kc3-lang/libtommath/mp_mul_2.c

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• Hash : c7686f24
  Author :
  Date : 2022-10-02T12:58:53
  

  slightly edit, update and run typos.sh Signed-off-by: Steffen Jaeckel <s@jaeckel.eu>

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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)
  {
     mp_err err;
     int x, oldused;
     mp_digit r;
  
     /* grow to accommodate result */
     if ((err = mp_grow(b, a->used + 1)) != MP_OKAY) {
        return err;
     }
  
     oldused = b->used;
     b->used = a->used;
  
     /* 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
         */
        mp_digit rr = a->dp[x] >> (mp_digit)(MP_DIGIT_BIT - 1);
  
        /* now shift up this digit, add in the carry [from the previous] */
        b->dp[x] = ((a->dp[x] << 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 */
        b->dp[b->used++] = 1;
     }
  
     /* now zero any excess digits on the destination
      * that we didn't write to
      */
     s_mp_zero_digs(b->dp + b->used, oldused - b->used);
  
     b->sign = a->sign;
     return MP_OKAY;
  }
  #endif
  

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