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    RE: base64 byte-length formula



    Julian,
    
    The formula in 12-97 is: 
    ((the integer part of)((n+3)*3/4) - m)
    
    Martins formula 3*3/4 where / indictates integer divide.
    
    The encoding of 1 octet in base64 results in 2 characters plus 2 equal
    signs. 
    n=2, m=2.
    
    Martins formula = 2 *3/4 = 1 (truncated to an integer)  right answer
    
    integer part of ((2+3)*3/4)-1 = (integer part of 15/4) - 2 = 3 - 2 = 1 right
    answer
    
    
    The encoding of 2 octets in base64 results in 3 characters plus one equal
    sign. 
    n=3, m=1.
    
    Martins formula = 3 *3/4 = 2 (truncated to an integer)  right answer
    
    integer part of ((3+3)*3/4)-1 = (integer part of 18/4) -1 = 4 - 1 = 3 wrong
    answer
    
    The encoding of 3 octets in base64 results in 4 characters plus no equal
    sign. 
    n=4, m=0.
    
    Martins formula = 4 *3/4 = 3 (truncated to an integer)  right answer
    
    integer part of ((4+3)*3/4)-1 = (integer part of 21/4) -0 = 5 - 1 = 4 wrong
    answer
    
    Pat
    
    -----Original Message-----
    From: Julian Satran [mailto:Julian_Satran@il.ibm.com]
    Sent: Wednesday, June 12, 2002 4:56 PM
    To: Martins Krikis
    Cc: ips@ece.cmu.edu; owner-ips@ece.cmu.edu
    Subject: Re: base64 byte-length formula
    
    
    
    I said already that your formula is correct. 
    I do not understand why you say that the 2 formulas are not equivalent for
    all the lengths (good aor bad)? 
    I would appreciate if you respond although you don't have to. 
    
    Julo 
    
    
    Martins Krikis <mkrikis@yahoo.com> 
    Sent by: owner-ips@ece.cmu.edu 
    06/13/2002 02:34 AM 
    Please respond to Martins Krikis 
            
            To:        Julian Satran/Haifa/IBM@IBMIL 
            cc:        ips@ece.cmu.edu 
            Subject:        Re: base64 byte-length formula 
    
           
    
    
    
    --- Julian Satran <Julian_Satran@il.ibm.com> wrote:
    
    > The difference between our formulas is that I
    > (mistakenly) took 1 digit as 
    > a possible string (or 5, 9 etc.)
    > For those you need the +3 TERM.
    > 
    > For all the good length 2,3,4 6,7,8 etc the two
    > formulas are equivalent.
    
    No they are not. They are only equivalent for
    n = 0 (mod 4). So I'm still insisting that
    n * 3 / 4 is the simplest right formula.
    
    Martins Krikis, Intel Corp.
    
    Disclaimer: these are my opinions and
               may not be Intel's.
    
    
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Last updated: Thu Jun 13 09:18:53 2002
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