Class: Rbimg::Strategies::CRCTableLookup

Inherits:
Object
  • Object
show all
Defined in:
lib/strategies/crc_strategies/crc_table_lookup_strategy.rb

Constant Summary collapse

@@crc_table = 
{}

Class Method Summary collapse

Class Method Details

.crc(type, data) ⇒ Object 



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# File 'lib/strategies/crc_strategies/crc_table_lookup_strategy.rb', line 25

def self.crc(type, data)
    c = ([255] * 4).pack("C4").unpack("L").first
    buff = type + data
    make_crc_table if !crc_table_computed
    for n in 0...buff.length
        c = @@crc_table[(c ^ buff[n]) & 255] ^ (c >> 8)
    end
    Byteman.int2buf(c ^ Byteman.buf2int([255] * 4))
end

.crc_table_computed ⇒ Object 



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# File 'lib/strategies/crc_strategies/crc_table_lookup_strategy.rb', line 19

def self.crc_table_computed
    @@crc_table.length > 0
end

.make_crc_table ⇒ Object 



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# File 'lib/strategies/crc_strategies/crc_table_lookup_strategy.rb', line 5

def self.make_crc_table
    for n in 0...256
        c = n
        for k in 0...8
            if c.odd? 
                c = 3988292384 ^ (c >> 1)
            else
                c = c >> 1
            end
        end
        @@crc_table[n] = c
    end
end