On Thursday, 4 July 2013 at 12:53:48 UTC, Joseph Rushton Wakeling
wrote:
Hi all,
A trivial little benchmark for comparing the performance of a
function using
if(!booleanValue) as a conditional, versus one using
if(isNan(x)).
Run with dmd -O -release -inline -noboundscheck on my system, I
find the two are
virtually equivalent, with it taking about 30ms for 1 million
if(!boolean)
versus about 31 for a million if(isNaN(floatingpoint)).
With ldmd2 and the same optimizations, I get about 25 compared
to 27-28 ms for
the two cases, again with a million realizations of each.
Finally, with gdmd I get 30ms for a million if(!boolean) versus
about 150ms for
a million if(isNaN(floatingpoint)).
Code attached, feel free to critique. Generally I think these
results show that
the difference between checking a boolean and checking isNan
are negligible, but
I'm surprised at the relatively bad performance with gdmd and I
wonder if
there's some particular reason for this.
The relevance is to a fix I'm preparing for this bug:
http://d.puremagic.com/issues/show_bug.cgi?id=10322
See also:
http://forum.dlang.org/post/lcrwybqszclitzrav...@forum.dlang.org
Thanks in advance for any feedback :-)
Best wishes,
-- Joe
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?
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 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.
Gotta go.
