src/math/s_ilogb.c


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

/* ilogb(double x)
 * return the binary exponent of non-zero x
 * ilogb(0) = FP_ILOGB0
 * ilogb(NaN) = FP_ILOGBNAN (no signal is raised)
 * ilogb(inf) = INT_MAX (no signal is raised)
 */

#include <limits.h>

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

int ilogb(double x)
{
        int32_t hx,lx,ix;

        EXTRACT_WORDS(hx,lx,x);
        hx &= 0x7fffffff;
        if(hx<0x00100000) {
            if((hx|lx)==0)
                return FP_ILOGB0;
            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 if (hx>0x7ff00000 || lx!=0) return FP_ILOGBNAN;
        else return INT_MAX;
}