Class: Digest::CRC16QT

Inherits:
CRC16CCITT show all
Defined in:
lib/digest/crc16_qt.rb

Overview

Implements the CRC16_CCITT algorithm used in QT algorithms.

Author:

  • Matthew Bednarski

Constant Summary collapse

FINAL_XOR = 
0xffff
REVERSE_CRC_RESULT = 
true
REVERSE_DATA = 
true

Constants inherited from CRC16CCITT

Digest::CRC16CCITT::INIT_CRC, Digest::CRC16CCITT::TABLE

Constants inherited from CRC16

Digest::CRC16::INIT_CRC, Digest::CRC16::TABLE, Digest::CRC16::WIDTH

Constants inherited from CRC

Digest::CRC::INIT_CRC, Digest::CRC::WIDTH, Digest::CRC::XOR_MASK

Instance Method Summary collapse

Methods inherited from CRC16

pack

Methods inherited from CRC

#<<, #block_length, checksum, #digest_length, #finish, #initialize, pack, #reset

Constructor Details

This class inherits a constructor from Digest::CRC

Instance Method Details

#checksum ⇒ Object 



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# File 'lib/digest/crc16_qt.rb', line 31

def checksum
  crc = @crc + 0
  crc ^= FINAL_XOR      if FINAL_XOR
  crc = revert_bits crc if REVERSE_CRC_RESULT
  return crc
end

#revert_bits(cc) ⇒ Object (protected) 



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# File 'lib/digest/crc16_qt.rb', line 40

def revert_bits(cc)
  ob = 0
  b  = (1 << 15)

  16.times do |t|
    ob |= (1 << t) if (cc & b) != 0
    b >>= 1
  end

  return ob
end

#revert_byte(cc) ⇒ Object (protected) 



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# File 'lib/digest/crc16_qt.rb', line 52

def revert_byte(cc)
  ob = 0
  b  = (1 << 7)

  8.times do |t|
    ob |= (1 << t) if (cc & b) != 0
    b >>= 1
  end

  return ob
end

#update(data) ⇒ Object

Updates the CRC16 checksum.

Parameters:

  • data (String) —

    The data to update the checksum with.



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# File 'lib/digest/crc16_qt.rb', line 22

def update(data)
  data.each_byte do |b|
    b = revert_byte(b) if REVERSE_DATA
    @crc = ((TABLE[((@crc >> 8) ^ b) & 0xff] ^ (@crc << 8)) & 0xffff)
  end

  return self
end