Class: Cabriolet::Compressors::LZX

Inherits:
Base
  • Object
show all
Defined in:
lib/cabriolet/compressors/lzx.rb

Overview

LZX handles LZX compression Based on libmspack lzxc.c implementation

Phase 1 Implementation:

  • VERBATIM blocks only

  • Basic LZ77 matching

  • Simple tree building

  • No E8 preprocessing

  • 32KB window size

Constant Summary collapse

FRAME_SIZE =

Frame size (32KB per frame)

32_768
BLOCKTYPE_VERBATIM =

Block types

1
BLOCKTYPE_ALIGNED = 
2
BLOCKTYPE_UNCOMPRESSED = 
3
MIN_MATCH =

Match constants

2
MAX_MATCH = 
257
NUM_CHARS = 
256
PRETREE_NUM_ELEMENTS =

Tree constants

20
PRETREE_MAXSYMBOLS = 
20
ALIGNED_NUM_ELEMENTS = 
8
ALIGNED_MAXSYMBOLS = 
8
NUM_PRIMARY_LENGTHS = 
7
NUM_SECONDARY_LENGTHS = 
249
LENGTH_MAXSYMBOLS = 
250
POSITION_SLOTS =

Position slots for different window sizes

[30, 32, 34, 36, 38, 42, 50, 66, 98, 162, 290].freeze
EXTRA_BITS =

Extra bits for position slots

[
  0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8,
  9, 9, 10, 10, 11, 11, 12, 12, 13, 13, 14, 14, 15, 15, 16, 16
].freeze
POSITION_BASE =

Position base offsets

[
  0, 1, 2, 3, 4, 6, 8, 12, 16, 24, 32, 48, 64, 96, 128, 192, 256, 384, 512,
  768, 1024, 1536, 2048, 3072, 4096, 6144, 8192, 12_288, 16_384, 24_576, 32_768,
  49_152, 65_536, 98_304, 131_072, 196_608, 262_144, 393_216, 524_288, 655_360,
  786_432, 917_504, 1_048_576, 1_179_648, 1_310_720, 1_441_792, 1_572_864, 1_703_936,
  1_835_008, 1_966_080, 2_097_152
].freeze

Instance Attribute Summary collapse

Attributes inherited from Base

#buffer_size, #input, #io_system, #output

Instance Method Summary collapse

Constructor Details

#initialize(io_system, input, output, buffer_size, window_bits: 15) ⇒ LZX

Initialize LZX compressor

Parameters:



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# File 'lib/cabriolet/compressors/lzx.rb', line 69

def initialize(io_system, input, output, buffer_size, window_bits: 15)
  super(io_system, input, output, buffer_size)

  # Validate window_bits
  unless (15..21).cover?(window_bits)
    raise ArgumentError,
          "LZX window_bits must be 15-21, got #{window_bits}"
  end

  @window_bits = window_bits
  @window_size = 1 << window_bits

  # Calculate number of position slots
  @num_offsets = POSITION_SLOTS[window_bits - 15] << 3
  @maintree_maxsymbols = NUM_CHARS + @num_offsets

  # Initialize bitstream writer
  @bitstream = Binary::BitstreamWriter.new(io_system, output, buffer_size)

  # Initialize sliding window for LZ77
  @window = "\0" * @window_size
  @window_pos = 0

  # Initialize R0, R1, R2 (LRU offset registers)
  @r0 = 1
  @r1 = 1
  @r2 = 1

  # Statistics for tree building
  @literal_freq = Array.new(NUM_CHARS, 0)
  @match_freq = Array.new(@num_offsets, 0)
  @length_freq = Array.new(LENGTH_MAXSYMBOLS, 0)
end

Instance Attribute Details

#window_bits ⇒ Object (readonly)

Returns the value of attribute window_bits.



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# File 'lib/cabriolet/compressors/lzx.rb', line 60

def window_bits
  @window_bits
end

Instance Method Details

#compress ⇒ Integer

Compress input data using LZX algorithm

Returns:

  • (Integer) —

    Number of bytes written



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# File 'lib/cabriolet/compressors/lzx.rb', line 106

def compress
  input_data = read_all_input
  return 0 if input_data.empty?

  # Write Intel E8 filesize header once at the beginning (1 bit = 0, meaning no E8 processing)
  @bitstream.write_bits(0, 1)

  total_compressed = 0
  pos = 0

  # Process data in FRAME_SIZE chunks
  while pos < input_data.bytesize
    frame_size = [FRAME_SIZE, input_data.bytesize - pos].min
    frame_data = input_data[pos, frame_size]

    # Compress this frame
    compress_frame(frame_data)

    pos += frame_size
    total_compressed += frame_size
  end

  # Flush any remaining bits
  @bitstream.flush

  total_compressed
end