Class: Omnizip::Formats::Rar::Rar5::Compression::Lzss::BitReader

Inherits:
Object
  • Object
show all
Defined in:
lib/omnizip/formats/rar/rar5/compression/lzss.rb

Overview

Bit reader for reading individual bits from compressed data

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(data) ⇒ BitReader

Returns a new instance of BitReader.



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# File 'lib/omnizip/formats/rar/rar5/compression/lzss.rb', line 122

def initialize(data)
  @data = data
  @byte_pos = 0
  @bit_pos = 0
end

Instance Attribute Details

#bit_pos ⇒ Object

Returns the value of attribute bit_pos.



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# File 'lib/omnizip/formats/rar/rar5/compression/lzss.rb', line 201

def bit_pos
  @bit_pos
end

#byte_pos ⇒ Object

Returns the value of attribute byte_pos.



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# File 'lib/omnizip/formats/rar/rar5/compression/lzss.rb', line 201

def byte_pos
  @byte_pos
end

Instance Method Details

#end_of_data?(block_size) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/omnizip/formats/rar/rar5/compression/lzss.rb', line 197

def end_of_data?(block_size)
  @byte_pos >= block_size || (@byte_pos == block_size - 1 && @bit_pos >= 8)
end

#read_bits(num_bits) ⇒ Object

Read up to 16 bits



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# File 'lib/omnizip/formats/rar/rar5/compression/lzss.rb', line 129

def read_bits(num_bits)
  return 0 if num_bits.zero?

  result = 0
  bits_read = 0

  while bits_read < num_bits
    return nil if @byte_pos >= @data.bytesize

    byte = @data.getbyte(@byte_pos)
    bits_available = 8 - @bit_pos
    bits_needed = num_bits - bits_read
    bits_to_read = [bits_available, bits_needed].min

    mask = ((1 << bits_to_read) - 1) << @bit_pos
    bits = (byte & mask) >> @bit_pos

    result |= bits << bits_read
    bits_read += bits_to_read
    @bit_pos += bits_to_read

    if @bit_pos >= 8
      @bit_pos = 0
      @byte_pos += 1
    end
  end

  result
end

#read_bits_32(num_bits) ⇒ Object

Read 32 bits



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# File 'lib/omnizip/formats/rar/rar5/compression/lzss.rb', line 169

def read_bits_32(num_bits)
  return 0 if num_bits.zero?

  result = 0
  bits_read = 0

  while bits_read < num_bits && @byte_pos < @data.bytesize
    byte = @data.getbyte(@byte_pos)
    bits_available = 8 - @bit_pos
    bits_needed = num_bits - bits_read
    bits_to_read = [bits_available, bits_needed].min

    mask = ((1 << bits_to_read) - 1) << @bit_pos
    bits = (byte & mask) >> @bit_pos

    result |= bits << bits_read
    bits_read += bits_to_read
    @bit_pos += bits_to_read

    if @bit_pos >= 8
      @bit_pos = 0
      @byte_pos += 1
    end
  end

  result
end

#skip_bits(num_bits) ⇒ Object

Skip specified number of bits



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# File 'lib/omnizip/formats/rar/rar5/compression/lzss.rb', line 160

def skip_bits(num_bits)
  @bit_pos += num_bits
  while @bit_pos >= 8
    @bit_pos -= 8
    @byte_pos += 1
  end
end