I\'ve been trying to figure out the openssl documentation for base64 decoding and encoding. I found some code snippets below
Base64 is really pretty simple; you shouldn't have trouble finding any number of implementations via a quick Google. For example here is a reference implementation in C from the Internet Software Consortium, with detailed comments explaining the process.
The openssl implementation layers a lot of complexity with the "BIO" stuff that's not (IMHO) very useful if all you're doing is decoding/encoding.