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/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
* LibTomMath is library that provides for multiple-precision
* integer arithmetic as well as number theoretic functionality.
*
* The library is designed directly after the MPI library by
* Michael Fromberger but has been written from scratch with
* additional optimizations in place.
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, tomstdenis@iahu.ca, http://libtommath.iahu.ca
*/
#include <tommath.h>
/* b = a*2 */
int
mp_mul_2 (mp_int * a, mp_int * b)
{
int x, res, oldused;
/* Optimization: should copy and shift at the same time */
if (b->alloc < a->used) {
if ((res = mp_grow (b, a->used)) != MP_OKAY) {
return res;
}
}
oldused = b->used;
b->used = a->used;
/* shift any bit count < DIGIT_BIT */
{
register mp_digit r, rr, *tmpa, *tmpb;
r = 0;
tmpa = a->dp;
tmpb = b->dp;
for (x = 0; x < b->used; x++) {
rr = *tmpa >> (DIGIT_BIT - 1);
*tmpb++ = ((*tmpa++ << 1) | r) & MP_MASK;
r = rr;
}
/* new leading digit? */
if (r != 0) {
if (b->alloc == b->used) {
if ((res = mp_grow (b, b->used + 1)) != MP_OKAY) {
return res;
}
}
/* add a MSB of 1 */
*tmpb = 1;
++b->used;
}
tmpb = b->dp + b->used;
for (x = b->used; x < oldused; x++) {
*tmpb++ = 0;
}
}
return MP_OKAY;
}
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