kc3-lang/libtommath/bn_mp_expt_d_ex.c

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• Hash : 4534056c
  Author :
  Date : 2019-05-13T00:22:18
  

  use enums mp_err, mp_ord, mp_bool, mp_sign * MP_USE_ENUMS enables enums * Wc++-compat catches some implicit conversions if MP_USE_ENUMS is defined * 100% backwards compatible API/ABI if MP_USE_ENUMS is not defined

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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 */
  /* SPDX-License-Identifier: Unlicense */
  
  /* calculate c = a**b  using a square-multiply algorithm */
  mp_err mp_expt_d_ex(const mp_int *a, mp_digit b, mp_int *c, int fast)
  {
     mp_err 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)MP_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 << (MP_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
  

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