math.c

来自「linux平台下类似著名的电路板作图软件 Spice的源代码」· C语言 代码 · 共 87 行

/**********
Copyright 1991 Regents of the University of California.  All rights reserved.
**********/

/*
 * Missing math functions
 */

#include "spice.h"
#include "stdio.h"
#include "misc.h"
#include "suffix.h"

#ifdef HAS_NO_IEEE_LOGB

double
logb(x)
	double	x;
{
	double	y = 0.0;

	if (x != 0.0) {
		if (x < 0.0)
			x = - x;
		while (x > 2.0) {
			y += 1.0;
			x /= 2.0;
		}
		while (x < 1.0) {
			y -= 1.0;
			x *= 2.0;
		}
	} else
		y = 0.0;

	return y;
}

double
scalb(x, n)
	double	x;
	int	n;
{
	double	y, z = 1.0, k = 2.0;

	if (n < 0) {
		n = -n;
		k = 0.5;
	}

	if (x != 0.0)
		for (y = 1.0; n; n >>= 1) {
			y *= k;
			if (n & 1)
				z *= y;
		}

	return x * z;
}

#endif

#ifdef HAS_NO_ERFC
/* From C. Hastings, Jr., Approximations for digital computers,
	Princeton Univ. Press, 1955.
   Approximation accurate to within 1.5E-7
   (making some assumptions about your machine's floating point mechanism)
*/

double
erfc(x)
	double  x;
{
	double t, z;

	t =  1/(1 + 0.3275911*x);
	z =  1.061405429;
	z = -1.453152027 + t * z;
	z =  1.421413741 + t * z;
	z = -0.284496736 + t * z;
	z =  0.254829592 + t * z;
	z =  exp(-x*x) * t * z;

	return(z);
}
#endif