This R package implements an approximate method to calculate the p-value for the Anderson-Darling test for uniformity based on J. and G. Marsaglia's 2004 paper "Evaluating the Anderson-Darling Distribution".
You can find it in CRAN and can be installed using R's install.package function.
The project summary page can be found here. You may also be interested in its page at crantastic.
The package has been developed by Carlos J. Gil Bellosta.