sf_logb.c

标准c库代码,可以应用于各个系统提供了大量的基本函数

/* sf_logb.c -- float version of s_logb.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__
	float logbf(float x)
#else
	float logbf(x)
	float x;
#endif
{
	__int32_t ix;
	GET_FLOAT_WORD(ix,x);
	ix &= 0x7fffffff;			/* high |x| */
	if(ix==0) return (float)-1.0/fabsf(x);
	if(ix>=0x7f800000) return x*x;
	if((ix>>=23)==0) 			/* IEEE 754 logb */
		return -126.0; 
	else
		return (float) (ix-127); 
}