kc3-lang/libtommath/bn_mp_expt_d.c

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• Hash : e071a03b
  Author :
  Date : 2011-03-23T20:14:23
  

  Squared result was stored in the wrong variable

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• bn_mp_expt_d.c

• #include <tommath.h>
  #ifdef BN_MP_EXPT_D_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, tomstdenis@gmail.com, http://libtom.org
   */
  
  /* calculate c = a**b  using a square-multiply algorithm */
  int mp_expt_d (mp_int * a, mp_digit b, mp_int * c)
  {
    int     res;
    mp_int  g;
  
    if ((res = mp_init_copy (&g, a)) != MP_OKAY) {
      return res;
    }
  
    /* set initial result */
    mp_set (c, 1);
  
    while (b > 0) {
      /* if the bit is set multiply */
      if (b & 1) {
        if ((res = mp_mul (c, &g, c)) != MP_OKAY) {
          mp_clear (&g);
          return res;
        }
      }
  
      /* square */
      if (b > 1 && (res = mp_sqr (&g, &g)) != MP_OKAY) {
        mp_clear (&g);
        return res;
      }
  
      /* shift to next bit */
      b >>= 1;
    }
  
    mp_clear (&g);
    return MP_OKAY;
  }
  #endif
  
  /* $Source$ */
  /* $Revision$ */
  /* $Date$ */
  

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