Re: C vs C++

[Mark S Waterbury <mark.s.waterbury@xxxxxxxxxxxxx>]

Jevgeni:

Yes, the overhead of converting the data to and from packed decimal 
needs to be considered, when working with the data in other formats.

Support for financial data is why IBM developed "packed decimal" support 
in the first place, on the IBM mainframes (S/360, S/370, S/390, 
z/Series). It looks like the IBM z/OS XL C compiler also supports packed 
decimal directly, in the same way that ILE C/400 does, and the IBM C++ 
compiler on the mainframe uses the same "BCD" library, the same way ILE 
C++ does.

IBM has made some improvements in each new generation -- Power4, Power5, 
Power6, Power7 and Power8, with regard to better support for "packed 
decimal" arithmetic and what is called "decimal floating point,"  so I 
am not surprised that your results are different from mine.  (That is 
why I posted the source code, so that anyone can try it on their systems.)

I think this is the right approach -- to test various coding 
alternatives, and measure the results, before deciding which way to go, 
for your "live" production applications.

All the best,

Mark S. Waterbury

> On 2/17/2015 8:56 AM, Jevgeni Astanovski wrote:
> Mark,
>
> Spent some time and rewrote the API to use long long.
> However I have nothing to do about the data that I'm processing.
> I work in the finance area so effectively my API works not with
> numbers - rather with money.
> And all the money in the tables is kept as packed decimals.
> So what I did - I read packed decimals and immediately convert them to
> long long before I make some arithmetics with them.
> Result is still the same - 2 times slower than the C version...
>
> I'll now go and experiment with the benchmarking program of yours to
> see what consumes time. If conversion of packed to int (or long) is
> most ti,e consuming, then probably I'm digging in the wrong
> direction.....