Re: C vs C++

Mark,

Not used to just believe, I repeated your test.
I also tried to substitute 11,0 that you use with 15,0 that I use - to
see its effect.
Probably my box is slightly more powerful :-) but the trend is exactly the same:
C and decimal(11,0) : 470ms
C++ and decimal(11,0) : 23900ms
C and decimal(15,0) : 560ms
C++ and decimal(15,0) : 25500ms
Turning optimization on reduces the time to 21000 ms - but it is still
so far from what is seen in C.

I'll go and see what can be done with the sources to decrease the use
of packed....
:-((((

Jevgeni.




On Mon, Feb 16, 2015 at 9:32 PM, Mark S Waterbury
<[email protected]> wrote:
> Jevgeni:
>
> To confirm my hypothesis, I made a few small changes to that BENCH.C
> program, now re-posted as BENCHBCD.C here:
>
>     http://code.midrange.com/136eb55598.html
>
> When I run this here, the differences in elapsed time is much worse than
> just twice as slow -- the C++ version took 24 times longer than the C
> version -- 8 seconds versus 3 minutes and 16 seconds -- Tis example, dping
> all of those loops, and dong lots of BCD math, grossly exaggerates the
> differences between the overhead of procedure/function calls to library
> routines in ILE C++, versus "in-line" code in ILE C..
>
> Mark
>
>> On 2/16/2015 1:29 PM, Mark S Waterbury wrote:
>>
>> Jevjeni:
>>
>> I just noticed near the bottom of your post, where you said:
>>
>>     Program makes a lot of calculations with packed decimal.
>>
>> There is a big difference in the way ILE C implements support for "packed
>> decimal" as a "native" data type -- versus the way it is "supported" in ILE
>> C++ -- in ILE C, the compiler directly genrerates in-line code (in WCode /
>> NMI)  to work on packed decimal data.  In the ILE C++ compiler, support for
>> "packed decimal" is through a C++ library called "BCD" -- there are a lot of
>> macros and such defined in the QSYSINC/H include member named BCD ... if you
>> take a peek at that member, I think you will see that this uses "operator
>> overloading" in C++ to trick the compiler into calling the desired library
>> functions when operations are performed on "packed decimal" data.
>>
>> This difference could easily account for the big differences you are
>> seeing.
>>
>> And then, you said:
>>
>>     ... is there anything that can be done about it?
>>
>> In C++, you could look into converting the packed decimal data into 64-bit
>> integers, and then performing any calculations using those long integers.
>> This would be much faster than using packed decimal arithmetic, then convert
>> back to packed decimal format, if needed.  Or, just stick with ILE C/400 for
>> those programs that require doing a lot of packed decimal arithmetic
>> operations.
>>
>> Hope that helps,
>>
>> Mark S. Waterbury
>>
>
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