Class: HexaPDF::Utils::BitStreamReader

Inherits:
Object
  • Object
show all
Defined in:
lib/hexapdf/utils/bit_stream.rb

Overview

Helper class for reading variable length integers from a bit stream.

This class allows one to read integers with a variable width from a bit stream using the #read method. The data from where these bits are read, can be set on intialization and additional data can later be appended.

Instance Method Summary collapse

Constructor Details

#initialize(data = +'')) ⇒ BitStreamReader

Creates a new object, optionally providing the string from where the bits should be read.



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# File 'lib/hexapdf/utils/bit_stream.rb', line 50

def initialize(data = +'')
  @data = data.force_encoding(Encoding::BINARY)
  @pos = 0
  @bit_cache = 0
  @available_bits = 0
end

Instance Method Details

#append_data(str) ⇒ Object Also known as: <<

Appends some data to the string from where bits are read.



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# File 'lib/hexapdf/utils/bit_stream.rb', line 58

def append_data(str)
  @data.slice!(0, @pos)
  @data << str
  @pos = 0
  self
end

#read(bits) ⇒ Object

Reads bits number of bits.

Returns nil if not enough bits are available for reading.



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# File 'lib/hexapdf/utils/bit_stream.rb', line 79

def read(bits)
  while @available_bits < bits
    @bit_cache = (@bit_cache << 8) | (@data.getbyte(@pos) || return)
    @pos += 1
    @available_bits += 8
  end
  @available_bits -= bits
  result = (@bit_cache >> @available_bits)
  @bit_cache &= (1 << @available_bits) - 1
  result
end

#read?(bits) ⇒ Boolean

Returns true if bits number of bits can be read.

Returns:

  • (Boolean) 


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# File 'lib/hexapdf/utils/bit_stream.rb', line 72

def read?(bits)
  remaining_bits >= bits
end

#remaining_bits ⇒ Object

Returns the number of remaining bits that can be read.



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# File 'lib/hexapdf/utils/bit_stream.rb', line 67

def remaining_bits
  (@data.length - @pos) * 8 + @available_bits
end