# The bigfloat package — high precision floating-point arithmetic¶

Release v0.4.0-dev.

The bigfloat package is a Python wrapper for the GNU MPFR library for arbitrary-precision floating-point reliable arithmetic. The MPFR library is a well-known portable C library for arbitrary-precision arithmetic on floating-point numbers. It provides precise control over precisions and rounding modes and gives correctly-rounded reproducible platform-independent results.

The bigfloat package aims to provide a convenient and friendly Python interface to the operations and functions provided by the MPFR library. The main class, BigFloat, gives an immutable multiple-precision floating-point type that can be freely mixed with Python integers and floats. The Context class, when used in conjunction with Python’s with statement, gives a simple way of controlling precisions and rounding modes. Additional module-level functions provide various standard mathematical operations. There is full support for IEEE 754 signed zeros, nans, infinities and subnormals.

## Features¶

• Supports Python 2 (version 2.7) and Python 3 (version 3.4 or later).
• Exactly reproducible correctly-rounded results across platforms; precisely-defined semantics compatible with the IEEE 754-2008 standard.
• Support for mixed-type operations with Python integers and floats.
• Support for emulating IEEE 754 arithmetic in any of the IEEE binary interchange formats described in IEEE 754-2008. Infinities, NaNs, signed zeros, and subnormals are all supported.
• Easy control of rounding modes and precisions via Context objects and Python’s with statement.

## Introduction¶

Here’s a quick tour:

>>> from bigfloat import *
>>> sqrt(2, precision(100))  # compute sqrt(2) with 100 bits of precision
BigFloat.exact('1.4142135623730950488016887242092', precision=100)
>>> with precision(100):     # another way to get the same result
...     sqrt(2)
...
BigFloat.exact('1.4142135623730950488016887242092', precision=100)
>>> my_context = precision(100) + RoundTowardPositive
>>> my_context
Context(precision=100, rounding='RoundTowardPositive')
>>> sqrt(2, my_context)      # and another, this time rounding up
BigFloat.exact('1.4142135623730950488016887242108', precision=100)
>>> with RoundTowardNegative: # a lower bound for zeta(2)
...     sum(1/sqr(n) for n in range(1, 10000))
...
BigFloat.exact('1.6448340618469506', precision=53)
>>> zeta(2) # actual value, for comparison
BigFloat.exact('1.6449340668482264', precision=53)
>>> const_pi()**2/6.0  # double check value
BigFloat.exact('1.6449340668482264', precision=53)
>>> quadruple_precision  # context implementing IEEE 754 binary128 format
Context(precision=113, emax=16384, emin=-16493, subnormalize=True)
>>> next_up(0, quadruple_precision)  # smallest subnormal for binary128
BigFloat.exact('6.47517511943802511092443895822764655e-4966', precision=113)
>>> log2(_)
BigFloat.exact('-16494.000000000000', precision=53)


## Installation¶

### Where to get it¶

The latest released version of the bigfloat package can be obtained from the Python Package Index. Development sources can be checked out from the project’s GitHub page.

### Prerequisites¶

The bigfloat package works with Python 2 (version 2.7) or Python 3 (version 3.4 or later). It uses a single codebase for both Python dialects, so the same source works on both dialects of Python.

Whether installing bigfloat from source or from the Python Package Index, you will need to have both the GMP and MPFR libraries already installed on your system, along with the include files for those libraries. See the MPFR homepage and the GMP homepage for more information about these libraries. Currently, MPFR version 3.0.0 or later is required.

On Ubuntu, prerequisites can be installed with:

sudo apt-get install libmpfr-dev


On Fedora Linux, use (for example):

su -c "yum install mpfr-devel"


On other flavours of Linux, some variant of one of the above should work.

### Installation from the Python Package Index¶

Once you have the prerequisites described above installed, the recommended method for installation is to use pip:

pip install bigfloat


If you prefer, you can use the easy_install command from setuptools:

easy-install bigfloat


Depending on your system, you may need superuser privileges for the install. For example:

sudo pip install bigfloat


If the MPFR and GMP libraries are installed in an unusual location, you may need to set appropriate environment variables when installing. For example, on an OS X 10.9 system with MPFR and GMP installed in /opt/local, I need to do:

sudo LIBRARY_PATH=/opt/local/lib CPATH=/opt/local/include pip install bigfloat


### Platform-specific installation instructions¶

On a newly-installed version of Ubuntu 14.04LTS (trusty), the commands below are enough to install bigfloat for Python 3, from scratch. You may not need the first line if you already have pip and the Python development headers installed.

sudo apt-get install python3-dev python3-pip
sudo apt-get install libmpfr-dev
sudo pip3 install bigfloat


For Python 2, the procedure is similar:

sudo apt-get install python-dev python-pip
sudo apt-get install libmpfr-dev
sudo pip install bigfloat


On Fedora 20, the following sequence of commands worked for me (for Python 3; again, remove all occurrences of 3 to get the commands for Python 2):

su -c "yum install gcc python3-devel python3-pip"
su -c "yum install mpfr-devel"
su -c "pip-python3 install bigfloat"


### Installation from source¶

Installation from source (for example, from a GitHub checkout, or from an unpacked source distribution), is similar to installation from the Python Package Index: the only difference is that you should use the setup.py  script instead of using pip or easy_install. On many systems, installation should be as simple as typing:

python setup.py install


in the top-level directory of the unpacked distribution. As above, you may need superuser privileges to install the library, for example with:

sudo python setup.py install


Again as above, if the libraries and include files are installed in an unusual place, it may be necessary to specify their location using environment variables on the command line. For example:

LIBRARY_PATH=/opt/local/lib CPATH=/opt/local/include python setup.py install