Re: Is there a way to accelerate the following algorithm for hamming distance calculation? By assembly language? - C / C++ / MFC Discussion Boards

Re: Visual Studio C++ compiler empty functions

Daniel Pfeffer25-Mar-15 23:00

25-Mar-15 23:00

It depends on whether the method is virtual. It would theoretically be possible to eliminate all calls to empty non-virtual methods. A virtual method may be overridden by a derived class, so the compiler must perform the virtual call.

(There may be some cases where the compiler can prove that the virtual call refers to the base class. In this case, the compiler could optimize the call away.)

As Richard suggests, the best way to check this is to write a short test program.

If you have an important point to make, don't try to be subtle or clever. Use a pile driver. Hit the point once. Then come back and hit it again. Then hit it a third time - a tremendous whack.

--Winston Churchill

Re: Visual Studio C++ compiler empty functions

Maximilien26-Mar-15 4:38

Maximilien

26-Mar-15 4:38

Yes, the compiler will eliminate useless calls (maybe not in DEBUG mode, but surely in RELEASE mode).

today's compiler are a lot more smarter than you can imagine.

Is there a particular reason for this question?

I'd rather be phishing!

Unable to get WTS_SESSION_LOGON event notification. How to capture the event when user log on to the machine.?

mbatra3124-Mar-15 0:09

mbatra31

24-Mar-15 0:09

Hi,

I have an application which captures Lock, Unlock, Logoff and Logon events of Windows OS. I am able to get the notifications for Lock, Unlock and Logoff, but not getting any notification when user Logs on to the machine. I am using WTS_SESSION_LOGON event to capture the Log on event.

How to capture the event when user log on to the machine.

Any help will be appreciated.

Regards,

Is there a way to accelerate the following algorithm for hamming distance calculation? By assembly language?

prime_tang23-Mar-15 23:37

prime_tang

23-Mar-15 23:37

The following code is a basic algorithm for hamming distance calculation, but due to the design of my application, it requires many times to use this algorithm, in order to improve application efficiency, I want to improve the efficiency of this algorithm, is there any appropriate methods? Assembly language possible?

C++

unsigned dist(const unsigned char *vec1, const unsigned char *vec2, unsigned dim)
{
    const unsigned char popCountTable[] =
    {
        0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4, 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
        1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
        1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
        2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
        1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
        2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
        2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
        3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, 4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8
    };
    unsigned dist_ = 0;
    for (unsigned i = 0; i != dim; ++i)
    {
        dist_ += popCountTable[vec1[i] ^ vec2[i]];
    }
    return dist_;
}

Re: Is there a way to accelerate the following algorithm for hamming distance calculation? By assembly language?

Richard MacCutchan24-Mar-15 3:40

Richard MacCutchan

24-Mar-15 3:40

You should try at http://www.codeproject.com/Forums/326859/Algorithms.aspx[^], but you will need to provide more details of what this algorithm is doing and why your implementation is slow.

Re: Is there a way to accelerate the following algorithm for hamming distance calculation? By assembly language?

Jochen Arndt24-Mar-15 4:14

Jochen Arndt

24-Mar-15 4:14

I don't see much optimisation options.
You are already using a lookup table and the code should not consume much time when dim is small. Rewriting it in assembler will be probably not faster because modern compilers will generate effective code (you may tell your compiler to generate an assembly output to check this).

When the code should be always executed on modern x86 CPUs, you may replace the popcount lookup with the __popcnt x86 instruction. For MS compilers see https://msdn.microsoft.com/library/bb385231.aspx[^].

[EDIT]
When using the popcnt instruction and your data are always a multiple of 2 or 4 (or 8 with 64-bit builds), you can reduce the number of loop executions by performing the operation with 16/32/64 bits.

Re: Is there a way to accelerate the following algorithm for hamming distance calculation? By assembly language?

C^hris L^osinger24-Mar-15 9:06

C^hris L^osinger

24-Mar-15 9:06

Google says: http://bmagic.sourceforge.net/bmsse2opt.html[^]

image processing toolkits | batch image processing

Re: Is there a way to accelerate the following algorithm for hamming distance calculation? By assembly language?

.Shoaib25-Mar-15 6:35

.Shoaib

25-Mar-15 6:35

I wouldn't recommend assembly, unless platform portability is not a concern. A relatively easier option would be to apply a Duff's device to this loop. Unrolling the loop can provide performance boost. However, unless this is, say DSP code that has to run over and over again its probably not worthwhile and the effects wont be noticable.

http://en.wikipedia.org/wiki/Duff%27s_device[^]

I would recommend to benchmark the code first to establish the base data for performance comparison.

Re: Is there a way to accelerate the following algorithm for hamming distance calculation? By assembly language?

jschell25-Mar-15 10:58

jschell

25-Mar-15 10:58

prime_tang wrote:
but due to the design of my application, it requires many times to use this algorithm

First step would of course be to find a design that doesn't require many uses.

That would have a far more significant impact on any speed up of the actual algorithm.

Re: Is there a way to accelerate the following algorithm for hamming distance calculation? By assembly language?

Stefan_Lang8-Apr-15 4:52

Stefan_Lang

8-Apr-15 4:52

I don't see much optimization potential in your function that a decent compiler won't apply already.

That said, the first question you should ask: is there an actual performance bottleneck? Have you measured the time your application takes, and is it really too slow for your purposes?

Second question: if there is a performance issue, which function is causing it? Maybe there are others called alongside this function that take more time and have more optimization potential? Typically, I/O is the slowest part of any application, so reducing I/O to the absolute minimum could already help.

You say it is called often, so the next question would be: can you reduce the number of calls? You said the number of calls is high due to your application design, this implies a different design would require less calls?

