base64

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A SIMD-accelerated drop-in replacement for Go's encoding/base64.

Overview

This package keeps the same public API and behavior as Go's standard encoding/base64, while using architecture-specific SIMD implementations where available.

• Compatible with StdEncoding, URLEncoding, RawStdEncoding, RawURLEncoding, NewEncoding, WithPadding, Strict, stream encoder/decoder, and append helpers.
• Uses runtime CPU feature detection on supported platforms.
• Falls back to the generic Go implementation when SIMD is unavailable or the input is too small for the optimized path.

Supported Architectures

Architecture	SIMD path
AMD64	SSE, AVX2, AVX512 VBMI
ARM64	NEON
PPC64X	VSX / VMX (AltiVec)
S390X	Vector Facility
LOONG64	LSX, LASX
RISCV64	RVV

The concrete path is selected automatically at runtime based on CPU features.

Installation

go get github.com/emmansun/base64

Usage

Import this package instead of encoding/base64:

package main

import (
	"fmt"

	"github.com/emmansun/base64"
)

func main() {
	src := []byte("hello, world")

	enc := base64.StdEncoding.EncodeToString(src)
	dec, err := base64.StdEncoding.DecodeString(enc)
	if err != nil {
		panic(err)
	}

	fmt.Println(enc)
	fmt.Println(string(dec))
}

Because the exported API follows the standard library, existing code usually only needs an import path change.

Behavior Notes

• Encoding and decoding semantics follow RFC 4648, matching Go's standard library behavior.
• Strict decoding is supported through Encoding.Strict().
• Raw encodings without padding are supported through RawStdEncoding, RawURLEncoding, or WithPadding(base64.NoPadding).
• Inputs containing \r or \n are handled the same way as the standard library, but decode throughput may not improve for newline-heavy data.

Performance

Performance depends on CPU model, microarchitecture, input size, encoding variant, and input shape. This repository does not publish a single benchmark table because numbers are hardware-dependent.

If performance matters for your workload, run benchmarks on your target machines.

Project Status

• The package is tested in CI across the architectures covered by this repository.
• AMD64 AVX512 VBMI coverage is also validated with Intel SDE in CI.

Acknowledgements

Most of the generic Go implementation is derived from golang base64.

The amd64 implementation, especially the SSE path, and the arm64 SIMD implementation were inspired by aklomp/base64.