Re: Speeding up a loop - C / C++ / MFC Discussion Boards

Re: How to handle notify message in both reflect way and normal way?

followait3-Mar-08 21:26

followait

3-Mar-08 21:26

It doesn't work. When I send WM_NOTIFY in the ctrl's notify message handler, it seems that there is a deadlock.

[solved]

followait3-Mar-08 22:16

followait

3-Mar-08 22:16

Just another way, send my msg instead. Laugh | :laugh:

Speeding up a loop [modified]

⁷³Zeppelin3-Mar-08 20:51

⁷³Zeppelin

3-Mar-08 20:51

I've been doing some profiling and have come across a portion of my code that I suspect can be sped up (although it is already quite simple). I have a loop where I do a calculation. In this form:

for (int i = max; i >= 0; i--)
    for (int j = 0; j <= limit; j++)
        value = calculation(i,j);

The loop is blazingly fast. I can do about 20,000 iterations in a fraction of a second. Then I added an if-elseblock:

for (int i = max; i >= 0; i--) {
    for (int j = 0; j <= limit; j++) {
        if (quantity > 0)
            value = calculation(i,j);      // calculation dependent on i and j
        else
            value = 0.0;
    }
}

In the above form, the 20,000 iterations can take about a minute. Speed is very important and the simple addition of the if-else brings a huge performance hit - I suspect because the compiler can't optimize the loop. Does anyone see a creative way to remove this if-else block and replace it with something the compiler can optimize? It seems it should be simple, but I can't really think of anything off-hand.

modified on Tuesday, March 4, 2008 3:29 AM

Re: Speeding up a loop

Maxwell Chen3-Mar-08 20:58

Maxwell Chen

3-Mar-08 20:58

73Zeppelin wrote:
for (int i = max; i >= 0; i--) { for (int j = 0; j <= limit; j++) { if (quantity > 0) value = calculation(); else value = 0.0; }}

if(quantity > 0) {
  // the loop
  // plus: value = calculation();
}
else {
  // the loop
  // plus: value = 0;
}

Maxwell Chen

Re: Speeding up a loop

⁷³Zeppelin3-Mar-08 21:28

⁷³Zeppelin

3-Mar-08 21:28

Hi Maxwell, thanks. I should have mentioned the calculation is indexed by the loop. I've been thinking of something like:

#define MAX(x,y) ((x)>(y)) ? (x) : (y)

but then I have to calculate x on each iteration so that isn't an improvement.

Re: Speeding up a loop

CPallini3-Mar-08 22:00

CPallini

3-Mar-08 22:00

if quantity is not i, j dependent then Maxwell suggestion still applies.
Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

Re: Speeding up a loop

⁷³Zeppelin3-Mar-08 22:16

⁷³Zeppelin

3-Mar-08 22:16

Yes, of course! We shouldn't mislead anyone. Good of you to point that out.

Re: Speeding up a loop

El Corazon4-Mar-08 8:37

El Corazon

4-Mar-08 8:37

well... assuming that is not a poor example... if quantity is not based on i,j why is it inside a loop? Since value is assigned not summed or similar, only the last value of the loop is stored. You could count backwards and stoop on the first hit and get the same result.

_________________________
Asu no koto o ieba, tenjo de nezumi ga warau.
Talk about things of tomorrow and the mice in the ceiling laugh. (Japanese Proverb)

Activex + Network Credentials

Aamol M3-Mar-08 20:43

Aamol M

3-Mar-08 20:43

I am using activex in VC application. It has some connect method which takes User Name and passwords.
When I give user name and password of remote machine or network machine. Connect fucntion gives error : "Invalid Network Credentials".

Does anyone came across this or know what I have to set to by pass this network credentials problem.

Thanks in advance Smile | :)

AmolM

Reading from file and displaying in screen

Chandrasekharan P3-Mar-08 18:51

Chandrasekharan P

3-Mar-08 18:51

I want to display a value from the file and display it on the editbox. for example
in the file the time format is something like this

11:06:16:254

now i need to put 11 in one editbox, 06 in the next editbox and so on... that means i will have 4 edit boxes to display the time.

the file format that i have is of .dat extension. i am using mfc for this

please give me some leads.

Re: Reading from file and displaying in screen

Rajesh R Subramanian3-Mar-08 19:08

Rajesh R Subramanian

3-Mar-08 19:08

You have a problem reading from the file or displaying it on the screen?

