Steven Sacks | BLITZ wrote:
It's the fastest because:
Pre-decrementation (--i) is faster than post-decrementation (i--)
I don't see why that would be. Both "var i=1;i--;" and "var i=1;--i;"
compile down to the exact same 8 lines of p-code:
_constantPool "i"
_push "i" 1
_var
_push "i" "i"
_getVariable
_decrement
_setVariable
_end
So i don't see how one can be faster than the other. Maybe in other
languages this is the case?
And substraction (- (-1) is faster than addition (+ 1).
I ran numerous tests using loops of 1 million on this but was unable to
conclude one way or the other because roughly half the time one method
was faster than the other. differences ranged from 1 millisecond to 175
milliseconds in both directions. My only take on my results is that
they are at least negligably similar.
They are faster because it's less code that gets produced when you
compile.
http://flasm.sourceforge.net/#optimization
This isn't true. (i--) is one less line of p-code (and 9 less bytes of
data) than (--i -(-1)) because it isn't doing the extra calculation of
subtraction like I mentioned in my email. Take a look at the p-code:
var i:Number = 1;
while (i--) {
trace(i);
}
_constantPool "i"
_push "i" 1
_var
#4 _push "i"
_getVariable
_push "i" "i"
_getVariable
_decrement
_setVariable
_not
_if true goto #16
_push "i"
_getVariable
_trace
_jump to #4
#16 _end
------------------------------
var i:Number = 1;
while (--i -(-1)) {
trace(i);
}
_constantPool "i"
_push "i" 1
_var
#4 _push "i" "i"
_getVariable
_decrement
_storeRegister 0
_setVariable
_push register0 4294967295
_subtract
_not
_if true goto #17
_push "i"
_getVariable
_trace
_jump to #4
#17 _end
For most cases, it's a matter of milliseconds or even less, which isn't
that big a deal, but I use it anyway because it's a good habit to have
and it makes my code logic work with that in mind always so when it does
make a difference in seconds, it's already there.
I agree about it not being a big deal, but I prefer the (i--) method
over (--i -(-1)) since I find it easier to read.
-- James
James O'Reilly
www.jamesor.com
_______________________________________________
[email protected]
To change your subscription options or search the archive:
http://chattyfig.figleaf.com/mailman/listinfo/flashcoders
Brought to you by Fig Leaf Software
Premier Authorized Adobe Consulting and Training
http://www.figleaf.com
http://training.figleaf.com
