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 (e.g. MacOS X 10.8, see gh-59682) supply a log1p function
      11         but don't respect the sign of zero:  log1p(-0.0) gives 0.0 instead of
      12         the correct result of -0.0.
      13  
      14         To save fiddling with configure tests and platform checks, we handle the
      15         special case of zero input directly on all platforms.
      16      */
      17      if (x == 0.0) {
      18          return x;
      19      }
      20      else {
      21          return log1p(x);
      22      }
      23  }
      24  
      25  #define m_log1p _Py_log1p