Class: Omnizip::Formats::Rar::Rar5::CRC32

Inherits:
Object
  • Object
show all
Defined in:
lib/omnizip/formats/rar/rar5/crc32.rb

Overview

CRC32 calculation for RAR5 format

Constant Summary collapse

POLYNOMIAL = 
0xEDB88320

Class Method Summary collapse

Class Method Details

.calculate(data) ⇒ Integer

Calculate CRC32 for data

Parameters:

  • data (String) —

    Binary data

Returns:

  • (Integer) —

    32-bit CRC



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# File 'lib/omnizip/formats/rar/rar5/crc32.rb', line 25

def self.calculate(data)
  table = generate_table
  crc = 0xFFFFFFFF

  data.bytes.each do |byte|
    crc = (crc >> 8) ^ table[(crc ^ byte) & 0xFF]
  end

  crc ^ 0xFFFFFFFF
end

.generate_table ⇒ Object

Generate CRC32 lookup table



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# File 'lib/omnizip/formats/rar/rar5/crc32.rb', line 12

def self.generate_table
  @generate_table ||= (0..255).map do |i|
    crc = i
    8.times do
      crc = (crc >> 1) ^ ((crc & 1) * POLYNOMIAL)
    end
    crc
  end
end