The benchmarks shows the 'generic' aka SWAR version w or w/o openmp is the best for almost all purposes. The only thing I would change is the func sig to size_t

The benchmarks shows the 'generic' aka SWAR version w or w/o openmp is the best for almost all purposes. The only thing I would change is the func sig to size_t base64_enc(const char * src, char * dst, size_t len) to ret written size.