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
<mark.s.waterbury@xxxxxxxxxxxxx> 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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