#include "tommath_private.h"
#ifdef BN_MP_MUL_D_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */
/* multiply by a digit */
int mp_mul_d(const 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] and increment ix offset */
*tmpc++ = u;
++ix;
/* 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;
}
#endif
