Module: Cabriolet::Checksum

Defined in:
lib/cabriolet/checksum.rb

Overview

Utility module for checksum calculations

Class Method Summary collapse

Class Method Details

.calculate(data, initial = 0) ⇒ Integer

Calculate CAB-style checksum (XOR-based)

Parameters:

  • data (String) —

    Data to calculate checksum for

  • initial (Integer) (defaults to: 0) —

    Initial checksum value (default: 0)

Returns:

  • (Integer) —

    Checksum value (32-bit)



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# File 'lib/cabriolet/checksum.rb', line 11

def self.calculate(data, initial = 0)
  cksum = initial
  bytes = data.bytes

  # Process 4-byte chunks
  (bytes.size / 4).times do |i|
    offset = i * 4
    value = bytes[offset] |
      (bytes[offset + 1] << 8) |
      (bytes[offset + 2] << 16) |
      (bytes[offset + 3] << 24)
    cksum ^= value
  end

  # Process remaining bytes
  remainder = bytes.size % 4
  if remainder.positive?
    ul = 0
    offset = bytes.size - remainder

    case remainder
    when 3
      ul |= bytes[offset + 2] << 16
      ul |= bytes[offset + 1] << 8
      ul |= bytes[offset]
    when 2
      ul |= bytes[offset + 1] << 8
      ul |= bytes[offset]
    when 1
      ul |= bytes[offset]
    end

    cksum ^= ul
  end

  cksum & 0xFFFFFFFF
end