Simple question - (If Not A = B Then... ) vs ( If A <> B Then...)

[Rhudi]

Which is better?

If Not A = B Then...
-OR-
If A <> B Then...

They are logically identical, right? But, which one uses less memory/cpu cycles/quantum foam/etc?

[walruseggman]

Use Timer and see if you can tell the difference. I would be surprised if there is any actual difference at all, though.

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[Rhudi]

I bet you a nickle that if there is a difference, it might be measurable in nano-seconds. I'm OCD enough, that I'm talking CPU clock cycles.

[walruseggman]

So was there a difference with Timer?

[Rhudi]

The code this question came up in is way more complex than this simple question. :P

I enjoy deep logical conundrums. Things like, "If Not ( A Or B )" is logically identical to "If Not A And Not B". Readability would dictate which way I write it, but I was curious as to which was more CPU-friendly.

[StephenR]

I suppose the obvious thing would be to use the Timer on your actual code, report back and put us out of our misery.

[Rhudi]

Unfortunately, I believe that anything that I could try with timer would only give me a subjective answer that couldn't answer the deeper question.
I started thinking about this by reading here: http://www.ozgrid.com/VBA/SpeedingUpVBACode.htm
Perhaps I can ask there.

[Pete_UK]

Not is a logical operation, whereas <> can also apply to strings, numbers etc. If A and B are Boolean, then it will be quicker to use Not as that is a simple inversion of bits. Using IF is likely to take many more CPU cycles, however, as that is much more processor-intensive.

Hope this helps.

Pete

[kalak]

'fraid it's not very clear to me just what you consider a "subjective answer" in this context
nor what actually is the "deeper question"
perhaps could you be more specific? do I assume your question is practical (say concerning computer capacity) or just of theoretical interest?

regarding your opening post and the comments about timer in the thread, a simple coded example may give some clues
change the red line to your "logically identical" version and note the difference
there is a difference with my computer, 1.93 secs with the Not = and 1.19 secs with the <> (which is 62% time difference)

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[Norie]

They aren't logically equivalent..

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[Rhudi]

My dad bought me a logic game called "wyff-n-proof" when I was 12. That taught me logical operators.

Regardless of what A and B are (bool, str, int, etc); if they are equal or not equal, logic will answer the if/then.
If A(of any type) = B(of the same type) Then (whatever).
If A <> B Then (whatever).
If Not(A = B) Then (whatever).
The last two are logically identical.


Rules get really odd, when you are doing boolean compares:
If Not A Or Not B Then... does one thing.
If Not (A And B) Then ... does the same thing.
You can prove this with a Karnaugh Map:
http://en.wikipedia.org/wiki/Karnaugh_map

( cross post: http://www.ozgrid.com/forum/newreply...reply&t=192068 )