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which one loop is faster and why? Posted by sandeep3047 on 21 Jan 2011 at 10:51 AM

which one is faster

1. for(i=0;i<num;i++)
2. for(i=num;i>0;i--)
assume that no code optimization and microprocessor has flags

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Re: which one loop is faster and why? Posted by AsmGuru62 on 22 Jan 2011 at 6:20 AM

Technically speaking these for loops will NOT do the same work, because index has different values (i will never be EQUAL to num in loop #1, but in loop $2 it WILL). The performance in FOR() part should be the same.

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Re: which one loop is faster and why? Posted by sandeep3047 on 23 Jan 2011 at 12:07 AM

but answer is given that 2nd loop is fast..i don't why there is some condition given regarding flags..

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Re: which one loop is faster and why? Posted by bazzynga on 12 May 2011 at 2:25 PM

As per the dis-assembly in the 1st for loop, an additional instruction is required to set the flag if index has reached the 'num' value. Where as in the 2nd for loop, the index can be directly checked if it's greater than zero.

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