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Diffstat (limited to 'REORG.TODO/sysdeps/ieee754/dbl-64/mplog.c')
| -rw-r--r-- | REORG.TODO/sysdeps/ieee754/dbl-64/mplog.c | 65 |
1 files changed, 65 insertions, 0 deletions
diff --git a/REORG.TODO/sysdeps/ieee754/dbl-64/mplog.c b/REORG.TODO/sysdeps/ieee754/dbl-64/mplog.c new file mode 100644 index 0000000000..5b03117d07 --- /dev/null +++ b/REORG.TODO/sysdeps/ieee754/dbl-64/mplog.c @@ -0,0 +1,65 @@ +/* + * IBM Accurate Mathematical Library + * written by International Business Machines Corp. + * Copyright (C) 2001-2017 Free Software Foundation, Inc. + * + * 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 2.1 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 Lesser 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, see <http://www.gnu.org/licenses/>. + */ +/************************************************************************/ +/* */ +/* 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 +__mplog (mp_no *x, mp_no *y, int p) +{ + int i, m; + 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 mpt1, mpt2; + + /* Choose m. */ + m = mp[p]; + + /* 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); + } +} |