RE: VC.NET 'Optimization'

Perhaps I missed something earlier on since I haven't been following
this thread that closely, but I don't see your point.  Looking at the
two code statements quoted:

	timer.Restart();
	printf( "time=%f, result=%d\n", timer.GetElapsed(),
fibonacci(42));

The compiler could call the functions in this order:

	timer.Restart()
	timer.GetElapsed()
	fibonacci()
	printf()

Or it could call them in this order:

	timer.Restart()
	fibonacci()
	timer.GetElapsed()
	printf()

Only the latter one would have the timer include the fibonacci() call
time, because it's made between the timer.Restart() and
timer.GetElapsed().

To be safe, as you said, the fibonacci() call would have to be made in a
statement after the timer.Restart() but before the printf() containing
the timer.GetElapsed();

j

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
Lewin, Gareth
Sent: Tuesday, April 12, 2005 4:12 PM
To: [email protected]
Subject: RE: [GD-Windows] VC.NET 'Optimization'

Again, the order doesn't matter, the fib function has no side effects.

His goal in this specific case is to measure the speed of his fib
function, so contextually changing the order the params are passed will
work.

If the order mattered, then fib would have been called outside the
printf scope. 

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
Grills, Jeff
Sent: Tuesday, April 12, 2005 12:17 PM
To: [email protected]
Subject: RE: [GD-Windows] VC.NET 'Optimization'


Maybe on some compilers, but it's not guaranteed.  The order of argument
evaluation to functions is not specified by the C++ standard - it's left
up to the implementations.

j

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
Lewin, Gareth
Sent: Tuesday, April 12, 2005 2:02 PM
To: [email protected]
Subject: RE: [GD-Windows] VC.NET 'Optimization'

I fail to see why this worries you, the optimiser is making a (valid)
assumption about your code, and generating the fastest sequence it can.

As a side note, just flip the order of your params to printf, that
should give you want you want. 

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
yogiwp
Sent: Tuesday, April 12, 2005 11:52 AM
To: [email protected]
Subject: Re: [GD-Windows] VC.NET 'Optimization'

> ----------------------------------------------------
>     timer.Restart();
>     printf( "time=%f, result=%d\n", timer.GetElapsed(), fibonacci(42) 
> );
> ----------------------------------------------------


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