kc3-lang/libtommath/mp_mod_2d.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_mod_2d.c

• #include "tommath_private.h"
  #ifdef MP_MOD_2D_C
  /* LibTomMath, multiple-precision integer library -- Tom St Denis */
  /* SPDX-License-Identifier: Unlicense */
  
  /* calc a value mod 2**b */
  mp_err mp_mod_2d(const mp_int *a, int b, mp_int *c)
  {
     int x;
     mp_err err;
  
     if (b < 0) {
        return MP_VAL;
     }
  
     if (b == 0) {
        mp_zero(c);
        return MP_OKAY;
     }
  
     /* if the modulus is larger than the value than return */
     if (b >= (a->used * MP_DIGIT_BIT)) {
        return mp_copy(a, c);
     }
  
     if ((err = mp_copy(a, c)) != MP_OKAY) {
        return err;
     }
  
     /* zero digits above the last digit of the modulus */
     x = (b / MP_DIGIT_BIT) + (((b % MP_DIGIT_BIT) == 0) ? 0 : 1);
     s_mp_zero_digs(c->dp + x, c->used - x);
  
     /* clear the digit that is not completely outside/inside the modulus */
     c->dp[b / MP_DIGIT_BIT] &=
        ((mp_digit)1 << (mp_digit)(b % MP_DIGIT_BIT)) - (mp_digit)1;
     mp_clamp(c);
     return MP_OKAY;
  }
  #endif
  

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