i)
+ tolen = n;
+ else if (tolen < n)
return -1;
- if (i == 0) {
+ if (n == 0) {
OPENSSL_cleanse(to, tolen);
return tolen;
}
- top = a->top * BN_BYTES;
- for (i = 0, j = tolen; j > 0; i++) {
- unsigned int mask;
-
- mask = constant_time_lt(i, top);
- i -= 1 & ~mask; /* stay on top limb */
+ lasti = n - 1;
+ for (i = 0, inc = 1, j = tolen; j > 0;) {
l = a->d[i / BN_BYTES];
- to[--j] = (unsigned char)(l >> (8 * (i % BN_BYTES)) & mask);
+ to[--j] = (unsigned char)(l >> (8 * (i % BN_BYTES)) & (0 - inc));
+ inc = (i - lasti) >> (8 * sizeof(i) - 1);
+ i += inc; /* stay on top limb */
}
return tolen;
