Roadmap

go-ruby-base64/base64 is grown test-first, each capability differential-tested against MRI rather than built in isolation. Ruby's Base64 module — the deterministic, interpreter-independent slice of require "base64" — is complete.

Stage	What	Status
Encode64	RFC 2045 (pack("m")): the standard +/ alphabet, a newline every 60 output characters, and a trailing newline; the empty string encodes to empty.	Done
Decode64 (lenient)	String#unpack1("m"): non-alphabet bytes skipped, padding optional, a = on a partial quad finalises and stops decoding, a = on a quad boundary ignored, a lone orphaned final sextet discarded.	Done
Strict variants	StrictEncode64 (pack("m0")) emits no newlines; StrictDecode64 (unpack1("m0")) rejects any stray byte — including the newlines encoding/base64 tolerates — with ErrInvalid.	Done
Url-safe variants	UrlsafeEncode64 / UrlsafeDecode64 on the -_ alphabet (RFC 4648); padding on by default and stripped when padding=false; decode accepts padded or unpadded input and rejects everything else.	Done
SIMD acceleration	The hot standard-alphabet bodies route through go-simd/base64's go-asmgen kernels (amd64 SSE/AVX2, arm64 NEON, ppc64le VSX, s390x vector; stdlib fallback elsewhere) — CGO=0 SIMD across all six 64-bit arches, bit-identical to StdEncoding.	Done
Differential oracle & coverage	A wide corpus — every length class, a line wrap, non-ASCII bytes, malformed/strict inputs — driven through the system ruby and asserted byte-equal; 100% coverage, gofmt + go vet clean, green across all six 64-bit Go arches and three OSes.	Done

Documented out-of-scope boundaries

These are deliberate, recorded so the module's surface is unambiguous:

• No interpreter. The library implements the deterministic encode/decode algorithm over Go strings; it never runs arbitrary Ruby. Binding the methods to a live Ruby Base64 module — argument coercion, raising ArgumentError — is the consumer's job, which is why rbgo binds this module rather than the reverse.
• Go errors, not exceptions. The strict decoders return a Go error (ErrInvalid); mapping it to MRI's ArgumentError is the host's job.
• Reference is reference Ruby (MRI 4.0.5). Byte-for-byte conformance targets MRI's behaviour, pinned by the differential oracle; the SIMD path stays bit-identical to encoding/base64.StdEncoding.

See Usage & API for the surface and Why pure Go for the deterministic/SIMD split.