Base62.jl

A Julia package for Base62 encoding and decoding of binary data, closely mirroring the API of Julia's standard library Base64.

Alphabet

Base62 uses the 62 alphanumeric characters in lexicographic (ASCII) order:

0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz

Important: Value 0 maps to '0', not 'A'. This differs from some Base62 implementations that use Base64-compatible ordering (A-Za-z0-9). We use 0-9A-Za-z — the natural ASCII/lexicographic order.

Unlike Base64, there are no padding characters (=) and no special symbols (+, /, -, _). This makes Base62 strings safe for URLs, filenames, identifiers, and any context requiring only alphanumerics.

Algorithm

The encoding uses big-integer arithmetic with 32-byte chunking (inspired by petersmagnusson/base62):

• Input is split into 32-byte chunks
• Each chunk is converted to a BigInt and encoded via repeated division by 62
• Output is zero-padded so that encoded length is deterministic — it depends only on input byte length, never on content
• 32 bytes → 43 base62 characters (same as Base64!)

Installation

using Pkg
Pkg.add(url="https://github.com/HomogeneousTools/Base62.jl")

Or in the Pkg REPL (]):

add https://github.com/HomogeneousTools/Base62.jl

Usage

using Base62

# Encode a string
encoded = base62encode("Hello!")    # "0MbPS3UBt"

# Decode back
decoded = String(base62decode(encoded))  # "Hello!"

# Encode raw bytes
base62encode(UInt8[0x01, 0x02, 0x03])  # "00HBL"

# Pipe-based encoding (mirrors Base64 API)
io = IOBuffer()
pipe = Base62EncodePipe(io)
write(pipe, "Hello World!")
close(pipe)
encoded = String(take!(io))  # "0T8dgcjRGkZ3aysdN"

# Pipe-based decoding
pipe = Base62DecodePipe(IOBuffer(encoded))
result = String(read(pipe))  # "Hello World!"

API Reference

Function / Type	Description
base62encode(x)	Encode data to a Base62 string
base62decode(s)	Decode a Base62 string to Vector{UInt8}
Base62EncodePipe	Write-only IO pipe that encodes to Base62
Base62DecodePipe	Read-only IO pipe that decodes from Base62

Acknowledgments

This implementation was created using Claude Opus 4.6 by combining ideas from several existing Base62/Base64 implementations:

• Julia Base64 stdlib — The API design (pipe-based IO with Base62EncodePipe/Base62DecodePipe, base62encode/base62decode convenience functions) closely mirrors Julia's standard library Base64 module.
• petersmagnusson/base62 (TypeScript) — The 32-byte chunking strategy and deterministic output length design (zero-padded, content-independent) originate from this implementation.
• fbernier/base62 (Rust) — The two-at-a-time encoding (pre-computed 62×62 pairs table) and two-at-a-time decoding optimizations that halve the number of BigInt operations per chunk were inspired by this high-performance Rust crate.

License

MIT