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crypto: cleaner code for Streebog carry bit handling and add comment about missing handling of overflow caused by carry bit.

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This commit is contained in:
Mounir IDRASSI 2018-08-05 16:18:23 +02:00
parent 6c9adee646
commit a11cada735
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GPG Key ID: DD0C382D5FCFB8FC
1 changed files with 24 additions and 5 deletions
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29
src/Crypto/Streebog.c
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@ -1845,21 +1845,40 @@ add512(const unsigned long long *x, const unsigned long long *y, unsigned long l
{
#ifndef __GOST3411_BIG_ENDIAN__
unsigned int CF, OF;
unsigned long long tmp;
unsigned int i;
CF = 0;
for (i = 0; i < 8; i++)
{
r[i] = x[i] + y[i];
if ( (r[i] < y[i]) ||
(r[i] < x[i]) )
/* Detecting integer overflow condition for three numbers
* in a portable way is tricky a little. */
/* Step 1: numbers cause overflow */
tmp = x[i] + y[i];
/* Compare with any of two summands, no need to check both */
if (tmp < x[i])
OF = 1;
else
OF = 0;
r[i] += CF;
/* Step 2: carry bit causes overflow */
tmp += CF;
/*
* We don't include the carry bit overflow since it can break
* mounting for some containers eventhough the probability of
* such case is very low
*/
/*
if (CF > 0 && tmp == 0)
OF = 1;
*/
CF = OF;
}
r[i] = tmp;
}
#else
const unsigned char *xp, *yp;
unsigned char *rp;