kc3-lang/libtommath/bn_mp_rshd.c

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• Hash : 1af0de1f
  Author :
  Date : 2019-05-20T19:11:25
  

  deprecate mp_tc_(and|or|xor) in favor of mp_(and|or|xor) * same behavior for positive numbers * generalisation for negative numbers, treating them as two complement * improve algorithm, iterate once over the digits, manually perform two complement * simplify mp_add_d, mp_sub_d * functions are safe in case of a==c or b==c * renamed mp_tc_div_2d to mp_signed_rsh (signed right shift)

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• bn_mp_rshd.c

• #include "tommath_private.h"
  #ifdef BN_MP_RSHD_C
  /* LibTomMath, multiple-precision integer library -- Tom St Denis */
  /* SPDX-License-Identifier: Unlicense */
  
  /* shift right a certain amount of digits */
  void mp_rshd(mp_int *a, int b)
  {
     int     x;
     mp_digit *bottom, *top;
  
     /* if b <= 0 then ignore it */
     if (b <= 0) {
        return;
     }
  
     /* if b > used then simply zero it and return */
     if (a->used <= b) {
        mp_zero(a);
        return;
     }
  
     /* shift the digits down */
  
     /* bottom */
     bottom = a->dp;
  
     /* top [offset into digits] */
     top = a->dp + b;
  
     /* this is implemented as a sliding window where
      * the window is b-digits long and digits from
      * the top of the window are copied to the bottom
      *
      * e.g.
  
      b-2 | b-1 | b0 | b1 | b2 | ... | bb |   ---->
                  /\                   |      ---->
                   \-------------------/      ---->
      */
     for (x = 0; x < (a->used - b); x++) {
        *bottom++ = *top++;
     }
  
     /* zero the top digits */
     MP_ZERO_DIGITS(bottom, a->used - x);
  
     /* remove excess digits */
     a->used -= b;
  }
  #endif
  

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