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 66

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
  when 'OpenC3::Crc16'
    @bit_size = 16
    pack = 'S'
    filter_mask = 0xFFFF
  when 'OpenC3::Crc32'
    @bit_size = 32
    pack = 'I'
    filter_mask = 0xFFFFFFFF
  when 'OpenC3::Crc64'
    @bit_size = 64
    pack = 'Q'
    filter_mask = 0xFFFFFFFFFFFFFFFF
  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
  end
end

Instance Attribute Details

#poly ⇒ Integer (readonly)

Returns The polynomial used when calcuating the CRC.

Returns:

  • (Integer) —

    The polynomial used when calcuating the CRC



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# File 'lib/openc3/utilities/crc.rb', line 49

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 55

def reflect
  @reflect
end

#seed ⇒ Integer (readonly)

Returns Seed value used to start the calulation.

Returns:

  • (Integer) —

    Seed value used to start the calulation



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# File 'lib/openc3/utilities/crc.rb', line 51

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 57

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 53

def xor
  @xor
end

Instance Method Details

#bit_reverse_16(value) ⇒ Object 



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# File 'lib/openc3/utilities/crc.rb', line 123

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 128

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 135

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 119

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 107