kc3-lang/libtommath/bn_mp_expt_d_ex.c

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• Hash : c098e37e
  Author :
  Date : 2017-10-19T05:51:17
  

  restore previous cast avoid warning with gcc -mx32 left shift count >= width of type [-Wshift-count-overflow] avoid infinite loop at run time

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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(const 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, 1uL);
  
     if (fast != 0) {
        while (b > 0u) {
           /* if the bit is set multiply */
           if ((b & 1u) != 0u) {
              if ((res = mp_mul(c, &g, c)) != MP_OKAY) {
                 mp_clear(&g);
                 return res;
              }
           }
  
           /* square */
           if (b > 1u) {
              if ((res = mp_sqr(&g, &g)) != MP_OKAY) {
                 mp_clear(&g);
                 return res;
              }
           }
  
           /* shift to next bit */
           b >>= 1;
        }
     } else {
        for (x = 0; x < (unsigned)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)1 << (DIGIT_BIT - 1))) != 0u) {
              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
  
  /* ref:         $Format:%D$ */
  /* git commit:  $Format:%H$ */
  /* commit time: $Format:%ai$ */
  

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