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/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
* LibTomMath is a library that provides multiple-precision
* integer arithmetic as well as number theoretic functionality.
*
* The library was 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://math.libtomcrypt.org
*/
#include <tommath.h>
/* multiply by a digit */
int
mp_mul_d (mp_int * a, mp_digit b, mp_int * c)
{
mp_digit u, *tmpa, *tmpc;
mp_word r;
int ix, res, olduse;
/* make sure c is big enough to hold a*b */
if (c->alloc < a->used + 1) {
if ((res = mp_grow (c, a->used + 1)) != MP_OKAY) {
return res;
}
}
/* get the original destinations used count */
olduse = c->used;
/* set the sign */
c->sign = a->sign;
/* alias for a->dp [source] */
tmpa = a->dp;
/* alias for c->dp [dest] */
tmpc = c->dp;
/* zero carry */
u = 0;
/* compute columns */
for (ix = 0; ix < a->used; ix++) {
/* compute product and carry sum for this term */
r = ((mp_word) u) + ((mp_word)*tmpa++) * ((mp_word)b);
/* mask off higher bits to get a single digit */
*tmpc++ = (mp_digit) (r & ((mp_word) MP_MASK));
/* send carry into next iteration */
u = (mp_digit) (r >> ((mp_word) DIGIT_BIT));
}
/* store final carry [if any] */
*tmpc++ = u;
/* now zero digits above the top */
while (ix++ < olduse) {
*tmpc++ = 0;
}
/* set used count */
c->used = a->used + 1;
mp_clamp(c);
return MP_OKAY;
}
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