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• About
• Breaking changes
• Status
• Installation
• Dependencies
• API
• Building the binary
• Authors
• License

About

WASM based Little Endian Base 128 varint encoding / decoding, supporting the full (u)int64 range.

The WASM binary (~860 bytes) is embedded as base64 string in the TypeScript source to make it easier to use in both browser & node environments. The source code of the actual implementation (written in Zig) is included in /zig/leb128.zig

All public functions throw an error if the WASM module could not be initialized.

References:

• https://en.wikipedia.org/wiki/LEB128
• http://webassembly.github.io/spec/core/binary/values.html#integers

Breaking changes

v3.0.0 introduces JS bigint support and both decode functions return a tuple of [bigint, number] with the bigint being the decoded value and the 2nd item the number of bytes consumed. Simarly, the encode functions now accept a JS number or bigint arg.

Furthermore, all values to be encoded/decoded are cast to i64/u64 range now.

Status

STABLE - used in production

Search or submit any issues for this package

Installation

yarn add @thi.ng/leb128
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ES module import:

<script type="module" src="https://cdn.skypack.dev/@thi.ng/leb128"></script>
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Skypack documentation

For Node.js REPL:

const leb128 = await import("@thi.ng/leb128");
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Package sizes (brotli'd, pre-treeshake): ESM: 880 bytes

Dependencies

• @thi.ng/checks
• @thi.ng/errors
• @thi.ng/transducers-binary

API

Generated API docs

import * as leb from "@thi.ng/leb128";

// if WASM is unavailable, the encode/decode functions will throw an error
enc = leb.encodeULEB128(Number.MAX_SAFE_INTEGER);
// Uint8Array [ 255, 255, 255, 255, 255, 255, 255, 15 ]

// decoding returns tuple of [value (bigint), bytes consumed]
leb.decodeULEB128(enc);
// [ 9007199254740991n, 8 ]

// encode signed int
enc = leb.encodeSLEB128(Number.MIN_SAFE_INTEGER)
// Uint8Array [ 129, 128, 128, 128, 128, 128, 128, 112 ]

leb.decodeSLEB128(enc)
// [ -9007199254740991n, 8 ]
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Building the binary

Requirements:

• Zig
• Binaryen

# install required tools
brew install zig binaryen

# first run native tests
zig test zig/leb128.zig
# Test 1/2 min safe integer...OK
# Test 2/2 max safe integer...OK
# All tests passed.

# build binary and regenerate src/binary.ts
yarn build:binary

# test TS/JS version
yarn test
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Authors

• Karsten Schmidt

If this project contributes to an academic publication, please cite it as:

@misc{thing-leb128,
  title = "@thi.ng/leb128",
  author = "Karsten Schmidt",
  note = "https://thi.ng/leb128",
  year = 2019
}
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License

© 2019 - 2024 Karsten Schmidt // Apache License 2.0