sf_ilogb.c

Newlib 嵌入式 C库 标准实现代码

/* 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(FLT_UWORD_IS_ZERO(hx))
	    return - INT_MAX;	/* ilogb(0) = 0x80000001 */
	if(FLT_UWORD_IS_SUBNORMAL(hx)) {
	    for (ix = -126,hx<<=8; hx>0; hx<<=1) ix -=1;
	    return ix;
	}
	else if (!FLT_UWORD_IS_FINITE(hx)) return INT_MAX;
	else return (hx>>23)-127;
}

#ifdef _DOUBLE_IS_32BITS

#ifdef __STDC__
	int ilogb(double x)
#else
	int ilogb(x)
	double x;
#endif
{
	return ilogbf((float) x);
}

#endif /* defined(_DOUBLE_IS_32BITS) */