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lightning-sunbird  0.9+nobinonly
s_scalbn.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
00008  * the License. You may obtain a copy of the License at
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
00030  * of those above. If you wish to allow use of your version of this file only
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00035  * the provisions above, a recipient may use your version of this file under
00036  * the terms of any one of the MPL, the GPL or the LGPL.
00037  *
00038  * ***** END LICENSE BLOCK ***** */
00039 
00040 /* @(#)s_scalbn.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 /* 
00053  * scalbn (double x, int n)
00054  * scalbn(x,n) returns x* 2**n  computed by  exponent  
00055  * manipulation rather than by actually performing an 
00056  * exponentiation or a multiplication.
00057  */
00058 
00059 #include "fdlibm.h"
00060 
00061 #ifdef __STDC__
00062 static const double
00063 #else
00064 static double
00065 #endif
00066 two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
00067 twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
00068 really_big   = 1.0e+300,
00069 tiny   = 1.0e-300;
00070 
00071 #ifdef __STDC__
00072        double fd_scalbn (double x, int n)
00073 #else
00074        double fd_scalbn (x,n)
00075        double x; int n;
00076 #endif
00077 {
00078         fd_twoints u;
00079        int  k,hx,lx;
00080         u.d = x;
00081        hx = __HI(u);
00082        lx = __LO(u);
00083         k = (hx&0x7ff00000)>>20;          /* extract exponent */
00084         if (k==0) {                       /* 0 or subnormal x */
00085             if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
00086            x *= two54;
00087             u.d = x;
00088            hx = __HI(u);
00089            k = ((hx&0x7ff00000)>>20) - 54; 
00090             if (n< -50000) return tiny*x;        /*underflow*/
00091            }
00092         if (k==0x7ff) return x+x;         /* NaN or Inf */
00093         k = k+n; 
00094         if (k >  0x7fe) return really_big*fd_copysign(really_big,x); /* overflow  */
00095         if (k > 0)                        /* normal result */
00096            {u.d = x; __HI(u) = (hx&0x800fffff)|(k<<20); x = u.d; return x;}
00097         if (k <= -54) {
00098             if (n > 50000)  /* in case integer overflow in n+k */
00099               return really_big*fd_copysign(really_big,x);     /*overflow*/
00100            else return tiny*fd_copysign(tiny,x);        /*underflow*/
00101         }
00102         k += 54;                          /* subnormal result */
00103         u.d = x;
00104         __HI(u) = (hx&0x800fffff)|(k<<20);
00105         x = u.d;
00106         return x*twom54;
00107 }