A nearly drop-in replacement for Go's slow-ass base64 implementation, using aklomp/base64, an awesome SIMD-accelerated library.
However, it does not skip whitespace and other junk characters!
SkipPrepass is provided to deal with that, but it slows everything down.
(Still up to 2x as fast as the standard library.)
AMD Ryzen 7 1700 @ 3.9 GHz (AVX2)
go 1.9.1, FreeBSD 12-CURRENT
BenchmarkEncodeStdlib-16 1000000 1600 ns/op 1279.65 MB/s
BenchmarkEncodeSIMD-16 5000000 321 ns/op 6361.63 MB/s
BenchmarkDecodeStdlib-16 200000 6499 ns/op 315.10 MB/s
BenchmarkDecodeSIMD-16 3000000 455 ns/op 4500.07 MB/s
BenchmarkDecodeSIMDWithSkipPrepassNoSpace-16 500000 2850 ns/op 718.45 MB/s
BenchmarkDecodeSIMDWithSkipPrepassLineWrapped-16 300000 5432 ns/op 509.20 MB/s
Intel Xeon E3-1220 @ 3.10GHz (AVX)
go 1.8.3, Linux 3.10.0
BenchmarkEncodeStdlib-4 500000 2474 ns/op 827.64 MB/s
BenchmarkEncodeSIMD-4 3000000 481 ns/op 4257.22 MB/s
BenchmarkDecodeStdlib-4 100000 13995 ns/op 146.33 MB/s
BenchmarkDecodeSIMD-4 3000000 531 ns/op 3851.89 MB/s
BenchmarkDecodeSIMDWithSkipPrepassNoSpace-4 200000 6913 ns/op 296.23 MB/s
BenchmarkDecodeSIMDWithSkipPrepassLineWrapped-4 200000 9869 ns/op 280.26 MB/s
This should use assembly but currently uses cgo.
Initially I attempted to use the terrible yet amazing c2goasm hack.
It does not support global array constants.
I've tried to bolt that on, but couldn't figure out how to express addressing like mov al, byte ptr [rax + base64_table_enc] in Go's horrific assembly syntax.
Then I've discovered the .syso thing where you can link to objects assembled by a reasonable assembler.
Gave up fighting the crashes that came with that approach, using cgo for now, but still with the .syso file.
BSD, like the original aklomp/base64 C library.