Re: C vs C++

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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