js/src/fdlibm/s_modf.c

   1 /* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
   2  *
   3  * ***** BEGIN LICENSE BLOCK *****
   4  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
   5  *
   6  * The contents of this file are subject to the Mozilla Public License Version
   7  * 1.1 (the "License"); you may not use this file except in compliance with
   8  * the License. You may obtain a copy of the License at
   9  * http://www.mozilla.org/MPL/
  10  *
  11  * Software distributed under the License is distributed on an "AS IS" basis,
  12  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
  13  * for the specific language governing rights and limitations under the
  14  * License.
  15  *
  16  * The Original Code is Mozilla Communicator client code, released
  17  * March 31, 1998.
  18  *
  19  * The Initial Developer of the Original Code is
  20  * Sun Microsystems, Inc.
  21  * Portions created by the Initial Developer are Copyright (C) 1998
  22  * the Initial Developer. All Rights Reserved.
  23  *
  24  * Contributor(s):
  25  *
  26  * Alternatively, the contents of this file may be used under the terms of
  27  * either of the GNU General Public License Version 2 or later (the "GPL"),
  28  * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
  29  * in which case the provisions of the GPL or the LGPL are applicable instead
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  38  * ***** END LICENSE BLOCK ***** */
  39
  40 /* @(#)s_modf.c 1.3 95/01/18 */
  41 /*
  42  * ====================================================
  43  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
  44  *
  45  * Developed at SunSoft, a Sun Microsystems, Inc. business.
  46  * Permission to use, copy, modify, and distribute this
  47  * software is freely granted, provided that this notice
  48  * is preserved.
  49  * ====================================================
  50  */
  51
  52 /*
  53  * modf(double x, double *iptr)
  54  * return fraction part of x, and return x's integral part in *iptr.
  55  * Method:
  56  *      Bit twiddling.
  57  *
  58  * Exception:
  59  *      No exception.
  60  */
  61
  62 #include "fdlibm.h"
  63
  64 #ifdef __STDC__
  65 static const double one = 1.0;
  66 #else
  67 static double one = 1.0;
  68 #endif
  69
  70 #ifdef __STDC__
  71         double fd_modf(double x, double *iptr)
  72 #else
  73         double fd_modf(x, iptr)
  74         double x,*iptr;
  75 #endif
  76 {
  77         int i0,i1,j0;
  78         unsigned i;
  79         fd_twoints u;
  80         u.d = x;
  81         i0 =  __HI(u);          /* high x */
  82         i1 =  __LO(u);          /* low  x */
  83         j0 = ((i0>>20)&0x7ff)-0x3ff;    /* exponent of x */
  84         if(j0<20) {                     /* integer part in high x */
  85             if(j0<0) {                  /* |x|<1 */
  86                 u.d = *iptr;
  87                 __HI(u) = i0&0x80000000;
  88                 __LO(u) = 0;            /* *iptr = +-0 */
  89                 *iptr = u.d;
  90                 return x;
  91             } else {
  92                 i = (0x000fffff)>>j0;
  93                 if(((i0&i)|i1)==0) {            /* x is integral */
  94                     *iptr = x;
  95                     u.d = x;
  96                     __HI(u) &= 0x80000000;
  97                     __LO(u)  = 0;       /* return +-0 */
  98                     x = u.d;
  99                     return x;
 100                 } else {
 101                     u.d = *iptr;
 102                     __HI(u) = i0&(~i);
 103                     __LO(u) = 0;
 104                     *iptr = u.d;
 105                     return x - *iptr;
 106                 }
 107             }
 108         } else if (j0>51) {             /* no fraction part */
 109             *iptr = x*one;
 110             u.d = x;
 111             __HI(u) &= 0x80000000;
 112             __LO(u)  = 0;       /* return +-0 */
 113             x = u.d;
 114             return x;
 115         } else {                        /* fraction part in low x */
 116             i = ((unsigned)(0xffffffff))>>(j0-20);
 117             if((i1&i)==0) {             /* x is integral */
 118                 *iptr = x;
 119                 u.d = x;
 120                 __HI(u) &= 0x80000000;
 121                 __LO(u)  = 0;   /* return +-0 */
 122                 x = u.d;
 123                 return x;
 124             } else {
 125                 u.d = *iptr;
 126                 __HI(u) = i0;
 127                 __LO(u) = i1&(~i);
 128                 *iptr = u.d;
 129                 return x - *iptr;
 130             }
 131         }
 132 }