Class: OpenC3::Crc

Inherits:
Object show all
Defined in:
lib/openc3/utilities/crc.rb,
ext/openc3/ext/crc/crc.c

Overview

Abstract base class which Crc16, Crc32 and Crc64 use. Do NOT use this class directly but instead use one of the subclasses.

Direct Known Subclasses

Crc16, Crc32, Crc64, Crc8

Constant Summary collapse

BIT_REVERSE_TABLE = 
[
  0x00, 0x80, 0x40, 0xC0, 0x20, 0xA0, 0x60, 0xE0, 0x10, 0x90, 0x50, 0xD0, 0x30, 0xB0, 0x70, 0xF0,
  0x08, 0x88, 0x48, 0xC8, 0x28, 0xA8, 0x68, 0xE8, 0x18, 0x98, 0x58, 0xD8, 0x38, 0xB8, 0x78, 0xF8,
  0x04, 0x84, 0x44, 0xC4, 0x24, 0xA4, 0x64, 0xE4, 0x14, 0x94, 0x54, 0xD4, 0x34, 0xB4, 0x74, 0xF4,
  0x0C, 0x8C, 0x4C, 0xCC, 0x2C, 0xAC, 0x6C, 0xEC, 0x1C, 0x9C, 0x5C, 0xDC, 0x3C, 0xBC, 0x7C, 0xFC,
  0x02, 0x82, 0x42, 0xC2, 0x22, 0xA2, 0x62, 0xE2, 0x12, 0x92, 0x52, 0xD2, 0x32, 0xB2, 0x72, 0xF2,
  0x0A, 0x8A, 0x4A, 0xCA, 0x2A, 0xAA, 0x6A, 0xEA, 0x1A, 0x9A, 0x5A, 0xDA, 0x3A, 0xBA, 0x7A, 0xFA,
  0x06, 0x86, 0x46, 0xC6, 0x26, 0xA6, 0x66, 0xE6, 0x16, 0x96, 0x56, 0xD6, 0x36, 0xB6, 0x76, 0xF6,
  0x0E, 0x8E, 0x4E, 0xCE, 0x2E, 0xAE, 0x6E, 0xEE, 0x1E, 0x9E, 0x5E, 0xDE, 0x3E, 0xBE, 0x7E, 0xFE,
  0x01, 0x81, 0x41, 0xC1, 0x21, 0xA1, 0x61, 0xE1, 0x11, 0x91, 0x51, 0xD1, 0x31, 0xB1, 0x71, 0xF1,
  0x09, 0x89, 0x49, 0xC9, 0x29, 0xA9, 0x69, 0xE9, 0x19, 0x99, 0x59, 0xD9, 0x39, 0xB9, 0x79, 0xF9,
  0x05, 0x85, 0x45, 0xC5, 0x25, 0xA5, 0x65, 0xE5, 0x15, 0x95, 0x55, 0xD5, 0x35, 0xB5, 0x75, 0xF5,
  0x0D, 0x8D, 0x4D, 0xCD, 0x2D, 0xAD, 0x6D, 0xED, 0x1D, 0x9D, 0x5D, 0xDD, 0x3D, 0xBD, 0x7D, 0xFD,
  0x03, 0x83, 0x43, 0xC3, 0x23, 0xA3, 0x63, 0xE3, 0x13, 0x93, 0x53, 0xD3, 0x33, 0xB3, 0x73, 0xF3,
  0x0B, 0x8B, 0x4B, 0xCB, 0x2B, 0xAB, 0x6B, 0xEB, 0x1B, 0x9B, 0x5B, 0xDB, 0x3B, 0xBB, 0x7B, 0xFB,
  0x07, 0x87, 0x47, 0xC7, 0x27, 0xA7, 0x67, 0xE7, 0x17, 0x97, 0x57, 0xD7, 0x37, 0xB7, 0x77, 0xF7,
  0x0F, 0x8F, 0x4F, 0xCF, 0x2F, 0xAF, 0x6F, 0xEF, 0x1F, 0x9F, 0x5F, 0xDF, 0x3F, 0xBF, 0x7F, 0xFF
]

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(poly, seed, xor, reflect) ⇒ Crc

Creates a CRC algorithm instance.

Parameters:

  • poly (Integer) —

    Polynomial to use when calculating the CRC

  • seed (Integer) —

    Seed value to start the calculation

  • xor (Boolean) —

    Whether to XOR the CRC result with 0xFFFF

  • reflect (Boolean) —

    Whether to bit reverse each byte of data before calculating the CRC



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# File 'lib/openc3/utilities/crc.rb', line 61

def initialize(poly, seed, xor, reflect)
  @poly = poly
  @seed = seed
  @xor = xor
  @reflect = reflect
  if RUBY_ENGINE == 'ruby' and !ENV['OPENC3_NO_EXT']
    @table = ''
  else
    @table = []
  end

