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Diffstat (limited to 'sysdeps/ieee754/dbl-64/slowpow.c')
| -rw-r--r-- | sysdeps/ieee754/dbl-64/slowpow.c | 73 |
1 files changed, 73 insertions, 0 deletions
diff --git a/sysdeps/ieee754/dbl-64/slowpow.c b/sysdeps/ieee754/dbl-64/slowpow.c new file mode 100644 index 0000000..efb6072 --- /dev/null +++ b/sysdeps/ieee754/dbl-64/slowpow.c @@ -0,0 +1,73 @@ + +/* + * 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; +} |