There are several ways to contribute to MPFR:

- contribute a new mathematical function (see below);
- find, report and fix bugs;
- improve the code coverage and/or contribute new test cases;
- improve the documentation;
- measure and improve the efficiency of the code.

Assume you want to write the code, say `mpfr_foo`

,
for a new mathematical function (say `foo`):

- You (or your employer, depending on your status or your country) first have to agree to donate your contribution to the MPFR project, more precisely to agree with the license used by MPFR, to agree to assign the copyright of your code to the FSF (this page explains why). In addition, if it applies, your employer has to agree to disclaim rights on your contribution.
- You need to define precisely the function you want to implement, in
mathematical terms. For example, the
*dilogarithm*function has different meanings in the literature. Use either a power series, an integral representation... If possible, give references to the literature. - Then you need to choose an algorithm to evaluate the function
`foo`. Write this algorithm, by detailing each atomic operation. Then you have to perform an error analysis of your algorithm (both the mathematical error, i.e., when neglecting terms of a Taylor series, and the roundoff error). See for example the`algorithms.tex`document (PDF version), which contains numerous examples of such algorithms and error analyses. In some cases, you will need different algorithms depending on the output precision and/or on the input range. Please write this description in LaTeX, so that it can easily be included in the`algorithms.tex`document. - Implement in C the algorithm(s) described in the previous step.
You have to follow the following guidelines:
- conform to the ISO C89 and C99 standards;
- conform to the GNU Coding Standards;
- do not use machine floating-point types (
`float`

,`double`

, etc.); - do not use functions defined in
`<math.h>`, since they might give different results on different configurations; - further technical information is available in the
`README.dev`file from the MPFR Subversion repository.

MPFR_CAN_ROUND (approx, approx_err, out_prec, rnd_mode)

- Implement a test program (say
`tfoo.c`) which tests your implementation for correctness. This test program should:- test special values (±0, ±Inf, NaN);
- test exact values, for example
`exp2`

(1) = 2,`sqrt`

(25) = 5, etc.; - test hard-coded values that you have computed with another software
tool, using a large precision. Please input those values in the same
format as in the
`tests/data/exp`file for example. Please indicate if those input/output pair were formally verified. See the`data_check`

function in`tests/tests.c`; - test random values: generate a random number
`x`, compute`foo(x)`

with say`p`bits, then`foo(x)`

with`p`+10 bits, and check that both results are compatible. A useful function that does that automatically is`test_generic`

from`tests/tgeneric.c`; - test bad cases for the correct rounding. If the inverse function
has been implemented, the
`bad_cases`

function from`tests/tests.c`can be used; - test in-place operations, i.e., with same input and
output pointers, like
`mpfr_foo (a, a, ...)`

. See the`reuse.c`test program.

- Write the documentation of the
`mpfr_foo`

function in the file`mpfr.texi`. - (Optional) Test the efficiency of your implementation and compare it to other software tools.
- Send your contribution as a patch (obtained with
`svn diff`

) with respect to the development version to the MPFR developers. They will review your contribution to decide if it will be included in MPFR. In that case, your contribution will be acknowledged in the corresponding source files and in the documentation. - Here is an example of such a patch,
which contributes the
`mpfr_add17`

function to MPFR.