Good ways to optimise/optimize code?

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Original post by TheFez
Another thing that can help is assembly. It makes your code longer but it will speed it up (as long as you write your code well).

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Original post by Anonymous Poster
General code optimizing tips: Always use an optimizing compiler. (MSVC Professional, not Standard or Student.)

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Original post by Anonymous Poster
Oops, forgot this... inlining functions won''t save you very much at all (if anything), according to Optimize to the Max - Winning the Passing Game. Use macros instead, it suggests.

A quote: "Looking at the design of modern CPUs it is easy to see that inlining does not provide any performance improvement."

Alistair Keys

.Net defined

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Original post by Anonymous Poster
A quote: "Looking at the design of modern CPUs it is easy to see that inlining does not provide any performance improvement."

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Original post by Anonymous Poster
Stoffel: I must say, I'm more convinced by a columnist for a respected journal than someone saying "it's all rubbish". Explain why you think it's rubbish, and argue with his results. If you don't agree because of some fact, fine. Otherwise, hold your peace.

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Original post by Anonymous Poster
even if a method is inlined, the parameters are still pushed onto the stack or stack-simulating temporary variables. If the method is called or inlined, excessive parameter passing can degrade performance dramatically.

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#include <iostream.h>

#include <time.h>

#include <stdlib.h>


#define maxDef(a, b) (a > b ? a : b)


inline int maxFunc(int a, int b)
{
	return (a > b ? a : b);
}

int main()
{
	srand((unsigned int)time(0));

	int x = rand() % 100;
	int y = rand() % 100;
	
	int max = maxDef(x, y);
	int max2 = maxFunc(x, y);
	
	// Use the variables, or the above code will be optimised out

	cout << max << endl;
	cout << max2 << endl;
	
	return 0;
}
      

; 18   : 	int x = rand() % 100;

	call	_rand
	cdq
	mov	ecx, 100				; 00000064H
	idiv	ecx
	mov	esi, edx

; 19   : 	int y = rand() % 100;

	call	_rand
	cdq
	mov	ecx, 100				; 00000064H
	idiv	ecx

; 20   : 	
; 21   : 	int max = maxDef(x, y);

	mov	eax, esi
	cmp	esi, edx
	jg	SHORT $L1712
	mov	eax, edx
$L1712:

; 22   : 	int max2 = maxFunc(x, y);

	cmp	esi, edx
	jg	SHORT $L1719
	mov	esi, edx
$L1719:
   

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Original post by Anonymous Poster
P.S. I''ll give you a heart attack yet! Wait until I get onto "goto is okay for optimised code" (joking ).

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You might be making the assumption I''m talking about inlining no-parameter functions.

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"As I''ve mentioned in my "Winning the Passing Game" column, even if a method is inlined, the parameters are still pushed onto the stack or stack-simulating temporary variables. If the method is called or inlined, excessive parameter passing can degrade performance dramatically. I witnessed a very good example of this unfortunate truth. My first action was to add the /Oy compiler option for frame pointer omission. Later, I tried an even better solution — I replaced all of the "convenience" methods with macros, thus totally eliminating calling/inlining and the parameter-passing hassle".

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#include <stdlib.h>

inline int multiplyAccumulate (int mac_reg, int tap, int input)
{
    return mac_reg + tap * input;
}

int main ()
{    
    return (int) multiplyAccumulate (3, 5, 2);
}
//dissassembly

PUBLIC	_main
;	COMDAT _main
_TEXT	SEGMENT
_main	PROC NEAR					; COMDAT

; 10   :     return (int) multiplyAccumulate (3, 5, 2);

	push	13					; 0000000dH
	pop	eax

; 11   : }

	ret	0
_main	ENDP
_TEXT	ENDS
END
  

  
#include <stdlib.h>

inline int multiplyAccumulate (int mac_reg, int tap, int input)
{
    return mac_reg + tap * input;
}

int main ()
{    
    return (int) multiplyAccumulate (rand (), rand (), rand ());
}
//disassembly

PUBLIC	_main
EXTRN	_rand:NEAR
;	COMDAT _main
_TEXT	SEGMENT
_main	PROC NEAR					; COMDAT

; 9    : {    

	push	esi
	push	edi

; 10   :     return (int) multiplyAccumulate (rand (), rand (), rand ());

	call	_rand
	mov	edi, eax
	call	_rand
	mov	esi, eax
	call	_rand
	imul	esi, edi
	add	eax, esi
	pop	edi
	pop	esi

; 11   : }

	ret	0
_main	ENDP
_TEXT	ENDS
END
  

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He then goes on to give sample code, which you should investigate. I''m too lazy to do this, but if you do be sure to report the results.

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When I hear your argument, it sounds like religious dogma, of the "I''ve been taught this and I believe it more than you!" school - just like my argument, but from a different perspective.

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Are you willing to change your opinions when presented with new evidence?

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Original post by Stoffel
No part of the C/C++ language is without purpose or utility (except perhaps keyword auto).

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