Floating point assembler code [modified] - C / C++ / MFC Discussion Boards

Re: The stack conventions are different in AfxBeginThread and CreateThread

Roger Stoltz2-Jul-08 22:23

2-Jul-08 22:23

When you're using MFC you have to use AfxBeginThread due to internal workings of the framework.

For more info:
http://www.flounder.com/badprogram.htm#beginthread[^]

The best starting point for multithreading can be found here[^].

"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown

How to hide a public function inherit from base class

Dracula Wang2-Jul-08 21:27

Dracula Wang

2-Jul-08 21:27

I have 2 classes, B inherit from A, but actually A have a function: fun should not present in B, so I code as blow,

class A{
public:
    virtual void fun(){cout << "a" << endl; };
};

class B : public A{
    virtual void fun(){};
};

But this take no effect, I can call the fun in class b,

int main()
{
    A a;
    B b;
    A *pa = new B;

    a.fun();
    b.A::fun();
    pa->fun();
}

the output is

a
a

How to decline the function call?
Thanks.

Re: How to hide a public function inherit from base class

CPallini2-Jul-08 21:36

CPallini

2-Jul-08 21:36

What is your point?
pa->fun() doesn't fit your needs?

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

[My articles]

Re: How to hide a public function inherit from base class

Dracula Wang2-Jul-08 21:50

Dracula Wang

2-Jul-08 21:50

yes,

the A::fun() is bad for the B, will case error,
so i want let A::fun to be public, but to B the fun must cannot be call

Re: How to hide a public function inherit from base class

CPallini2-Jul-08 21:56

CPallini

2-Jul-08 21:56

What about
(1) Writing A class without fun function.
(2) Writing a (say) AA class that inherits from A and provides fun function.
(3) Writing a B class that inherits from A class and therefore is not able to call fun function?

Of course A class consumers should become AA class ones.

Smile | :)

Re: How to hide a public function inherit from base class

Dracula Wang2-Jul-08 22:05

Dracula Wang

2-Jul-08 22:05

yeah, that's the better way to do,
but in this project others may dislike this implement, they didn't want their code update, @_@.

Thanks for all your help.

Re: How to hide a public function inherit from base class

BadKarma3-Jul-08 1:21

BadKarma

3-Jul-08 1:21

Hi,

I don't understand what you don't want to happen for the B class.

do you want to hide the functionaly from a b object or the declaration;

like this:

int main()
{
 A a;
 B b;

 a.fun();  //  outputs "a"
 b.fun();  //  compiles but doens't do something
 // or
 b.fun();  //  doens't compile

 A* p = &b;
 p->fun(); //  compiles but doens't do something

 b.A::fun();  // compiles but doens't do something
 
}

Maybe you could use the Facade pattern to hide the unwanted A functionaly.

Learn from the mistakes of others, you may not live long enough to make them all yourself.

Floating point assembler code [modified]

Tomerland2-Jul-08 20:56

Tomerland

2-Jul-08 20:56

Dear gurus,

I detected a runtime-bottleneck in my code at the following line

pY[j] = d1 * pY[j] + d2 * pX[j];

.

All variables are floating point. This line is excecuted millions of times.
Now I think about improving runtime by using inline-assembler.

Can somebody give me a hint how to start in the best way (e.g. using a library)

(by the way: I'm not a beginner at assembler-coding)

Kind regards

modified on Thursday, July 3, 2008 5:16 AM

Re: Floating point assembler code

Roger Stoltz3-Jul-08 2:09

Roger Stoltz

3-Jul-08 2:09

Tomerland wrote:
All variables are floating point. This line is excecuted millions of times.
Now I think about improving runtime by using inline-assembler.

I would recommend you to not use inline-asm for various reasons, but the primary reason is "there must be a better way".

A few things to reflect upon:

1. Floating point instructions are slow.
Does it have to be floating points or would integer values suffice?

2. Updating an array of floating points is rarely a "bottleneck" from a data administration point of view. You rarely take time critical actions based upon floating point calculation with e.g. 15-bit exponent and a 64-bit mantissa which is what you have when using long double.
If you're doing this from your GUI thread it will become unresponsive and the user will experience the UI as hung, but that's another problem.
Is it not possible to calculate the new values of the array in a worker thread and post a message to the GUI thread when the calculation has finished?

3. How about using integers that are multiplied by e.g. 100?
When you calculate with the values you have two "decimals", but when you present the value to the user, or store it, you can convert to a floating point value.
I used this technique in an embedded system that had no support for floating point values, but I multiplied with 16 instead which was a good enough approximation.

"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown

Re: Floating point assembler code

Alan Balkany3-Jul-08 4:57

Alan Balkany

3-Jul-08 4:57

A few ideas:

1. Since the line is executed millions of times, you may be able to speed it up with loop unrolling http://en.wikipedia.org/wiki/Loop_unrolling[^].

2. Every time you do pY[j], it requires a multiplication and an addition. If you're processing the array sequentially, it would be faster to start with a pointer to pY[0], then increment it to get the next array element.

If you show some more surrounding code, we may be able to see some other optimizations.

How to struct AA{ struct BB; }; struct BB { struct AA; };

Chesnokov Yuriy2-Jul-08 20:55

Chesnokov Yuriy

2-Jul-08 20:55

How to solve that problem in C language?

//struct BB; ?? Is there something similar as declaring class BB; in C++ ??

struct AA {
struct BB bb;
int a;
};

struct BB {
struct AA aa;
int b;
};

AA has BB member and BB has AA member.

chesnokov

Re: How to struct AA{ struct BB; }; struct BB { struct AA; };

Saurabh.Garg2-Jul-08 21:02

Saurabh.Garg

2-Jul-08 21:02

As far as I know it will not work with C++ either. You have to use pointers to struct's. Like this

struct BB;

struct AA
{
    struct BB* bb;
    int a;
};

struct BB
{
    struct AA aa;
    int b;
};

This will work for C as well.

