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bn/bn_lib.c address Coverity nit in bn2binpad.

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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.

Reviewed-by: Rich Salz <rsalz@openssl.org>
This commit is contained in:
Andy Polyakov 2018-07-16 18:17:44 +02:00
parent 9e6a32025e
commit 83e034379f
1 changed files with 11 additions and 12 deletions
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23
crypto/bn/bn_lib.c
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@ -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;