Check Sum

[Bill Marriott]

Rev has the function md5digest; you could take the last digit of that; but 
from a processing point of view it might be overkill.

I looked up "check digit" in Wikipedia. It seems one popular check digit is 
"UPC." From Wikipedia:

>>>
The final digit of a Universal Product Code is a check digit computed as 
follows:

1. Add the digits in the odd-numbered positions (first, third, fifth, etc.) 
together and multiply by three.
2. Add the digits in the even-numbered positions (second, fourth, sixth, 
etc.) to the result.
3. Subtract the result from the next-higher multiple of ten. The answer is 
the check digit.

For instance, a UPC-A barcode (In this case, a UPC for a box of tissues) 
"03600029145X" where X is the check digit, X can be calculated by adding the 
odd-numbered digits (0+6+0+2+1+5 = 14), multiplying by three (14 × 3 = 42), 
adding the even-numbered digits (42+3+0+0+9+4 = 58) and subtracting from the 
next-highest multiple of ten (60 - 58 = 2). The check digit is thus 2.
<<<

function upcCheck pValue
  repeat with i = 1 to the length of pValue step 2
    add char i of pValue to x
  end repeat
  multiply x by 3
  repeat with i = 2 to the length of pValue step 2
    add char i of pValue to x
  end repeat

  return 10 - ( x mod 10 )
end upcCheck



"Scott Kane" <scott at cdroo.com> wrote in 
message news:019801c78596$6128c940$0201010a at esbgdi9s3atqpx...
> Hi people,
>
> Been reading some of the great scripts online for Rev for encryption and 
> hashing etc.  One thing I've not been able to find (checked the doc's) is 
> a method to generate (and check) a check digit.  I can do this in assembly 
> just fine (not much use in Rev unless I code an external which for 
> security reasons I don't want to do).  Is there a method I've missed that 
> would allow a number (hex aware preferably) that allows one to do this?
>
> Note that the results I manage to glean for this will be published in an 
> article for the Revolution newsletter in regards to license systems and 
> anti piracy measures.  I have a system in Delphi and C++ that I wish to 
> translate into Rev and then share the results within that article 
> (including code).
>
> Scott
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