ef_atanh.c

来自「Newlib 嵌入式 C库 标准实现代码」· C语言 代码 · 共 55 行

/* ef_atanh.c -- float version of e_atanh.c.
 * Conversion to float by Ian Lance Taylor, Cygnus Support, [e-mail].
 */

/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice 
 * is preserved.
 * ====================================================
 *
 */

#include "fdlibm.h"

#ifdef __STDC__
static const float one = 1.0, huge = 1e30;
#else
static float one = 1.0, huge = 1e30;
#endif

#ifdef __STDC__
static const float zero = 0.0;
#else
static float zero = 0.0;
#endif

#ifdef __STDC__
	float atanhf(float x)
#else
	float atanhf(x)
	float x;
#endif
{
	float t;
	__int32_t hx,ix;
	GET_FLOAT_WORD(hx,x);
	ix = hx&0x7fffffff;
	if (ix>0x3f800000) 		/* |x|>1 */
	    return (x-x)/(x-x);
	if(ix==0x3f800000) 
	    return x/zero;
	if(ix<0x31800000&&(huge+x)>zero) return x;	/* x<2**-28 */
	SET_FLOAT_WORD(x,ix);
	if(ix<0x3f000000) {		/* x < 0.5 */
	    t = x+x;
	    t = (float)0.5*log1pf(t+t*x/(one-x));
	} else 
	    t = (float)0.5*log1pf((x+x)/(one-x));
	if(hx>=0) return t; else return -t;
}