s_ilogb.c

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
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/* ilogb(double x)
 * return the binary exponent of non-zero x
 * ilogb(0) = 0x80000001
 * ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
 */

#include "fdlibm.h"

#ifdef __STDC__
        int ilogb(double x)
#else
        int ilogb(x)
        double x;
#endif
{
        int hx,lx,ix;

        hx  = (__HI(x))&0x7fffffff;     /* high word of x */
        if(hx<0x00100000) {
            lx = __LO(x);
            if((hx|lx)==0)
                return 0x80000001;      /* ilogb(0) = 0x80000001 */
            else                        /* subnormal x */
                if(hx==0) {
                    for (ix = -1043; lx>0; lx<<=1) ix -=1;
                } else {
                    for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
                }
            return ix;
        }
        else if (hx<0x7ff00000) return (hx>>20)-1023;
        else return 0x7fffffff;
}