sf_ilogb.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_ilogb.c -- float version of s_ilogb.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"
#include <limits.h>

#ifdef __STDC__
	int ilogbf(float x)
#else
	int ilogbf(x)
	float x;
#endif
{
	__int32_t hx,ix;

	GET_FLOAT_WORD(hx,x);
	hx &= 0x7fffffff;
	if(hx<0x00800000) {
	    if(hx==0) 
		return - INT_MAX;	/* ilogb(0) = 0x80000001 */
	    else			/* subnormal x */
	        for (ix = -126,hx<<=8; hx>0; hx<<=1) ix -=1;
	    return ix;
	}
	else if (hx<0x7f800000) return (hx>>23)-127;
	else return INT_MAX;
}