From: Ricardo AF Silva (ricardo.ferreira@mcenergia.com.br)
Date: Mon Jul 31 2006 - 12:30:33 ART
On Monday 31 July 2006 11:14, you wrote:
> Brian,
>
> The math behind XOR is...
> Given the inputs A1 and A2 the output Y is
> Y = ( (NOT A1 AND A2) OR (A1 AND NOT A2) )
>
> Such expression is only true if the inputs are different...
> For three inputs...
>
> Y= ( ( NOT A1 AND NOT A2 AND A3 ) OR ( NOT A1 AND A2 AND NOT A3 ) OR
> ( NOT A1 AND A2 AND A3 ) OR ( A1 AND NOT A2 AND NOT A3 ) OR ( A1 AND NOT A2
> AND A3 ) OR ( A1 AND A2 AND NOT A3 ) )
>
> The expression is true only if the inputs are different...
> That's the beauty under XOR.... To be true only if the inouts are
> different.. no matther the number of them...
> My 0.02
> Ricardo
>
> On Saturday 29 July 2006 19:42, Brian wrote:
> > Brian,
> >
> > Thank you for the clarification.
> >
> > -----Original Message-----
> > From: Brian McGahan [mailto:bmcgahan@internetworkexpert.com]
> > Sent: Saturday, July 29, 2006 3:35 PM
> > To: Brian; Ricardo AF Silva
> > Cc: ccielab@groupstudy.com
> > Subject: RE: XOR for Computing ACL Masks
> >
> > You are correct, XOR does not hold true for an odd number of
> > inputs. I believe the actual logic gate should be:
> >
> > AND(OR(A1,A2, ...An),NOT(AND(A1,A2, ...An)))
> >
> > Where A1 through An are the inputs. The result is that if all
> > inputs are TRUE the result is FALSE, and if all inputs are FALSE the
> > result is FALSE, regardless if there are an even or odd number of
> > inputs. Any other combination results in TRUE. I'll have to revise my
> > document to make this a little clearer; for an odd number of inputs I
> > don't think there is a name for this gate.
> >
> > Thanks for the feedback,
> >
> > Brian McGahan, CCIE #8593
> > bmcgahan@internetworkexpert.com
> >
> > Internetwork Expert, Inc.
> > http://www.InternetworkExpert.com
> > Toll Free: 877-224-8987 x 705
> > Outside US: 775-826-4344 x 705
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> >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> >
> > Of
> >
> > > Brian
> > > Sent: Friday, July 28, 2006 11:06 PM
> > > To: 'Ricardo AF Silva'
> > > Cc: ccielab@groupstudy.com
> > > Subject: RE: XOR for Computing ACL Masks
> > >
> > > I agree with what you have stated and I understand. However this is
> >
> > not
> >
> > > an XOR.
> > >
> > > Brian
> > >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> >
> > Of
> >
> > > Ricardo AF Silva
> > > Sent: Friday, July 28, 2006 10:53 AM
> > > To: Brian
> > > Cc: ccielab@groupstudy.com
> > > Subject: Re: XOR for Computing ACL Masks
> > >
> > > Brian,
> > > I think I got your point so,
> > >
> > > Given two inputs A & B, Xor'ed, the output Y is:
> > >
> > > A B Y
> > > 0 0 0
> > > 0 1 1
> > > 1 0 1
> > > 1 1 0
> > >
> > > For three inputs A, B and C, the output Y is:
> > >
> > > A B C Y
> > > 0 0 0 0
> > > 0 0 1 1
> > > 0 1 0 1
> > > 0 1 1 1
> > > 1 0 0 1
> > > 1 0 1 1
> > > 1 1 0 1
> > > 1 1 1 0
> > >
> > > Conclusion:
> > > the inputs are different ( no matter how many inputs) Y is 1)
> > > the inputs are the same, Y is 0...
> > > That is the logic behind XOR... Look at the inputs and just check if
> >
> > are
> >
> > > equal
> > > or not....
> > >
> > > HTH
> > > Ricardo
> > >
> > > As you can see in the example you have
> > >
> > > On Friday 28 July 2006 13:17, Brian wrote:
> > > > I was using http://mathworld.wolfram.com/XOR.html as a reference. I
> > >
> > > am
> > >
> > > > interested in the specific process (steps) that were used in the
> > > > example.
> > > >
> > > > Brian
> > > >
> > > > -----Original Message-----
> > > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> > >
> > > Of
> > >
> > > > Mienbaikebi Patani
> > > > Sent: Friday, July 28, 2006 9:00 AM
> > > > To: Brian
> > > > Cc: ccielab@groupstudy.com
> > > > Subject: Re: XOR for Computing ACL Masks
> > > >
> > > > I think the XOR works such that u need to have equal number of 0 and
> >
> > 1
> >
> > > > for
> > > > the result to be equal to 1. Anything other than equal number of 0
> >
> > and
> >
> > > 1
> > >
> > > > results in a value equal to 0.
> > > >
> > > > Hope that was informative brother.
> > > >
> > > > On 7/28/06, Brian <briane@surewest.net> wrote:
> > > > > I have been looking at the following example on how to calculate
> >
> > an
> >
> > > > > appropriate mask.
> > > > > http://www.internetworkexpert.com/resources/01700370.htm. While I
> > > > > understand the process that was use (and it works well) I cannot
> > > >
> > > > figure
> > > >
> > > > > out how the mask was calculated using XOR in example 2. If I
> > > >
> > > > understand
> > > >
> > > > > XOR correctly anytime there are an even number of 1's in a
> > >
> > > computation
> > >
> > > > > the result of XOR will be 0. When there are an odd number of 1's
> > >
> > > the
> > >
> > > > > result will be 1. This does not seem to hold true in the example.
> > > > >
> > > > > Can someone please help me understand how XOR was applied to come
> >
> > up
> >
> > > > > with the mask in example 2. Specifically the second octet is
> >
> > where
> >
> > > > the
> > > >
> > > > > confusion comes in. The only conclusions I can draw are that this
> > >
> > > is
> > >
> > > > > not truly an XOR or I do not understand XOR.
> > > > >
> > > > > By the way I tried to XOR 0011 in the MS calculator and the result
> > >
> > > is
> > >
> > > > 0.
> > > >
> > > > > Thanks!
> >
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> > > --
> > > Eng Ricardo Ferreira
> > > CREA 0601395632/D
> >
> > _______________________________________________________________________
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-- Eng Ricardo Ferreira CREA 0601395632/D
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