Re: [Bulk] Re: C vs C++

Somehow I thought, that long int is 64 bit. But it is not.
So - who is? long long int, probably?


On Mon, Feb 16, 2015 at 9:38 PM, Mark S Waterbury
<[email protected]> wrote:
> Jevgeni:
>
> I can pretty much guarantee that using 64-bit integers will always win "big
> time" over using packed decimal, even in ILE C/400, from a performance
> standpoint.  All the more so, with ILE C++.
>
> Mark
>
>> On 2/16/2015 2:31 PM, Jevgeni Astanovski wrote:
>>
>> Mark, frankly speaking packed decimal was my suspect since I saw the
>> difference. I saw the difference - it was intuitively clear that the
>> implementations of packed decimal is fundamentally different in C and C++
>> (however unclear why). What I'll do tomorrow, I'll write my own trivial
>> benchmark using decimal arithmetics.
>> Hopefully I shall see the difference.
>> The program uses decimal (15,0), decimal (15,9) and decimal (11,7) - It
>> seems that they all fit into 8 byte int.
>> I'll then see which is better - staying on C and decimals or switch to C++
>> and integers...
>>
>> Thanks,
>> Jevgeni.
>>   On Feb 16, 2015 8:29 PM, "Mark S Waterbury"
>> <[email protected]>
>> 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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