c3-lang/libtommath/bn_mp_expt_d_ex.c

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• Hash : 4e3f1344
  Author :
  Date : 2015-11-12T01:49:07
  

  provide tommath_private.h tommath.h contains declarations for the public part of the library. tommath_private.h contains the functions which are private to ltm and should not be exposed to the public.

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• bn_mp_expt_d_ex.c

• #include <tommath_private.h>
  #ifdef BN_MP_EXPT_D_EX_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
   */
  
  /* calculate c = a**b  using a square-multiply algorithm */
  int mp_expt_d_ex (mp_int * a, mp_digit b, mp_int * c, int fast)
  {
    int     res;
    unsigned int x;
  
    mp_int  g;
  
    if ((res = mp_init_copy (&g, a)) != MP_OKAY) {
      return res;
    }
  
    /* set initial result */
    mp_set (c, 1);
  
    if (fast != 0) {
      while (b > 0) {
        /* if the bit is set multiply */
        if ((b & 1) != 0) {
          if ((res = mp_mul (c, &g, c)) != MP_OKAY) {
            mp_clear (&g);
            return res;
          }
        }
  
        /* square */
        if (b > 1) {
          if ((res = mp_sqr (&g, &g)) != MP_OKAY) {
            mp_clear (&g);
            return res;
          }
        }
  
        /* shift to next bit */
        b >>= 1;
      }
    }
    else {
      for (x = 0; x < DIGIT_BIT; x++) {
        /* square */
        if ((res = mp_sqr (c, c)) != MP_OKAY) {
          mp_clear (&g);
          return res;
        }
  
        /* if the bit is set multiply */
        if ((b & (mp_digit) (((mp_digit)1) << (DIGIT_BIT - 1))) != 0) {
          if ((res = mp_mul (c, &g, c)) != MP_OKAY) {
             mp_clear (&g);
             return res;
          }
        }
  
        /* shift to next bit */
        b <<= 1;
      }
    } /* if ... else */
  
    mp_clear (&g);
    return MP_OKAY;
  }
  #endif
  
  /* $Source$ */
  /* $Revision$ */
  /* $Date$ */
  

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