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lightning-sunbird  0.9+nobinonly
s_ilogb.c
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00001 /* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
00002  *
00003  * ***** BEGIN LICENSE BLOCK *****
00004  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
00005  *
00006  * The contents of this file are subject to the Mozilla Public License Version
00007  * 1.1 (the "License"); you may not use this file except in compliance with
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00009  * http://www.mozilla.org/MPL/
00010  *
00011  * Software distributed under the License is distributed on an "AS IS" basis,
00012  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
00013  * for the specific language governing rights and limitations under the
00014  * License.
00015  *
00016  * The Original Code is Mozilla Communicator client code, released
00017  * March 31, 1998.
00018  *
00019  * The Initial Developer of the Original Code is
00020  * Sun Microsystems, Inc.
00021  * Portions created by the Initial Developer are Copyright (C) 1998
00022  * the Initial Developer. All Rights Reserved.
00023  *
00024  * Contributor(s):
00025  *
00026  * Alternatively, the contents of this file may be used under the terms of
00027  * either of the GNU General Public License Version 2 or later (the "GPL"),
00028  * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
00029  * in which case the provisions of the GPL or the LGPL are applicable instead
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00037  *
00038  * ***** END LICENSE BLOCK ***** */
00039 
00040 /* @(#)s_ilogb.c 1.3 95/01/18 */
00041 /*
00042  * ====================================================
00043  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
00044  *
00045  * Developed at SunSoft, a Sun Microsystems, Inc. business.
00046  * Permission to use, copy, modify, and distribute this
00047  * software is freely granted, provided that this notice 
00048  * is preserved.
00049  * ====================================================
00050  */
00051 
00052 /* ilogb(double x)
00053  * return the binary exponent of non-zero x
00054  * ilogb(0) = 0x80000001
00055  * ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
00056  */
00057 
00058 #include "fdlibm.h"
00059 
00060 #ifdef __STDC__
00061        int fd_ilogb(double x)
00062 #else
00063        int fd_ilogb(x)
00064        double x;
00065 #endif
00066 {
00067        int hx,lx,ix;
00068         fd_twoints u;
00069         u.d = x;
00070        hx  = (__HI(u))&0x7fffffff; /* high word of x */
00071        if(hx<0x00100000) {
00072            lx = __LO(u);
00073            if((hx|lx)==0) 
00074               return 0x80000001;   /* ilogb(0) = 0x80000001 */
00075            else                    /* subnormal x */
00076               if(hx==0) {
00077                   for (ix = -1043; lx>0; lx<<=1) ix -=1;
00078               } else {
00079                   for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
00080               }
00081            return ix;
00082        }
00083        else if (hx<0x7ff00000) return (hx>>20)-1023;
00084        else return 0x7fffffff;
00085 }