#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