kc3-lang/libtommath/bn_mp_montgomery_calc_normalization.c

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• Hash : 99c84acc
  Author :
  Date : 2015-11-13T10:28:23
  

  add parentheses for explicit operator precedence

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• bn_mp_montgomery_calc_normalization.c

• #include <tommath_private.h>
  #ifdef BN_MP_MONTGOMERY_CALC_NORMALIZATION_C
  /* LibTomMath, multiple-precision integer library -- Tom St Denis
   *
   * LibTomMath is a library that provides multiple-precision
   * integer arithmetic as well as number theoretic functionality.
   *
   * The library was designed directly after the MPI library by
   * Michael Fromberger but has been written from scratch with
   * additional optimizations in place.
   *
   * The library is free for all purposes without any express
   * guarantee it works.
   *
   * Tom St Denis, tstdenis82@gmail.com, http://libtom.org
   */
  
  /*
   * shifts with subtractions when the result is greater than b.
   *
   * The method is slightly modified to shift B unconditionally upto just under
   * the leading bit of b.  This saves alot of multiple precision shifting.
   */
  int mp_montgomery_calc_normalization (mp_int * a, mp_int * b)
  {
    int     x, bits, res;
  
    /* how many bits of last digit does b use */
    bits = mp_count_bits (b) % DIGIT_BIT;
  
    if (b->used > 1) {
       if ((res = mp_2expt (a, ((b->used - 1) * DIGIT_BIT) + bits - 1)) != MP_OKAY) {
          return res;
       }
    } else {
       mp_set(a, 1);
       bits = 1;
    }
  
  
    /* now compute C = A * B mod b */
    for (x = bits - 1; x < (int)DIGIT_BIT; x++) {
      if ((res = mp_mul_2 (a, a)) != MP_OKAY) {
        return res;
      }
      if (mp_cmp_mag (a, b) != MP_LT) {
        if ((res = s_mp_sub (a, b, a)) != MP_OKAY) {
          return res;
        }
      }
    }
  
    return MP_OKAY;
  }
  #endif
  
  /* $Source$ */
  /* $Revision$ */
  /* $Date$ */
  

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