From: Paul Golea <uddunneso_224@...>
Date: 2009-02-23T18:44:24+09:00
Subject: Cyclic redundancy check (CRC32) of a file

Hello,

I try to calculate the CRC32 of a file with a script ruby, but I does
not obtain the good result by comparison with many of the other software
which already make this (in other programming language...), for example:
http://www.codeproject.com/KB/recipes/crc32.aspx

I use this script :
_____________________

require 'zlib'
filetest = File.read 'image.jpg'
puts Zlib.crc32(filetest, 0).to_s(16).upcase
_____________________

The result looks like well of an CRC32 but it is never good...

I also try a pure ruby implementation with this code but it makes
exactly the zlib.crc32 result... :
_____________________

def crc32(c)
    n = c.length
    r = 0xFFFFFFFF
    n.times do |i|
        r ^= c[i]
        8.times do
            if (r & 1)!=0
                r = (r>>1) ^ 0xEDB88320
            else
                r >>= 1
            end
        end
    end
    r ^ 0xFFFFFFFF
end

filetest = File.read 'image.jpg'
puts crc32(filetest).to_s(16).upcase
_____________________


Thank you very much to the person who will have the solution of my
problem.
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