-Saurabh

Re: How to struct AA{ struct BB; }; struct BB { struct AA; };

Chesnokov Yuriy2-Jul-08 21:33

Chesnokov Yuriy

2-Jul-08 21:33

No that also fails in compilation:

typedef struct _AA {
BB* bb; <--- C2016, C2061
int a;
} AA, *PAA;

typedef struct _BB {
AA* aa; <--- C2016, C2061
int b;
} BB, *PBB;

chesnokov

Re: How to struct AA{ struct BB; }; struct BB { struct AA; };

Saurabh.Garg2-Jul-08 21:40

Saurabh.Garg

2-Jul-08 21:40

You forgot the forward declaration for struct _BB, try this.

struct BB;

typedef struct _AA
{
	struct BB* bb;
	int a;
} AA, *PAA;

typedef struct _BB
{
	struct AA* aa;
	int b;
} BB, *PBB;

-Saurabh

Re: How to struct AA{ struct BB; }; struct BB { struct AA; };

Chesnokov Yuriy2-Jul-08 21:49

Chesnokov Yuriy

2-Jul-08 21:49

But you can not do that???

AA aa;
aa.a = 1;
aa.bb->b = 1; //error???

chesnokov

Re: How to struct AA{ struct BB; }; struct BB { struct AA; };

Saurabh.Garg2-Jul-08 22:10

Saurabh.Garg

2-Jul-08 22:10

Should be aa->bb->b = 1;

-Saurabh

Re: How to struct AA{ struct BB; }; struct BB { struct AA; };

Chesnokov Yuriy2-Jul-08 22:31

Chesnokov Yuriy

2-Jul-08 22:31

???

AA aa; //it is allocated on stack
aa.a = 1; //there is no error here
aa.bb->b = 1; //the error is here stating

error C2037: left of 'b' specifies undefined struct/union 'BB'

You will get the same error with
AA* aa;
aa&gt;bb->b = 1;

chesnokov

Re: How to struct AA{ struct BB; }; struct BB { struct AA; };

Chesnokov Yuriy2-Jul-08 21:42

Chesnokov Yuriy

2-Jul-08 21:42

Oh Yes that one compiled

struct BB;

struct AA {
struct BB* bb;
int a;
};

struct BB {
struct AA* aa;
int b;
};

And that one also.

struct BB;

typedef struct _AA {
struct BB* bb;
int a;
} AA;

typedef struct _BB {
AA* aa;
int b;
} BB;

chesnokov

Re: How to struct AA{ struct BB; }; struct BB { struct AA; };

Stephen Hewitt2-Jul-08 21:10

Stephen Hewitt

2-Jul-08 21:10

See this[^] thread.

Steve

Re: How to struct AA{ struct BB; }; struct BB { struct AA; };

Chesnokov Yuriy2-Jul-08 21:36

Chesnokov Yuriy

2-Jul-08 21:36

I use forwarding references in C++ but I need them in C with structs and it does not work:

struct _BB;

typedef struct _AA {
BB* bb; //error
int a;
} AA, *PAA;

typedef struct _BB {
AA* aa; //error
int b;
} BB, *PBB;

chesnokov

Re: How to struct AA{ struct BB; }; struct BB { struct AA; };

Stephen Hewitt2-Jul-08 21:51

Stephen Hewitt

2-Jul-08 21:51

Try something like this:

"A.h":

// "A.h"
 
#ifndef __A_H__INCLUDED__
#define __A_H__INCLUDED__
 
#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000
 
typedef struct tagB B;
 
typedef struct tagA
{
	B *pB;
} A;
 
#endif // !__A_H__INCLUDED__

"B.h":

// "B.h"
 
#ifndef __B_H__INCLUDED__
#define __B_H__INCLUDED__
 
#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000
 
typedef struct tagA A;
 
typedef struct tagB
{
	A *pA;
} B;
 
#endif // !__B_H__INCLUDED__

Steve

Re: How to struct AA{ struct BB; }; struct BB { struct AA; };

Chesnokov Yuriy2-Jul-08 22:04

Chesnokov Yuriy

2-Jul-08 22:04

I'll see if it will solve the next problem!

That one compiles:
struct BB;
typedef struct _AA {
struct BB* bb;
int a;
} AA, *PAA;

typedef struct _BB {
struct AA* aa;
int b;
} BB, *PBB;

But you can not access BBs contents using AA object??

AA aa;
aa.a = 1;
aa.bb->b = 1; //error???? Ahhhh

chesnokov

Re: How to struct AA{ struct BB; }; struct BB { struct AA; };

Stephen Hewitt2-Jul-08 22:09

Stephen Hewitt

2-Jul-08 22:09

Chesnokov Yuriy wrote:
aa.bb->b = 1; //error???? Ahhhh

Should be as follows:

aa->bb->b = 1;

Steve

Re: How to struct AA{ struct BB; }; struct BB { struct AA; };

CPallini2-Jul-08 22:19

CPallini

2-Jul-08 22:19

You have a lot of patience, man. My 5.
Smile | :)

Re: How to struct AA{ struct BB; }; struct BB { struct AA; };

Chesnokov Yuriy2-Jul-08 22:34

Chesnokov Yuriy

2-Jul-08 22:34

No way

AA aa;
aa->bb??? how can you access with -> object on stack not a pointer??

the glitch is

struct BB;
typedef struct _AA {
struct BB* bb;
int a;
} AA, *PAA;

typedef struct _BB {
struct AA* aa;
int b;
} BB, *PBB;

that one works but you can not access bbs constents from AA nor vice versa?

chesnokov

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