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Diffstat (limited to 'mpfr/src/log10.c')
| -rw-r--r-- | mpfr/src/log10.c | 150 |
1 files changed, 150 insertions, 0 deletions
diff --git a/mpfr/src/log10.c b/mpfr/src/log10.c new file mode 100644 index 0000000000..31b6ce9f6e --- /dev/null +++ b/mpfr/src/log10.c @@ -0,0 +1,150 @@ +/* mpfr_log10 -- logarithm in base 10. + +Copyright 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc. +Contributed by the AriC and Caramel projects, INRIA. + +This file is part of the GNU MPFR Library. + +The GNU MPFR Library 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 3 of the License, or (at your +option) any later version. + +The GNU MPFR Library 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 the GNU MPFR Library; see the file COPYING.LESSER. If not, see +http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc., +51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */ + +#define MPFR_NEED_LONGLONG_H +#include "mpfr-impl.h" + + /* The computation of r=log10(a) + + r=log10(a)=log(a)/log(10) + */ + +int +mpfr_log10 (mpfr_ptr r, mpfr_srcptr a, mpfr_rnd_t rnd_mode) +{ + int inexact; + MPFR_SAVE_EXPO_DECL (expo); + + MPFR_LOG_FUNC + (("a[%Pu]=%.*Rg rnd=%d", mpfr_get_prec (a), mpfr_log_prec, a, rnd_mode), + ("r[%Pu]=%.*Rg inexact=%d", + mpfr_get_prec (r), mpfr_log_prec, r, inexact)); + + /* If a is NaN, the result is NaN */ + if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (a))) + { + if (MPFR_IS_NAN (a)) + { + MPFR_SET_NAN (r); + MPFR_RET_NAN; + } + /* check for infinity before zero */ + else if (MPFR_IS_INF (a)) + { + if (MPFR_IS_NEG (a)) + /* log10(-Inf) = NaN */ + { + MPFR_SET_NAN (r); + MPFR_RET_NAN; + } + else /* log10(+Inf) = +Inf */ + { + MPFR_SET_INF (r); + MPFR_SET_POS (r); + MPFR_RET (0); /* exact */ + } + } + else /* a = 0 */ + { + MPFR_ASSERTD (MPFR_IS_ZERO (a)); + MPFR_SET_INF (r); + MPFR_SET_NEG (r); + mpfr_set_divby0 (); + MPFR_RET (0); /* log10(0) is an exact -infinity */ + } + } + + /* If a is negative, the result is NaN */ + if (MPFR_UNLIKELY (MPFR_IS_NEG (a))) + { + MPFR_SET_NAN (r); + MPFR_RET_NAN; + } + + /* If a is 1, the result is 0 */ + if (mpfr_cmp_ui (a, 1) == 0) + { + MPFR_SET_ZERO (r); + MPFR_SET_POS (r); + MPFR_RET (0); /* result is exact */ + } + + MPFR_SAVE_EXPO_MARK (expo); + + /* General case */ + { + /* Declaration of the intermediary variable */ + mpfr_t t, tt; + MPFR_ZIV_DECL (loop); + /* Declaration of the size variable */ + mpfr_prec_t Ny = MPFR_PREC(r); /* Precision of output variable */ + mpfr_prec_t Nt; /* Precision of the intermediary variable */ + mpfr_exp_t err; /* Precision of error */ + + /* compute the precision of intermediary variable */ + /* the optimal number of bits : see algorithms.tex */ + Nt = Ny + 4 + MPFR_INT_CEIL_LOG2 (Ny); + + /* initialise of intermediary variables */ + mpfr_init2 (t, Nt); + mpfr_init2 (tt, Nt); + + /* First computation of log10 */ + MPFR_ZIV_INIT (loop, Nt); + for (;;) + { + /* compute log10 */ + mpfr_set_ui (t, 10, MPFR_RNDN); /* 10 */ + mpfr_log (t, t, MPFR_RNDD); /* log(10) */ + mpfr_log (tt, a, MPFR_RNDN); /* log(a) */ + mpfr_div (t, tt, t, MPFR_RNDN); /* log(a)/log(10) */ + + /* estimation of the error */ + err = Nt - 4; + if (MPFR_LIKELY (MPFR_CAN_ROUND (t, err, Ny, rnd_mode))) + break; + + /* log10(10^n) is exact: + FIXME: Can we have 10^n exactly representable as a mpfr_t + but n can't fit an unsigned long? */ + if (MPFR_IS_POS (t) + && mpfr_integer_p (t) && mpfr_fits_ulong_p (t, MPFR_RNDN) + && !mpfr_ui_pow_ui (tt, 10, mpfr_get_ui (t, MPFR_RNDN), MPFR_RNDN) + && mpfr_cmp (a, tt) == 0) + break; + + /* actualisation of the precision */ + MPFR_ZIV_NEXT (loop, Nt); + mpfr_set_prec (t, Nt); + mpfr_set_prec (tt, Nt); + } + MPFR_ZIV_FREE (loop); + + inexact = mpfr_set (r, t, rnd_mode); + + mpfr_clear (t); + mpfr_clear (tt); + } + + MPFR_SAVE_EXPO_FREE (expo); + return mpfr_check_range (r, inexact, rnd_mode); +} |