1  /* log1p(x) = log(1+x).  The log1p function is designed to avoid the
       2     significant loss of precision that arises from direct evaluation when x is
       3     small. Use the substitute from _math.h on all platforms: it includes
       4     workarounds for buggy handling of zeros.
       5   */
       6  
       7  static double
       8  _Py_log1p(double x)
       9  {
      10      /* Some platforms supply a log1p function but don't respect the sign of
      11         zero:  log1p(-0.0) gives 0.0 instead of the correct result of -0.0.
      12  
      13         To save fiddling with configure tests and platform checks, we handle the
      14         special case of zero input directly on all platforms.
      15      */
      16      if (x == 0.0) {
      17          return x;
      18      }
      19      else {
      20          return log1p(x);
      21      }
      22  }
      23  
      24  #define m_log1p _Py_log1p