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/* @(#)s_logb.c 5.1 93/09/24 */

/*

 * ====================================================

 * 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.

 * ====================================================

 */

#if defined(LIBM_SCCS) && !defined(lint)

static char rcsid[] = "$NetBSD: s_logb.c,v 1.8 1995/05/10 20:47:50 jtc Exp $";

#endif

/*

 * double logb(x)

 * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.

 * Use ilogb instead.

 */

#include "math.h"

#include "math_private.h"

#ifdef __STDC__

        double logb(double x)

#else

        double logb(x)

        double x;

#endif

{

        int32_t lx,ix;

        EXTRACT_WORDS(ix,lx,x);

        ix &= 0x7fffffff;                       /* high |x| */

        if((ix|lx)==0) return -1.0/fabs(x);

        if(ix>=0x7ff00000) return x*x;

        if((ix>>=20)==0)                         /* IEEE 754 logb */

                return -1022.0;

        else

                return (double) (ix-1023);

}