74 lines
3.3 KiB
C
74 lines
3.3 KiB
C
|
|
||
|
/*
|
||
|
* IBM Accurate Mathematical Library
|
||
|
* Copyright (c) International Business Machines Corp., 2001
|
||
|
*
|
||
|
* This program is free software; you can redistribute it and/or modify
|
||
|
* it under the terms of the GNU Lesser General Public License as published by
|
||
|
* the Free Software Foundation; either version 2 of the License, or
|
||
|
* (at your option) any later version.
|
||
|
*
|
||
|
* This program is distributed in the hope that it will be useful,
|
||
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
||
|
* GNU General Public License for more details.
|
||
|
*
|
||
|
* You should have received a copy of the GNU Lesser General Public License
|
||
|
* along with this program; if not, write to the Free Software
|
||
|
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
|
||
|
*/
|
||
|
/*************************************************************************/
|
||
|
/* MODULE_NAME:slowpow.c */
|
||
|
/* */
|
||
|
/* FUNCTION:slowpow */
|
||
|
/* */
|
||
|
/*FILES NEEDED:mpa.h */
|
||
|
/* mpa.c mpexp.c mplog.c halfulp.c */
|
||
|
/* */
|
||
|
/* Given two IEEE double machine numbers y,x , routine computes the */
|
||
|
/* correctly rounded (to nearest) value of x^y. Result calculated by */
|
||
|
/* multiplication (in halfulp.c) or if result isn't accurate enough */
|
||
|
/* then routine converts x and y into multi-precision doubles and */
|
||
|
/* calls to mpexp routine */
|
||
|
/*************************************************************************/
|
||
|
|
||
|
#include "mpa.h"
|
||
|
|
||
|
void mpexp(mp_no *x, mp_no *y, int p);
|
||
|
void mplog(mp_no *x, mp_no *y, int p);
|
||
|
double ulog(double);
|
||
|
double halfulp(double x,double y);
|
||
|
|
||
|
double slowpow(double x, double y, double z) {
|
||
|
double res,res1;
|
||
|
mp_no mpx, mpy, mpz,mpw,mpp,mpr,mpr1;
|
||
|
static const mp_no eps = {-3,1.0,4.0};
|
||
|
int p;
|
||
|
|
||
|
res = halfulp(x,y); /* halfulp() returns -10 or x^y */
|
||
|
if (res >= 0) return res; /* if result was really computed by halfulp */
|
||
|
/* else, if result was not really computed by halfulp */
|
||
|
p = 10; /* p=precision */
|
||
|
dbl_mp(x,&mpx,p);
|
||
|
dbl_mp(y,&mpy,p);
|
||
|
dbl_mp(z,&mpz,p);
|
||
|
mplog(&mpx, &mpz, p); /* log(x) = z */
|
||
|
mul(&mpy,&mpz,&mpw,p); /* y * z =w */
|
||
|
mpexp(&mpw, &mpp, p); /* e^w =pp */
|
||
|
add(&mpp,&eps,&mpr,p); /* pp+eps =r */
|
||
|
mp_dbl(&mpr, &res, p);
|
||
|
sub(&mpp,&eps,&mpr1,p); /* pp -eps =r1 */
|
||
|
mp_dbl(&mpr1, &res1, p); /* converting into double precision */
|
||
|
if (res == res1) return res;
|
||
|
|
||
|
p = 32; /* if we get here result wasn't calculated exactly, continue */
|
||
|
dbl_mp(x,&mpx,p); /* for more exact calculation */
|
||
|
dbl_mp(y,&mpy,p);
|
||
|
dbl_mp(z,&mpz,p);
|
||
|
mplog(&mpx, &mpz, p); /* log(c)=z */
|
||
|
mul(&mpy,&mpz,&mpw,p); /* y*z =w */
|
||
|
mpexp(&mpw, &mpp, p); /* e^w=pp */
|
||
|
mp_dbl(&mpp, &res, p); /* converting into double precision */
|
||
|
return res;
|
||
|
}
|