The latest (2.18) glibc source code could be downloaded from http://ftp.gnu.org/gnu/glibc/glibc-2.18.tar.gz. ERF is very well hidden inside the archive... Look at glibc-2.18\sysdeps\ieee754\dbl-64\. If you were able to compile it under windows we may prevent some result differences while running the application under different platforms.

The name of the directory tree suggest that this is a x64 version (maybe not, maybe there is a x32 one).