Am Mo,04.08.2008 um 14:51 schrieb Jean-Daniel Dupas:
Le 4 août 08 à 13:26, Trygve Inda a écrit :
I am transitioning some code from Carbon to Cocoa and redesigning a
lot of
how things work. I am doing a bit of low-level pixel manipulation and
wondering about speed of access to variables declared in a method
vs those
declared at the object level.
Obviously things like x,y loop counters are local to a method, but
some
things need to be shared between methods and rather then passing
values
around, it would be cleaner to declare these at the object level.
How much of a hit am I going to take?
Would it be best to declare them at the object level and copy it
into a
local as needed... Will the compiler be smart enough to sort this
out?
Will it ever put object (instance) variables in a register?
I know it may require real world testing, but it affects my overall
design
too. Note that it could be going through a loop roughly 3 million
times on a
large image.
Many thanks,
Trygve
IMHO, this is just premature optimisation.
That said, there is no cost to access an ivar using the 32 bits
runtime, and I don't think the cost on 64 bits runtime is important
enough to bother with it.
I agree with this! It is not important how often $something is used,
but which part of all-over costs it produces. If this operation is
done 2389447982374329847239843298 times, the user maybe will wait four
weeks. With a little cost added he will wait four weeks and two hours.
Problem?
On the other hand I'm mnot sure, whether his problem ist really oo. It
sounds a little bit to me, that he makes something oo, which is not
oo. There *can* be advantages to put "compound values" in an object.
But there is no need to do so every time. Sometimes a C-Structure is a
good solution, that works: NSRect, NSPoint …
Amin
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