/* * (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: /cvsup/minix/src/lib/ack/libp/log.c,v 1.1 2005/10/10 15:27:47 beng Exp $ */#define __NO_DEFS#include <math.h>#include <pc_err.h>#if __STDC__#include <pc_math.h>#include <float.h>#endif#undef HUGE#define HUGE	1e1000double_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;}