GOTOs are a bit like wire coat hangers: they tend to breed in the darkness, such that where there once were few, eventually there are many, and the program's architecture collapses beneath them. (Fran Poretto)

Link Error Which .lib to include

ForNow21-Mar-15 19:28

ForNow

21-Mar-15 19:28

Hi
I have a Console C project that has a number of DLL's

I got the following error when linking

Quote:
error LNK2001: unresolved external symbol _DllMainCRTStartup@12

I am linking it as 64 bit

How would I know what .lib to include by googling seemed it was MSVCRT.LIB
but that didn't resolve my problem

I remember once using dependency walker to resolve symbols but I think that was looking at .DLL to see what entry points were exposed

Thanks

Re: Link Error Which .lib to include

Richard MacCutchan21-Mar-15 23:58

Richard MacCutchan

21-Mar-15 23:58

Check the documentation for the DLL methods that you are calling. For example Google can find you https://www.google.com/search?q=DllMainCRTStartup[^].

Re: Link Error Which .lib to include

ForNow22-Mar-15 16:50

ForNow

22-Mar-15 16:50

Thank you again Richard the problem was in my win32.mak

I have amd64 cpu and for some reason win32 it was i386 thus generating @12 ordinal for

The DLL startup entry point

still trying to finish building

Re: Link Error Which .lib to include

Frankie-C23-Mar-15 0:36

Frankie-C

23-Mar-15 0:36

So I was right 64bits objs and 32bits linking... Smile | :)

Re: Link Error Which .lib to include

ForNow23-Mar-15 2:10

ForNow

23-Mar-15 2:10

Yes thanks

Re: Link Error Which .lib to include

Frankie-C22-Mar-15 0:19

Frankie-C

22-Mar-15 0:19

If you are linking for 64bits the entry point for dll should be _DllMainCRTStartup (undecorated entry point). If you get this error probably there is a error in linker switches because it seems that you are trying to use 64 bits objects in a 32bits link.
It is not very clear in which part of your project you're getting the error: compiling the console exe or one of the DLL?

modified 22-Mar-15 6:58am.

MALLOC FUNCTION IMPLEMENTATION

Member 1154244420-Mar-15 10:45

Member 11542444

20-Mar-15 10:45

SIR,
I want to define my own malloc function in c++ using new operator..

Re: MALLOC FUNCTION IMPLEMENTATION

PIEBALDconsult20-Mar-15 11:35

PIEBALDconsult

20-Mar-15 11:35

Thanks for the warning. Good luck.

Re: MALLOC FUNCTION IMPLEMENTATION

jeron120-Mar-15 11:56

jeron1

20-Mar-15 11:56

and the question is?

"the debugger doesn't tell me anything because this code compiles just fine" - random QA comment

"Facebook is where you tell lies to your friends. Twitter is where you tell the truth to strangers." - chriselst

Re: MALLOC FUNCTION IMPLEMENTATION

jschell20-Mar-15 13:03

jschell

20-Mar-15 13:03

A very simple and realistically non-worthwhile implementation is simple. Your malloc calls new with an byte array. Then your free, which you would also implement would use delete to delete the array.

If you want a learning experience however then you should do the following in the specified order.
1. Learn what stack and list are and how to implement them.
2. Specifically learn how to implement them using sequential memory and not just pointers.
3. Learn how malloc is generally implemented. You will need substantial understanding of 1/2 to understand this.
4. Implement your own heap management. (Which you will understand after doing 1/2/3.)

How to use MFC to design an app that can connect 2 types of database

DHLao19-Mar-15 17:36

DHLao

19-Mar-15 17:36

I never use VC++ to develop an app that use to connect and update database before.

My app is design to allow user to update the database by supply MS Excel file.

When the app open, user need to choose either connect to MS Access 2010 (.mdb) or MSSQL 2014 express.

By using MFC Application Wizard, I need to choose which client type to use at Database support section (ODBC or OLEDB).

After reference to the doc on the web. Seems that OLEDB suitable for Access and ODBC suitable for MSSQL.

This make me has a difficulty to choose between them during start.

Or I should create a project that has no database support at start, then add DLL that support database to this solution later.

But the wizard that use to create MFC DLL and ATL Project has no section for choose database support.

Any advice and suggestion that direct me how to start is appreciated.

Re: How to use MFC to design an app that can connect 2 types of database

Jochen Arndt19-Mar-15 22:38

Jochen Arndt

19-Mar-15 22:38

There are no limitations to support different types of databases in one application. The application wizard only prepares the project to support a specific database interface. Support for other interfaces can be added later manually.

My suggestion:
Create two new empty projects with support for different database interfaces. Then choose one as your project and add the necessary definitions from the created source files of the other project by comparing the files.

Re: How to use MFC to design an app that can connect 2 types of database

DHLao19-Mar-15 23:06

DHLao

19-Mar-15 23:06

Thanks for reply.
Since wizard can relief my work. I just think is it possible to select both ODBC and OLEDB by using wizard.
If it is not possible, I have to implement the code myself.
That's hell a lot of work Dead | X|

Re: How to use MFC to design an app that can connect 2 types of database

Jochen Arndt19-Mar-15 23:29

Jochen Arndt

19-Mar-15 23:29

The selection uses radio buttons. So only one can be selected.

You must write the code to access the database anyway. The wizard will not do that. It just prepares your project. Merging two empty projects into one is not much work.

Re: How to use MFC to design an app that can connect 2 types of database

jschell20-Mar-15 13:06

jschell

20-Mar-15 13:06

Note that reading even a trivial excel file in an application can be a difficult task.
Once you have read the data the user interface and writing to a database is easier because there are more sources that one can learn from.

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.