RE: base64 byte-length formula

["Julian Satran" <Julian_Satran@il.ibm.com>]

Pat,

I think you are talking about the formula in 12-96 and I am talking about the one in 12-98.
Martins formula and mine are equivalent for good encodings.
As I said I made it up only to account for encodings that are in fact impossible - like 1, 4 ... 4*n+1 base 64 digits.
And I will  put in Martins formula with a note about the impossible numbers.
Can we stop this thread?

Julo

pat_thaler@agilent.com 06/13/2002 03:33 AM Please respond to pat_thaler

To:        Julian Satran/Haifa/IBM@IBMIL, mkrikis@yahoo.com         cc:        ips@ece.cmu.edu, owner-ips@ece.cmu.edu         Subject:        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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