if(false) vs if(isNaN) benchmark

[Joseph Rushton Wakeling]

On 07/04/2013 03:05 PM, monarch_dodra wrote:
> Me thinks the test is biased with answering true to isNan. You should first
> initialize your arrays with random [true/false] | [nan/nonan] value. In
> particular, it is more important for isNan to answer "No" as fast as possible,
> rather than actually find nan's. (common, use case is checking that a number is
> *not*) nan. I'd say a mix of 90% rands + 10% Nan's would be representative?

Quite right -- the case of isNaN being false is the case that needs to be really
quick.

> Also, there might be optimizations in bool iteration over double iteration given
> their size, as well as the fact that the "first" test is typically faster.

I'd assumed that putting the start/stop of the stopwatch inside the loop would
address that, but apparently not ...

> I think you should create an array of S{bool; double;} So that the iteration is
> not biased either.
> 
> I'd add a dummy "warmup" loop of 10% of the iterations too, just 'cause.

See attached.  I haven't put in the dummy warmup loop, but as is, there's
consistently less than 2ms difference between the times reported for all
compilers.  If I use rdmd without optimizations, the difference is slightly
larger at 3-5ms.

So, on the basis of that I think I feel happy about using isNaN as a test,
especially as it lets me remove an otherwise superfluous variable from
RandomSample.  Thanks for the advice! :-)
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