/home/jaouen/pok_official/pok/trunk/libpok/libm/logb.c

/*
 *                               POK header
 * 
 * The following file is a part of the POK project. Any modification should
 * made according to the POK licence. You CANNOT use this file or a part of
 * this file is this part of a file for your own project
 *
 * For more information on the POK licence, please see our LICENCE FILE
 *
 * Please follow the coding guidelines described in doc/CODING_GUIDELINES
 *
 *                                      Copyright (c) 2007-2009 POK team 
 *
 * Created by julien on Fri Jan 30 14:41:34 2009 
 */

/* @(#)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.
 * ====================================================
 */


/*
 * double logb(x)
 * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
 * Use ilogb instead.
 */

#ifdef POK_NEEDS_LIBMATH

#include <libm.h>
#include "math_private.h"

double
logb(double x)
{
        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);
}

#endif