kc3-lang/libtommath/s_mp_log_d.c

• Show log

  Commit

• Hash : 1cc289d2
  Author :
  Date : 2019-11-09T20:23:03
  

  better use of mp_isneg() and mp_iszero()

Download

• s_mp_log_d.c

• #include "tommath_private.h"
  #ifdef S_MP_LOG_D_C
  /* LibTomMath, multiple-precision integer library -- Tom St Denis */
  /* SPDX-License-Identifier: Unlicense */
  
  static mp_word s_pow(mp_word base, mp_word exponent)
  {
     mp_word result = 1u;
     while (exponent != 0u) {
        if ((exponent & 1u) == 1u) {
           result *= base;
        }
        exponent >>= 1;
        base *= base;
     }
  
     return result;
  }
  
  mp_digit s_mp_log_d(mp_digit base, mp_digit n)
  {
     mp_word bracket_low = 1u, bracket_mid, bracket_high, N;
     mp_digit ret, high = 1uL, low = 0uL, mid;
  
     if (n < base) {
        return 0uL;
     }
     if (n == base) {
        return 1uL;
     }
  
     bracket_high = (mp_word) base ;
     N = (mp_word) n;
  
     while (bracket_high < N) {
        low = high;
        bracket_low = bracket_high;
        high <<= 1;
        bracket_high *= bracket_high;
     }
  
     while (((mp_digit)(high - low)) > 1uL) {
        mid = (low + high) >> 1;
        bracket_mid = bracket_low * s_pow(base, (mp_word)(mid - low));
  
        if (N < bracket_mid) {
           high = mid ;
           bracket_high = bracket_mid ;
        }
        if (N > bracket_mid) {
           low = mid ;
           bracket_low = bracket_mid ;
        }
        if (N == bracket_mid) {
           return (mp_digit) mid;
        }
     }
  
     if (bracket_high == N) {
        ret = high;
     } else {
        ret = low;
     }
  
     return ret;
  }
  
  #endif
  

Download