#include "tommath_private.h"
#ifdef 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;
mp_err err;
int ix, oldused;
if (b == 1u) {
return mp_copy(a, c);
}
/* power of two ? */
if (MP_HAS(MP_MUL_2) && (b == 2u)) {
return mp_mul_2(a, c);
}
if (MP_HAS(MP_MUL_2D) && MP_IS_2EXPT(b)) {
ix = 1;
while ((ix < MP_DIGIT_BIT) && (b != (((mp_digit)1)<<ix))) {
ix++;
}
return mp_mul_2d(a, ix, c);
}
/* make sure c is big enough to hold a*b */
if ((err = mp_grow(c, a->used + 1)) != MP_OKAY) {
return err;
}
/* get the original destinations used count */
oldused = c->used;
/* set the sign */
c->sign = a->sign;
/* zero carry */
u = 0;
/* compute columns */
for (ix = 0; ix < a->used; ix++) {
/* compute product and carry sum for this term */
mp_word r = (mp_word)u + ((mp_word)a->dp[ix] * (mp_word)b);
/* mask off higher bits to get a single digit */
c->dp[ix] = (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 */
c->dp[ix] = u;
/* set used count */
c->used = a->used + 1;
/* now zero digits above the top */
s_mp_zero_digs(c->dp + c->used, oldused - c->used);
mp_clamp(c);
return MP_OKAY;
}
#endif
