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Diffstat (limited to 'sysdeps/ieee754/dbl-64/mplog.c')
| -rw-r--r-- | sysdeps/ieee754/dbl-64/mplog.c | 68 |
1 files changed, 68 insertions, 0 deletions
diff --git a/sysdeps/ieee754/dbl-64/mplog.c b/sysdeps/ieee754/dbl-64/mplog.c new file mode 100644 index 0000000000..78aec799f2 --- /dev/null +++ b/sysdeps/ieee754/dbl-64/mplog.c @@ -0,0 +1,68 @@ + +/* + * 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:mplog.c */ +/* */ +/* FUNCTIONS: mplog */ +/* */ +/* FILES NEEDED: endian.h mpa.h mplog.h */ +/* mpexp.c */ +/* */ +/* Multi-Precision logarithm function subroutine (for precision p >= 4, */ +/* 2**(-1024) < x < 2**1024) and x is outside of the interval */ +/* [1-2**(-54),1+2**(-54)]. Upon entry, x should be set to the */ +/* multi-precision value of the input and y should be set into a multi- */ +/* precision value of an approximation of log(x) with relative error */ +/* bound of at most 2**(-52). The routine improves the accuracy of y. */ +/* */ +/************************************************************************/ +#include "endian.h" +#include "mpa.h" + +void mpexp(mp_no *, mp_no *, int); + +void mplog(mp_no *x, mp_no *y, int p) { +#include "mplog.h" + int i,j,k,m,m1,m2,n; + double a,b; + static const int mp[33] = {0,0,0,0,0,1,1,2,2,2,2,3,3,3,3,3,3,3,3, + 4,4,4,4,4,4,4,4,4,4,4,4,4,4}; + mp_no mpone = {0, 0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0, + 0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0, + 0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,}; + mp_no mpt1,mpt2; + + /* Choose m and initiate mpone */ + m = mp[p]; mpone.e = 1; mpone.d[0]=mpone.d[1]=ONE; + + /* Perform m newton iterations to solve for y: exp(y)-x=0. */ + /* The iterations formula is: y(n+1)=y(n)+(x*exp(-y(n))-1). */ + cpy(y,&mpt1,p); + for (i=0; i<m; i++) { + mpt1.d[0]=-mpt1.d[0]; + mpexp(&mpt1,&mpt2,p); + mul(x,&mpt2,&mpt1,p); + sub(&mpt1,&mpone,&mpt2,p); + add(y,&mpt2,&mpt1,p); + cpy(&mpt1,y,p); + } + return; +} |