Nobody can give you wiser advice than yourself. - Cicero
.·´¯`·->Rajesh<-·´¯`·.
Codeproject.com: Visual C++ MVP

Re: Reading from file and displaying in screen

Chandrasekharan P4-Mar-08 17:25

Chandrasekharan P

4-Mar-08 17:25

i am able to read the data from a file but i am can display only the last value of the file. i want to display all the values in that file. i have created a timer for that which fires every one sec. what needs to be done to show all the values in the editbox.

Re: Reading from file and displaying in screen

led mike3-Mar-08 19:10

led mike

3-Mar-08 19:10

Chandrasekharanp wrote:
please give me some leads.

1) research the MFC library documentation for File I/O. This will provide you with the ability to open the file and read data from it.

2) research the MFC documentation for the class CString. This will provide you with solutions for separating the different parts of the time data.

3) Research the MFC CEdit control. This will lead you solutions for displaying the edit controls and setting the data into them.

4) Thank your instructor for giving you such a simple assignment.

led mike

Re: Reading from file and displaying in screen

Mark Salsbery4-Mar-08 5:55

Mark Salsbery

4-Mar-08 5:55

Priceless[^] Smile | :)

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Re: Reading from file and displaying in screen

led mike4-Mar-08 8:50

led mike

4-Mar-08 8:50

hehehe

So far today I'm liking this one[^]

led mike

Re: Reading from file and displaying in screen

Mark Salsbery4-Mar-08 8:57

Mark Salsbery

4-Mar-08 8:57

Wow

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Re: Reading from file and displaying in screen

led mike4-Mar-08 9:03

led mike

4-Mar-08 9:03

Yeah hahaha, he's got a tight grip on that whole critical thinking thing eh? Laugh | :laugh:

led mike

Re: Reading from file and displaying in screen

Mark Salsbery4-Mar-08 9:10

Mark Salsbery

4-Mar-08 9:10

Logic? We don't need no steenking logic!

Laugh | :laugh:

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Re: Reading from file and displaying in screen

Mark Salsbery4-Mar-08 9:12

Mark Salsbery

4-Mar-08 9:12

~~Hey what happened to CPhog?~~

Never mind - I restarted FF and all is well Smile | :)

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Re: Reading from file and displaying in screen [modified]

led mike4-Mar-08 9:15

led mike

4-Mar-08 9:15

Mark Salsbery wrote:
Hey what happened to CPhog?

I'm using it to post this?

Damn! Missed the opportunity to say "It works on my machine!" Poke tongue | ;-P

Last modified: 12mins after originally posted --

led mike

Re: Reading from file and displaying in screen

Mark Salsbery4-Mar-08 9:16

Mark Salsbery

4-Mar-08 9:16

hehe see my modified post Smile | :)

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Re: Reading from file and displaying in screen

Hamid_RT3-Mar-08 20:44

Hamid_RT

3-Mar-08 20:44

You need to CFile class and CString then you can use of SetWindowText for show values on the editbox.

Re: Reading from file and displaying in screen

Rajesh R Subramanian3-Mar-08 20:48

Rajesh R Subramanian

3-Mar-08 20:48

Hamid. wrote:
you can use of SetWindowText for show values on the editbox

Don't you like the idea of having a member variable? Do you really need SetWindowText to set text of an edit box in MFC? WTF | :WTF:

Nobody can give you wiser advice than yourself. - Cicero
.·´¯`·->Rajesh<-·´¯`·.
Codeproject.com: Visual C++ MVP

Re: Reading from file and displaying in screen

Hamid_RT3-Mar-08 20:59

Hamid_RT

3-Mar-08 20:59

Yeah I agree with you.

Re: Reading from file and displaying in screen

David Crow4-Mar-08 2:44

David Crow

4-Mar-08 2:44

Rajesh R Subramanian wrote:
Don't you like the idea of having a member variable?

Sure, as long as it's a CEdit variable.

Rajesh R Subramanian wrote:
Do you really need SetWindowText to set text of an edit box in MFC?

No, but the other alternative can, and often does, cause problems that are easily avoidable.

"Normal is getting dressed in clothes that you buy for work and driving through traffic in a car that you are still paying for, in order to get to the job you need to pay for the clothes and the car and the house you leave vacant all day so you can afford to live in it." - Ellen Goodman

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

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