is D so slow?
fmohamed at mac.com
Mon Jun 16 07:32:56 PDT 2008
On 2008-06-15 13:53:30 +0200, baleog <maccarka at yahoo.com> said:
> Thank you for your replies! I used malloc instead of new and run time
> was about 1sec
But you probably did not understand why... and it seems that neither
did others around here...
Indeed it is a subtle pitfall in which it is easy to fall.
When you benchmark
1) print something depending on the result like the sum of everything
(it is not the main issue in this case, but doing it would have
probably shown the problem), so you can also have at least a tiny
chance to notice if your algorithm is wrong
operations involving NaNs depending on the IEEE compliance requested on
the processor can be 1000 times slower!!!!!!!!
D (very thoughtfully, as it makes spotting errors easier) initializes
the floating point numbers with NaNs (unlike C).
-> your results follow
if you use malloc, the memory is not initialized with NaNs -> performance
manual malloc in this case is definitely not requested
writing a benchmark can be subtle... benchmarking correct code is easier...
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