Algorithm 743: WAPR--a Fortran routine for calculating real values of the W -function
D. A. Barry, S. J. Barry, Patricia J. Culligan · ACM Transactions on Mathematical Software · 1995
We implement W -function approximation scheme described by Barry et al. A range of tests of the approximations is included so that the code can be assessed on any given machine. Users can calculate W(x) by specifying x itself or by specifying an offset from −exp(−1), the latter option necessitated by rounding errors that can arise for x close to −exp(−1). Results of running the code on a SUN workstation are included.