"Synchsafe" Integers

"Synchsafe" integers are defined by section 6.2 of the ID3 standard structure as follows:

Synchsafe integers are integers that keep its highest bit (bit 7) zeroed, making seven bits out of eight available. Thus a 32 bit synchsafe integer can store 28 bits of information.

The spec then provides a single example:

   Example:
     255 (%11111111) encoded as a 16 bit synchsafe integer is 383
     (%00000001 01111111).

This is, of course, a huge pain in the ass, so I hope this implementation will help someone else not have to deal with this headache.

Installation

1. Add the dependency to your shard.yml:

   dependencies:
     synchsafe_integer:
       github: dscottboggs/synchsafe_integer.cr
   

2. Run shards install

Usage

require "synchsafe_integer"

puts 255.synchsafe_encode # => 383
puts 383.synchsafe_decode # => 255

An error is thrown at run-time if the number is larger than 28 bits when encoding, or contains any bytes with the 7th (high) bit set to 1 when decoding.

Contributing

1. Fork it (https://github.com/dscottboggs/synchsafe_integer.cr/fork)
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Contributors

• D. Scott Boggs - creator and maintainer