Re: Execution time of code?
* coal@mailvault.com:
On Mar 6, 10:00 pm, "Alf P. Steinbach" <al...@start.no> wrote:
* c...@mailvault.com:
The thing about clock is
it returns values like 10,000, 20,000, 30,000, 50,000, 60,000, etc.
I would be more comfortable with it if I could get it to round
its results less.
For a difference between 'clock' results, i.e. a time interval expressed in
'clock' units, convert to 'double' and then divide by CLOCKS_PER_SEC.
But note: do that /after/ any subtraction of end time from start time.
I'm aware of that, but don't see the point here. Both the Boost and
Ebenezer numbers would be divided by the same constant. It is
simpler,
I think, to just add up the times from clock for each version and then
figure out the ratio.
How is that different from what you quoted?
I was commenting on the "problem" with values like "10,000".
If you *really*, actually, have values like those you exemplified, like
"10,000", then that indicates with high probability that somewhere in the
testing code an integer division is used where a floating point division should
have been used.
But I assumed that was not the case, that it was just a case of dramatizing the
effect of low resolution.
If you really, actually have such values, then check out the division of 'clock'
result.
(I could document the results from clock, but
for now I just document the ratio.) I use semicolons within a shell
to run each version 3 times in a row. I execute that command twice.
The second group starts up right on the heels of the first. So the
test is run 6 times total. I ignore the first 3 runs/times and do
those just to get the machine ready for the next 3. Anyway, my
impression, and it seemed like Victor has a similar impression, is
the output from clock isn't as precise as it could be. The range
I got earlier from clock, 1.4 - 4.5, leaves quite a bit of room for
manipulation if that is a person's goal.
Uh, the person doing the timing is presumably /not/ your adversary, but yourself?
Anyways, if you have a range of 1.4 to 4.5 for the same code, tested in *nix
(indicated by your comment about semicolons), using 'clock' which in *nix-land
reports processor time, then Something Is Wrong.
Perhaps the integer division issue mentioned above?
Cheers & hth.,
- Alf
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