GLEB128 is a small Gleam library that provides functions for encoding and decoding LEB128 (Little Endian Base 128) integers. LEB128 is a variable-length code compression method used to store arbitrarily large integers in a small number of bytes. Notable use cases for LEB128 are in the DWARF debug file format and the WebAssembly's binary format.

import gleam/io
import gleb128

pub fn main()
{
    let unsigned_encoded = gleb128.encode_unsigned(255)
    let signed_encoded = gleb128.encode_signed(-255)

    io.debug(unsigned_encoded)
    io.debug(signed_encoded)
}

Shows the following in output:

Ok(<<255, 1>>)
<<129, 126>>

Which corresponds, in hexadecimal, respectively, to <<0xff, 0x01>> and <<0x81, 0x7e>>.

The decoding functions returns a Result wrapping a tuple containing the decoded value in its first position, followed by the count of bytes read in its second position.

import gleam/io
import gleb128

pub fn main()
{
    let unsigned_decoded = gleb128.decode_unsigned(<<255, 1, 4, 80, 64>>) // actually <<4, 80, 64>> will be ignored, so only the first two bytes will be read
    let signed_decoded = gleb128.decode_signed(<<129, 126>>)

    io.debug(unsigned_decoded)
    io.debug(signed_decoded)
}

Shows the following in output:

Ok(#(255, 2))
Ok(#(-255, 2))

The fast_decode_unsigned and fast_decode_signed functions are optimized for decoding small LEB128 integers on 64-bit systems. Those functions will treat and process the data as a native integer when its length is less than or equal to 8 bytes (64 bits); otherwise, they will fallback to the default decoding functions.

On a Ryzen 5 5600G with 32 GB RAM, encoding and then decoding all numbers in the range from 0 to 100000000 with the default decode_signed took 50.10 seconds and used about 20 GB of memory. Repeating the test using fast_decode_signed reduced the elapsed time to 40.16 seconds and memory usage to about 14.5 GB. The fast_decode_unsigned function can be even faster when targeting Erlang, as it can use its stdlib's built-in binary:decode_unsigned/2 function.

GLEB128 source code is avaliable under the MIT license.