toms451, a Fortran77 code which implements ACM toms algorithm 451, which evaluates quantiles of the Chi-Square probability distribution.
The text of many ACM TOMS algorithms is available online through ACM: https://www.acm.org/pubs/calgo or NETLIB: https://www.netlib.org/toms/index.html.
The information on this web page is distributed under the MIT license.
toms451 is available in a Fortran77 version.
prob, a Fortran90 library which contains numerous routines for handling the Chi square distribution and other probability distributions.
TEST_VALUES, a Fortran90 library which contains routines which return sample values of various functions, including the modified beta function, and the logarithm of the gamma function.