Re: Loop efficiency

[Rena <hyperhacker@...>]

On 2012-12-19 4:57 PM, "Dirk Laurie" <dirk.laurie@gmail.com> wrote:
>
> There have been a few posts comparing the timing of while,
> ipairs, numeric for with and without the length operator on various
> systems by running loops that do only a couple of additions inside.
>
> Am I the only one who thinks that this sort of test is like
> putting some cars in neutral, have them idle for a couple
> of hours, and measure their fuel consumption?
>
> The moment some real work is done inside the loop, the
> efficiency difference of the loop structure itself (which anyway
> according to the reports seems to be very system-dependent)
> pales into insignificance.
>
> For example, on my system (local 32-bit Ubuntu build from the latest
> source releases) `while` was fastest, at about 0.5 seconds and ipairs
> slowest at about 1.3 seconds.
>
> I replaced the line
>
>     sum = sum + j + v
>
> by
>
>     sum = tostring(v):upper()
>
> and the time jumps to about 15 seconds.  On LuaJIT it jumped
> from 0.3 to to 136 seconds.  I could have got myself a mug of
> coffee.  Bye-bye to the conventional wisdom that LuaJIT is
> faster than PUC-Rio!
>

But the purpose is to measure the loop operation itself, not some busy work inside. Do you mean to say one loop method became this slow and the others didn't? That'd be quite interesting.