@thi.ng/leb128
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WASM based LEB128 encoder / decoder (signed & unsigned)
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# 
[](https://www.npmjs.com/package/@thi.ng/leb128)
[](https://mastodon.thi.ng/@toxi)
> [!NOTE]
> This is one of 215 standalone projects. LLM-free, human-made and
> cared for software, maintained as part of the
> [@thi.ng/umbrella](https://codeberg.org/thi.ng/umbrella/) ecosystem and
> anti-framework.
>
> 🚀 Please help me to work full-time on these projects by [sponsoring
> me](https://codeberg.org/thi.ng/umbrella/src/branch/develop/CONTRIBUTING.md#donations).
> Thank you! ❤️
- [About](#about)
- [Breaking changes](#breaking-changes)
- [Status](#status)
- [Installation](#installation)
- [Dependencies](#dependencies)
- [API](#api)
- [Building the binary](#building-the-binary)
- [Authors](#authors)
- [License](#license)
## About
WASM based [Little Endian Base
128](https://en.wikipedia.org/wiki/LEB128) 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](https://ziglang.org)) is included in
[/zig/leb128.zig](https://codeberg.org/thi.ng/umbrella/src/branch/develop/packages/leb128/zig/leb128.zig)
All public functions throw an error if the WASM module could not be
initialized.
The `encodeSLEB128Into()` and `encodeULEB128Into()` functions will check the
bounds of the target array to ensure all bytes can be written and will
throw an error if the result would go out of bounds.
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](https://codeberg.org/thi.ng/umbrella/issues?q=%5Bleb128%5D)
## Installation
```bash
yarn add @thi.ng/leb128
```
ESM import:
```ts
import * as leb from "@thi.ng/leb128";
```
Browser ESM import:
```html
<script type="module" src="https://esm.run/@thi.ng/leb128"></script>
```
[JSDelivr documentation](https://www.jsdelivr.com/)
For Node.js REPL:
```js
const leb = await import("@thi.ng/leb128");
```
Package sizes (brotli'd, pre-treeshake): ESM: 1.00 KB
## Dependencies
- [@thi.ng/checks](https://codeberg.org/thi.ng/umbrella/src/branch/develop/packages/checks)
- [@thi.ng/errors](https://codeberg.org/thi.ng/umbrella/src/branch/develop/packages/errors)
## API
[Generated API docs](https://docs.thi.ng/umbrella/leb128/)
```ts tangle:export/readme1.ts
import * as leb from "@thi.ng/leb128";
// if WASM is unavailable, the encode/decode functions will throw an error
let encoded = leb.encodeULEB128(Number.MAX_SAFE_INTEGER);
console.log(encoded);
// Uint8Array [ 255, 255, 255, 255, 255, 255, 255, 15 ]
// decoding returns tuple of [value (bigint), bytes consumed]
console.log(leb.decodeULEB128(encoded));
// [ 9007199254740991n, 8 ]
// encode signed int
encoded = leb.encodeSLEB128(Number.MIN_SAFE_INTEGER);
console.log(encoded)
// Uint8Array [ 129, 128, 128, 128, 128, 128, 128, 112 ]
console.log(leb.decodeSLEB128(encoded));
// [ -9007199254740991n, 8 ]
// when writing into an existing buffer, there needs to be enough bytes to write the value
const target = new Uint8Array(10);
const count = leb.encodeULEB128Into(target, Number.MAX_SAFE_INTEGER);
console.log(target);
// Uint8Array [ 255, 255, 255, 255, 255, 255, 255, 15, 0, 0 ]
console.log(count);
// 8
```
## Building the binary
Requirements:
- [Zig](https://ziglang.org/download/)
- [Binaryen](https://github.com/WebAssembly/binaryen)
```bash
# 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
```
## Authors
- [Karsten Schmidt](https://thi.ng) (Main author)
- [jtenner](https://github.com/jtenner)
If this project contributes to an academic publication, please cite it as:
```bibtex
@misc{thing-leb128,
title = "@thi.ng/leb128",
author = "Karsten Schmidt and others",
note = "https://thi.ng/leb128",
year = 2019
}
```
## License
© 2019 - 2026 Karsten Schmidt // Apache License 2.0