Class: Cabriolet::Compressors::MSZIP

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

Overview

MSZIP handles MSZIP (DEFLATE) compression Based on RFC 1951 and libmspack implementation

Constant Summary collapse

FRAME_SIZE =

MSZIP frame size (32KB sliding window)

32_768
SIGNATURE =

MSZIP signature bytes

[0x43, 0x4B].freeze
STORED_BLOCK =

Block types

0
FIXED_HUFFMAN_BLOCK = 
1
DYNAMIC_HUFFMAN_BLOCK = 
2
MIN_MATCH =

Match length constants

3
MAX_MATCH = 
258
WINDOW_SIZE =

Window size for LZ77

32_768
LIT_LENGTHS =

Match lengths for literal codes 257-285

[
  3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27,
  31, 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258
].freeze
DIST_OFFSETS =

Match offsets for distance codes 0-29

[
  1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193, 257, 385,
  513, 769, 1025, 1537, 2049, 3073, 4097, 6145, 8193, 12_289, 16_385, 24_577
].freeze
LIT_EXTRABITS =

Extra bits for literal codes 257-285

[
  0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2,
  2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 0
].freeze
DIST_EXTRABITS =

Extra bits for distance codes 0-29

[
  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
].freeze

Instance Attribute Summary

Attributes inherited from Base

#buffer_size, #input, #io_system, #output

Instance Method Summary collapse

Constructor Details

#initialize(io_system, input, output, buffer_size) ⇒ MSZIP

Initialize MSZIP compressor

Parameters:



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# File 'lib/cabriolet/compressors/mszip.rb', line 59

def initialize(io_system, input, output, buffer_size)
  super

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

  # Build fixed Huffman codes
  @fixed_codes = Huffman::Encoder.build_fixed_codes

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

Instance Method Details

#compress ⇒ Integer

Compress input data using MSZIP (DEFLATE) algorithm

Returns:

  • (Integer) —

    Number of bytes written



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# File 'lib/cabriolet/compressors/mszip.rb', line 76

def compress
  input_data = read_all_input
  total_written = 0
  pos = 0

  # Handle empty input - still need to write a block
  if input_data.empty?
    write_signature
    compress_block("", true)
    @bitstream.flush
    return 0
  end

  # Process data in FRAME_SIZE chunks
  # Each frame is independent and contains blocks ending with last_block=1
  while pos < input_data.bytesize
    chunk_size = [FRAME_SIZE, input_data.bytesize - pos].min
    chunk = input_data[pos, chunk_size]

    # Write CK signature
    write_signature

    # Compress block with fixed Huffman
    # Each frame's block is always marked as last within that frame
    compress_block(chunk, true)

    pos += chunk_size
    total_written += chunk_size
  end

  # Flush any remaining bits
  @bitstream.flush

  total_written
end