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@thi.ng/leb128

leb128

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This project is part of the @thi.ng/umbrella monorepo.

About

WASM based Little Endian Base 128 varint encoding / decoding, supporting (u)int64 range (however for JS purposes only up to MAX_SAFE_INTEGER).

The WASM binary (~660 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 /src/leb128.zig

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

References:

Status

STABLE - used in production

Installation

yarn add @thi.ng/leb128
// ES module
<script type="module" src="https://unpkg.com/@thi.ng/leb128?module" crossorigin></script>

// UMD
<script src="https://unpkg.com/@thi.ng/leb128/lib/index.umd.js" crossorigin></script>

Package sizes (gzipped, pre-treeshake): ESM: 988 bytes / CJS: 1.04 KB / UMD: 1.10 KB

Dependencies

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, bytes consumed]
leb.decodeULEB128(enc);
// [ 9007199254740991, 8 ]

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

leb.decodeSLEB128(enc)
// [ -9007199254740991, 8 ]

Building the binary

# download latest master from https://ziglang.org/download/

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

# compile to WASM (requires zig v0.4.0 or later)
zig build-lib -target wasm32-freestanding --release-small --strip src/leb128.zig

# apply binaryen optimizer
wasm-opt leb128.wasm -o opt.wasm -Os

# display as .wat text format
wasm2wat opt.wasm

# base64 encode and generate src/binary.ts
yarn build:binary

# test TS/JS version
yarn test

Authors

Karsten Schmidt

License

© 2019 - 2020 Karsten Schmidt // Apache Software License 2.0

Generated using TypeDoc