text: /*
   * (c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
   * See the copyright notice in the ACK home directory, in the file "Copyright".
   *
   * Author: Ceriel J.H. Jacobs
   */
  
  /* $Header$ */
  
  #define __NO_DEFS
  #include <math.h>
  #include <pc_err.h>
  
  #if __STDC__
  #include <pc_math.h>
  #include <float.h>
  #endif
  #undef HUGE
  #define HUGE	HUGE_VAL
  
  double
  _log(x)
  	double	x;
  {
  	/*	Algorithm and coefficients from:
  			"Software manual for the elementary functions"
  			by W.J. Cody and W. Waite, Prentice-Hall, 1980
  	*/
  	static double a[] = {
  		-0.64124943423745581147e2,
  		 0.16383943563021534222e2,
  		-0.78956112887491257267e0
  	};
  	static double b[] = {
  		-0.76949932108494879777e3,
  		 0.31203222091924532844e3,
  		-0.35667977739034646171e2,
  		 1.0
  	};
  
  	extern double	_fef();
  	double	znum, zden, z, w;
  	int	exponent;
  
  	if (x <= 0) {
  		_trp(ELOG);
  		return -HUGE;
  	}
  
  	x = _fef(x, &exponent);
  	if (x > M_1_SQRT2) {
  		znum = (x - 0.5) - 0.5;
  		zden = x * 0.5 + 0.5;
  	}
  	else {
  		znum = x - 0.5;
  		zden = znum * 0.5 + 0.5;
  		exponent--;
  	}
  	z = znum/zden; w = z * z;
  	x = z + z * w * (POLYNOM2(w,a)/POLYNOM3(w,b));
  	z = exponent;
  	x += z * (-2.121944400546905827679e-4);
  	return x + z * 0.693359375;
  }
  