kc3-lang/libtommath/mp_mul_2.c

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• Hash : 7a68f128
  Author :
  Date : 2019-10-19T16:24:39
  

  Execute move.sh - Rename files from bn_* to match the function names. * git blame <renamed-file> is not affected * git log --follow <renamed-file> can be used to show log across renames

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• mp_mul_2.c

• #include "tommath_private.h"
  #ifdef 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
  

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