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Loop unrolling

Posted on 2002-07-01
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Last Modified: 2010-04-15
What are loop overheads? How are they overcome by unrolling?

Please let me know

Thanks,
Arut
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Question by:arut
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jkr earned 300 total points
ID: 7121621
A 'loop overhead' is e.g.

int i;

for ( i = 0; i < 3; i++) {

 printf ( "i: %d\n", i);
}

Here, checking whether 'i' is smaller than 3 is the overhead.

'Unrolling' would make it

 printf ( "i: %d\n", i);
 printf ( "i: %d\n", ++i);
 printf ( "i: %d\n", ++i);

thus avoiding the overhead. But, you can also see the limitations if the loop bound is not constant.
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