kc3-lang/libtommath/mp_rshd.c

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• Hash : 795cd201
  Author :
  Date : 2019-10-29T21:48:50
  

  simplifications: add s_mp_zero_(digs|buf) and s_mp_copy_digs Originally I made those as macros. However we have many other small functions like mp_clamp, mp_exch which are also not implemented as macros right now. If we would use c99, I would implement them as private static inline functions. And mp_exch would be a public static inline function. But since we are bound to c89, we simply use normal functions. To achieve optimal performance one should either use link time optimization or amalgamation.

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• mp_rshd.c

• #include "tommath_private.h"
  #ifdef 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;
  
     /* 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.
      * 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++) {
        a->dp[x] = a->dp[x + b];
     }
  
     /* zero the top digits */
     s_mp_zero_digs(a->dp + a->used - b, b);
  
     /* remove excess digits */
     a->used -= b;
  }
  #endif
  

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