Class: Noyes::GolombRiceEncoder

Inherits:
Object
  • Object
show all
Defined in:
lib/ruby_impl/compression.rb

Overview

Takes disassembled floats and compresses them. We want them dissassembled because compressing exponents and signs have you unique properties and can be efficiently compressed with rice coding. The same is not true of the significand.

Instance Method Summary collapse

Constructor Details

#initialize(m = 8) ⇒ GolombRiceEncoder

Returns a new instance of GolombRiceEncoder.



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# File 'lib/ruby_impl/compression.rb', line 140

def initialize m = 8
  @M = m
  @b = Math.log2(m).to_i
end

Instance Method Details

#<<(data) ⇒ Object

data is a list of disassembled floats



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# File 'lib/ruby_impl/compression.rb', line 146

def << data
  data.map do |b,e,s|
    exp_sign_combo = b |(e << 1)
    [interleave(exp_sign_combo), s]
  end
end

#encode(integer_array) ⇒ Object

Rice encoding returned as a BitArray.



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# File 'lib/ruby_impl/compression.rb', line 161

def encode integer_array
  integer_array = integer_array.clone
  bits = BitArray.new
  integer_array.each do |x|
    q = x/@M
    q.times {bits.push 1}
    bits.push 0
    r = x % @M
    (@b-1).downto(0){|i| bits.push r[i]}
  end
  bits
end

#interleave(x) ⇒ Object

Map negative nubers to odd postive numbers and postive numbers to even positive numbers. We need to do this because negative numbers don’t compress well with rice encoding.



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# File 'lib/ruby_impl/compression.rb', line 156

def interleave x
  x < 0 ? 2 * x.abs - 1 : 2 * x.abs
end