small_ints

small_ints is an Erlang module that can help you deal with encoding and decoding of integers using the varint and ZigZag algorithms described in the "Encoding" section of Google Protocol Buffer's docs.

Building

$ rebar3 compile

Varint

Basically, you use a variable number of bytes to represent a positive integer. You can encode varints to binaries and decode them from binaries like this:

small_ints:encode_varint(5).    %=> <<5>>
small_ints:encode_varint(1034). %=> <<138,8>>

small_ints:decode_varint(<<5,"foo">>). %=> {5, <<"foo">>}
small_ints:decode_varint(<<138,8>>). %=> {1034, <<>>}

ZigZag

The ZigZag algorithm is used to encode small positive and negative numbers with a small number of bytes.

small_ints:encode_zigzag(1).  %=> 2
small_ints:encode_zigzag(-5). %=> 9

small_ints:decode_zigzag(6).  %=> 3

Other stuff

small_ints also provides two utility functions which just combine the varint and ZigZag algorithms:

• small_ints:decode_zigzag_varint/1: decodes the next varint from the given binary and then decodes it with ZigZag
• small_ints:encode_zigzag_varint/1: encodes the given integer with ZigZag, then encodes the result with varint

License

MIT License © 2015, Andrea Leopardi