usr/share/doc/mpfr/BUGS

Copyright 1999, 2001-2015 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.

##############################################################################

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.