62 lines
1.4 KiB
C
62 lines
1.4 KiB
C
#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 */
|
|
mp_err mp_mul_d(const mp_int *a, mp_digit b, mp_int *c)
|
|
{
|
|
mp_digit u, *tmpa, *tmpc;
|
|
mp_word r;
|
|
mp_err err;
|
|
int ix, olduse;
|
|
|
|
/* make sure c is big enough to hold a*b */
|
|
if (c->alloc < (a->used + 1)) {
|
|
if ((err = mp_grow(c, a->used + 1)) != MP_OKAY) {
|
|
return err;
|
|
}
|
|
}
|
|
|
|
/* 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)MP_DIGIT_BIT);
|
|
}
|
|
|
|
/* store final carry [if any] and increment ix offset */
|
|
*tmpc++ = u;
|
|
++ix;
|
|
|
|
/* now zero digits above the top */
|
|
MP_ZERO_DIGITS(tmpc, olduse - ix);
|
|
|
|
/* set used count */
|
|
c->used = a->used + 1;
|
|
mp_clamp(c);
|
|
|
|
return MP_OKAY;
|
|
}
|
|
#endif
|