  # Determine which class we're using: Crc8, Crc16, Crc32, Crc64
  case self.class.name
  when 'OpenC3::Crc8'
    @bit_size = 8
    pack = 'C'
    filter_mask = 0xFF
    right_shift = 0
  when 'OpenC3::Crc16'
    @bit_size = 16
    pack = 'S'
    filter_mask = 0xFFFF
    right_shift = 8
  when 'OpenC3::Crc32'
    @bit_size = 32
    pack = 'I'
    filter_mask = 0xFFFFFFFF
    right_shift = 24
  when 'OpenC3::Crc64'
    @bit_size = 64
    pack = 'Q'
    filter_mask = 0xFFFFFFFFFFFFFFFF
    right_shift = 56
  end
  if RUBY_ENGINE == 'ruby' and !ENV['OPENC3_NO_EXT']
    (0..255).each do |index|
      @table << [compute_table_entry(index, @bit_size)].pack(pack)
    end
  else
    (0..255).each do |index|
      @table << (compute_table_entry(index, @bit_size) & filter_mask)
    end

    @filter_mask = filter_mask
    @right_shift = right_shift
    @bit_reverse = method("bit_reverse_#{@bit_size}")

    # A reflected (least-significant-bit first) table avoids reversing each
    # input byte in calc. CRC32 and CRC64 get three additional tables so
    # their common reflected forms can process four bytes per Ruby loop.
    if @reflect
      reflected_table = Array.new(256) do |index|
        @bit_reverse.call(@table[BIT_REVERSE_TABLE[index]])
      end
      @reflected_tables = [reflected_table]
      if @bit_size >= 32
        3.times do
          previous_table = @reflected_tables[-1]
          @reflected_tables << Array.new(256) do |index|
            value = previous_table[index]
            (value >> 8) ^ reflected_table[value & 0xFF]
          end
        end
      end
    end
  end
end

Instance Attribute Details

#poly ⇒ Integer (readonly)

Returns The polynomial used when calculating the CRC.

Returns:

  • (Integer) —

    The polynomial used when calculating the CRC



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# File 'lib/openc3/utilities/crc.rb', line 44

def poly
  @poly
end

#reflect ⇒ Boolean (readonly)

Returns Whether to bit reverse each byte.

Returns:

  • (Boolean) —

    Whether to bit reverse each byte



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# File 'lib/openc3/utilities/crc.rb', line 50

def reflect
  @reflect
end

#seed ⇒ Integer (readonly)

Returns Seed value used to start the calculation.

Returns:

  • (Integer) —

    Seed value used to start the calculation



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# File 'lib/openc3/utilities/crc.rb', line 46

def seed
  @seed
end

#table ⇒ String (readonly)

Returns Binary lookup table used to perform the calculation.

Returns:

  • (String) —

    Binary lookup table used to perform the calculation



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# File 'lib/openc3/utilities/crc.rb', line 52

def table
  @table
end

#xor ⇒ Boolean (readonly)

Returns Whether the result is XORed with 0xFFFF.

Returns:

  • (Boolean) —

    Whether the result is XORed with 0xFFFF



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# File 'lib/openc3/utilities/crc.rb', line 48

def xor
  @xor
end

Instance Method Details

#bit_reverse_16(value) ⇒ Object 



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# File 'lib/openc3/utilities/crc.rb', line 145

def bit_reverse_16(value)
  (BIT_REVERSE_TABLE[value & 0xFF] << 8) |
    (BIT_REVERSE_TABLE[(value >> 8) & 0xFF])
end

#bit_reverse_32(value) ⇒ Object 



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# File 'lib/openc3/utilities/crc.rb', line 150

def bit_reverse_32(value)
  (BIT_REVERSE_TABLE[value & 0xFF] << 24) |
    (BIT_REVERSE_TABLE[(value >> 8) & 0xFF] << 16) |
    (BIT_REVERSE_TABLE[(value >> 16) & 0xFF] << 8) |
    (BIT_REVERSE_TABLE[(value >> 24) & 0xFF])
end

#bit_reverse_64(value) ⇒ Object 



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# File 'lib/openc3/utilities/crc.rb', line 157

def bit_reverse_64(value)
  (BIT_REVERSE_TABLE[value & 0x00000000000000FF] << 56) |
    (BIT_REVERSE_TABLE[(value >> 8) & 0x00000000000000FF] << 48) |
    (BIT_REVERSE_TABLE[(value >> 16) & 0x00000000000000FF] << 40) |
    (BIT_REVERSE_TABLE[(value >> 24) & 0x00000000000000FF] << 32) |
    (BIT_REVERSE_TABLE[(value >> 32) & 0x00000000000000FF] << 24) |
    (BIT_REVERSE_TABLE[(value >> 40) & 0x00000000000000FF] << 16) |
    (BIT_REVERSE_TABLE[(value >> 48) & 0x00000000000000FF] << 8) |
    (BIT_REVERSE_TABLE[(value >> 56) & 0x00000000000000FF])
end

#bit_reverse_8(value) ⇒ Integer

Bit reverse the 8 bit value

Parameters:

  • value (Integer)

Returns:

  • (Integer) —

    Bit reversed value



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# File 'lib/openc3/utilities/crc.rb', line 141

def bit_reverse_8(value)
  BIT_REVERSE_TABLE[value & 0xFF]
end

#calc(data, seed = @seed) ⇒ Integer

Calculates the CRC across the data buffer using the optional seed. Implemented in C for speed.

Parameters:

  • data (String) —

    String buffer of binary data to calculate a CRC on

  • seed (Integer|nil) (defaults to: @seed) —

    Seed value to start the calculation. Pass nil to use the default seed set in the constructor.

Returns:

  • (Integer) —

    The CRC value




# File 'lib/openc3/utilities/crc.rb', line 129