This project is part of the @thi.ng/umbrella monorepo.
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:
- https://en.wikipedia.org/wiki/LEB128
- http://webassembly.github.io/spec/core/binary/values.html#integers
yarn add @thi.ng/leb128import * as leb from "@thi.ng/leb128";
// since WASM initialization is async, need to wait until module is ready...
// if WASM is unavailable, the encode/decode functions will throw an error
leb.READY.then(()=> {
// encode unsigned int (input val up to 64 bits)
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 ]
});# 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
echo "export const BINARY = \"$(base64 -i opt.wasm)\";" > src/binary.ts
# test TS/JS version
yarn test- Karsten Schmidt
© 2019 Karsten Schmidt // Apache Software License 2.0