leb128

LEB128

This gem is a set of utility functions for encoding and decoding LEB128-compressed integers.

As a visual example, this is an excerpt from the LEB128 Wikipedia page describing how an integer is encoded into an unsigned LEB128:

      10011000011101100101  In raw binary
     010011000011101100101  Padded to a multiple of 7 bits
 0100110  0001110  1100101  Split into 7-bit groups
00100110 10001110 11100101  Add high 1 bits on all but last group to form bytes
    0x26     0x8E     0xE5  In hexadecimal
0xE5 0x8E 0x26              Output stream

Installation

Add this line to your application's Gemfile:

gem 'leb128'

And then execute:

$ bundle

Or install it yourself as:

$ gem install leb128

Usage

Require the Gem:

require 'leb128'

Encoding and Decoding

Encode integers into LEB128-compressed data by using the encode_unsigned and encode_signed methods. The functions take one argument, being the integer to encode. The following encodes the given integer and returns a new StringIO containing it:

LEB128.encode_signed(-0x143f)
#=> #<StringIO:0x00000000000000>

Decode LEB128-compressed data into integers by using the decode_unsigned and decode_signed methods. The functions take two arguments: a StringIO containing the LEB128-compressed data, and an optional integer that sets the position of the StringIO (default is 0). The following decodes the given StringIO and returns a new integer containing it:

sio = StringIO.new
sio.putc(0xc1)
sio.putc(0x57)
LEB128.decode_unsigned(sio)
#=> 11201

License

This gem is available as open source under the terms of the MIT License. See LICENSE.md and https://opensource.org/licenses/MIT.