Class: Cabriolet::Decompressors::Quantum::MSBBitstream

Inherits:
Object
  • Object
show all
Defined in:
lib/cabriolet/decompressors/quantum.rb

Overview

MSB-first bitstream for Quantum (reads 16-bit words MSB first)

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(io_system, handle, buffer_size) ⇒ MSBBitstream

Returns a new instance of MSBBitstream.



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# File 'lib/cabriolet/decompressors/quantum.rb', line 188

def initialize(io_system, handle, buffer_size)
  @io_system = io_system
  @handle = handle
  @buffer_size = buffer_size
  @buffer = ""
  @buffer_pos = 0
  @bit_buffer = 0
  @bits_left = 0
end

Instance Attribute Details

#bits_left ⇒ Object (readonly)

Returns the value of attribute bits_left.



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# File 'lib/cabriolet/decompressors/quantum.rb', line 186

def bits_left
  @bits_left
end

Instance Method Details

#byte_align ⇒ Object 



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# File 'lib/cabriolet/decompressors/quantum.rb', line 226

def byte_align
  @bits_left -= (@bits_left % 8)
end

#read_bits(num_bits) ⇒ Object

Read bits MSB first (matching Quantum’s READ_BITS macro)



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# File 'lib/cabriolet/decompressors/quantum.rb', line 199

def read_bits(num_bits)
  while @bits_left < num_bits
    # Read 16-bit word MSB first
    b0 = read_byte
    b1 = read_byte
    word = (b0 << 8) | b1
    @bit_buffer = (@bit_buffer << 16) | word
    @bits_left += 16
  end

  # Extract bits from MSB side
  @bits_left -= num_bits
  (@bit_buffer >> @bits_left) & ((1 << num_bits) - 1)
end

#read_byte ⇒ Object 



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# File 'lib/cabriolet/decompressors/quantum.rb', line 214

def read_byte
  if @buffer_pos >= @buffer.bytesize
    @buffer = @io_system.read(@handle, @buffer_size)
    @buffer_pos = 0
    return 0 if @buffer.empty?
  end

  byte = @buffer.getbyte(@buffer_pos)
  @buffer_pos += 1
  byte
end