array bound checks

From: [at]} <ftkachov{>
Date: Tue, 18 Feb 2003 12:46:16 +0300 (MSK)

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> The question is whether mandatory range checking unacceptably slow down
> memory access. Does anyone really know?

I've played with this a while ago in program where a (short) array
was used over and over again within a multiple loop.
I tried to replace the array by independent variables
and even by a circular list.
CPU time fluctuated within 1% as a result -- within measurement error.
It was a Pentium/133.

Presumably, the code and data got sucked up
into the innermost cache and the pipelining did its job.

Perhaps, for large arrays the results may be different
but based on my experiences, I do certainly not expect a 20% slowdown
on Intel chips unless the loop contains very few instructions.
If this particular piece of code is embedded into a realistic program,
then one should worry about this only in very exotic situations.

Cheers,
Fyodor Tkachov

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Received on Tue Feb 18 2003 - 10:46:16 UTC