sysdeps/ieee754/dbl-64/slowexp.c

   1 /*
   2  * IBM Accurate Mathematical Library
   3  * written by International Business Machines Corp.
   4  * Copyright (C) 2001 Free Software Foundation
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU Lesser General Public License as published by
   8  * the Free Software Foundation; either version 2.1 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  19  */
  20 /**************************************************************************/
  21 /*  MODULE_NAME:slowexp.c                                                 */
  22 /*                                                                        */
  23 /*  FUNCTION:slowexp                                                      */
  24 /*                                                                        */
  25 /*  FILES NEEDED:mpa.h                                                    */
  26 /*               mpa.c mpexp.c                                            */
  27 /*                                                                        */
  28 /*Converting from double precision to Multi-precision and calculating     */
  29 /* e^x                                                                    */
  30 /**************************************************************************/
  31 #include "mpa.h"
  32 #include "math_private.h"
  33
  34 void __mpexp(mp_no *x, mp_no *y, int p);
  35
  36 /*Converting from double precision to Multi-precision and calculating  e^x */
  37 double __slowexp(double x) {
  38   double w,z,res,eps=3.0e-26;
  39 #if 0
  40   double y;
  41 #endif
  42   int p;
  43 #if 0
  44   int orig,i;
  45 #endif
  46   mp_no mpx, mpy, mpz,mpw,mpeps,mpcor;
  47
  48   p=6;
  49   __dbl_mp(x,&mpx,p); /* Convert a double precision number  x               */
  50                     /* into a multiple precision number mpx with prec. p. */
  51   __mpexp(&mpx, &mpy, p); /* Multi-Precision exponential function */
  52   __dbl_mp(eps,&mpeps,p);
  53   __mul(&mpeps,&mpy,&mpcor,p);
  54   __add(&mpy,&mpcor,&mpw,p);
  55   __sub(&mpy,&mpcor,&mpz,p);
  56   __mp_dbl(&mpw, &w, p);
  57   __mp_dbl(&mpz, &z, p);
  58   if (w == z) return w;
  59   else  {                   /* if calculating is not exactly   */
  60     p = 32;
  61     __dbl_mp(x,&mpx,p);
  62     __mpexp(&mpx, &mpy, p);
  63     __mp_dbl(&mpy, &res, p);
  64     return res;
  65   }
  66 }