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libmp: timingsafe sign flip for small power-of-two negative divisor for mpdiv()

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This commit is contained in:
cinap_lenrek 2016-08-28 16:33:52 +02:00
parent b65f409d54
commit bdc87e17bd
1 changed files with 2 additions and 3 deletions
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5
sys/src/libmp/port/mpdiv.c
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@ -24,12 +24,11 @@ mpdiv(mpint *dividend, mpint *divisor, mpint *quotient, mpint *remainder)
if(divisor->top == 1 && (divisor->p[0] & divisor->p[0]-1) == 0){
vlong r = (vlong)dividend->sign * (dividend->p[0] & divisor->p[0]-1);
if(quotient != nil){
sign = divisor->sign;
for(s = 0; ((divisor->p[0] >> s) & 1) == 0; s++)
;
mpright(dividend, s, quotient);
if(sign < 0 && quotient->top != 0)
quotient->sign ^= -2;
if(divisor->sign < 0)
quotient->sign ^= (-mpmagcmp(quotient, mpzero) >> 31) << 1;
}
if(remainder != nil){
remainder->flags |= dividend->flags & MPtimesafe;