toms243 is a C library which evaluates the logarithm of a complex value, by David Collens. This is a version of ACM TOMS algorithm 243.

The text of many ACM TOMS algorithms is available online through ACM: or NETLIB:


The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.


TOMS243 is available in a C version and a C++ version and a FORTRAN90 version and a MATLAB version and a Python version.

Related Data and Programs:

test_values, a C library which tabulates several values of a variety of special functions.



  1. David Collens,
    Algorithm 243: Logarithm of a Complex Number,
    Communications of the Association for Computing Machinery,
    Volume 7, Number 11, November 1964, page 660.

Source Code:

Last revised on 04 January 2019.