source: vendor/FreeBSD-msun/5.x-2005-06-xx/src/s_ilogbl.c

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

#ifndef lint
static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_ilogbl.c,v 1.1 2004/10/11 18:13:52 stefanf Exp $";
#endif

#include <float.h>
#include <limits.h>
#include <math.h>

#include "fpmath.h"

int
ilogbl(long double x)
{
        union IEEEl2bits u;
        unsigned long m;
        int b;

        u.e = x;
        if (u.bits.exp == 0) {
                if ((u.bits.manl | u.bits.manh) == 0)
                        return (FP_ILOGB0);
                /* denormalized */
                if (u.bits.manh == 0) {
                        m = 1lu << (LDBL_MANL_SIZE - 1);
                        for (b = LDBL_MANH_SIZE; !(u.bits.manl & m); m >>= 1)
                                b++;
                } else {
                        m = 1lu << (LDBL_MANH_SIZE - 1);
                        for (b = 0; !(u.bits.manh & m); m >>= 1)
                                b++;
                }
#ifdef LDBL_IMPLICIT_NBIT
                b++;
#endif
                return (LDBL_MIN_EXP - b - 1);
        } else if (u.bits.exp < (LDBL_MAX_EXP << 1) - 1)
                return (u.bits.exp - LDBL_MAX_EXP + 1);
        else if (u.bits.manl != 0 || u.bits.manh != 0)
                return (FP_ILOGBNAN);
        else
                return (INT_MAX);
}