Release builds for GRFCodec are not created anymore. The latest released version can be found on GitHub.
For all binaries officially released by us we publish the MD5, SHA1, and SHA256 checksums. You can use these checksums to check whether the file you downloaded has been modified. All three checksums should match the file you downloaded; if this is not the case it means that either the file didn't come from us or that it got broken during transport. Either way it might possibly contain dangerous modifications and the file should therefore not be trusted!