#  [](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 ``` [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