Re: [KJ] Correct imprecise >= comparisons

[Eric Sesterhenn <snakebyte@gmx.de>]

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hi,

> in the kernel source tree, there are several places (less important ones
> and high-profile ones such as TCP/IP) which do "incorrect" checks such as:
> 
> if (val >= max)
>   val = max;
> 
> which can instead be expressed as
> 
> if (val > max)
>   val = max;
>
> in order to cut down on both executed cycles and cache write invalidation.

I am wondering if it is actually worth the effort, since it seems to
me as if this would normally be an exception that val >= max. And
instead of returning with an error or aborting you normalize the value.
Therefore the val=max statement is just executed pretty rarely, when an
user supplies a bad value for example. Even if there would be something
like

foo(int x){
	if (x>=2000)
		x=2000;
	// more code
}

bar (void){
	for (int i=0; i<4000; i++)
		foo(i);
}

you just win in one of the many cases...

Just my 2 Cents :)
Eric


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