share/doc/mpfr/BUGS

Copyright 1999, 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.

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Known bugs:

* The overflow/underflow exceptions may be badly handled in some functions;
  specially when the intermediary internal results have exponent which
  exceeds the hardware limit (2^30 for a 32 bits CPU, and 2^62 for a 64 bits
  CPU) or the exact result is close to an overflow/underflow threshold.

* Under Linux/x86 with the traditional FPU, some functions do not work
  if the FPU rounding precision has been changed to single (this is a
  bad practice and should be useless, but one never knows what other
  software will do).

* Some functions do not use MPFR_SAVE_EXPO_* macros, thus do not behave
  correctly in a reduced exponent range.

* Function hypot gives incorrect result when on the one hand the difference
  between parameters' exponents is near 2*MPFR_EMAX_MAX and on the other hand
  the output precision or the precision of the parameter with greatest
  absolute value is greater than 2*MPFR_EMAX_MAX-4.

Potential bugs:

* Possible incorrect results due to internal underflow, which can lead to
  a huge loss of accuracy while the error analysis doesn't take that into
  account. If the underflow occurs at the last function call (just before
  the MPFR_CAN_ROUND), the result should be correct (or MPFR gets into an
  infinite loop). TODO: check the code and the error analysis.

* Possible integer overflows on some machines.

* Possible bugs with huge precisions (> 2^30).

* Possible bugs if the chosen exponent range does not allow to represent
  the range [1/16, 16].

* Possible infinite loop in some functions for particular cases: when
  the exact result is an exactly representable number or the middle of
  consecutive two such numbers. However for non-algebraic functions, it is
  believed that no such case exists, except the well-known cases like cos(0)=1,
  exp(0)=1, and so on, and the x^y function when y is an integer or y=1/2^k.

* The mpfr_set_ld function may be quite slow if the long double type has an
  exponent of more than 15 bits.

* mpfr_set_d may give wrong results on some non-IEEE architectures.

* Error analysis for some functions may be incorrect (out-of-date due
  to modifications in the code?).

* Possible use of non-portable feature (pre-C99) of the integer division
  with negative result.