#include "tommath_private.h"

#ifdef BN_MP_MUL_2_C

/* LibTomMath, multiple-precision integer library -- Tom St Denis */

/* SPDX-License-Identifier: Unlicense */

/* b = a*2 */

mp_err mp_mul_2(const mp_int *a, mp_int *b)

{

   int     x, oldused;

   mp_err err;

   /* grow to accomodate result */

   if (b->alloc < (a->used + 1)) {

      if ((err = mp_grow(b, a->used + 1)) != MP_OKAY) {

         return err;

      }

   }

   oldused = b->used;

   b->used = a->used;

   {

      mp_digit r, rr, *tmpa, *tmpb;

      /* alias for source */

      tmpa = a->dp;

      /* alias for dest */

      tmpb = b->dp;

      /* carry */

      r = 0;

      for (x = 0; x < a->used; x++) {

         /* get what will be the *next* carry bit from the

          * MSB of the current digit

          */

         rr = *tmpa >> (mp_digit)(MP_DIGIT_BIT - 1);

         /* now shift up this digit, add in the carry [from the previous] */

         *tmpb++ = ((*tmpa++ << 1uL) | r) & MP_MASK;

         /* copy the carry that would be from the source

          * digit into the next iteration

          */

         r = rr;

      }

      /* new leading digit? */

      if (r != 0u) {

         /* add a MSB which is always 1 at this point */

         *tmpb = 1;

         ++(b->used);

      }

      /* now zero any excess digits on the destination

       * that we didn't write to

       */

      MP_ZERO_DIGITS(b->dp + b->used, oldused - b->used);

   }

   b->sign = a->sign;

   return MP_OKAY;

}

#endif