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IF+IF is quicker than IF+AND or IF+OR
Posted: Sun Apr 26, 2009 8:58 am
by Ollivier
I have the gourdin.
Instead of writing this :
Code: Select all
If Condition1 And Condition2
...
EndIf
It's quicker in the execution writing this:
Code: Select all
If Condition1
If Condition2
...
EndIf
EndIf
... And place in the Condition1 the condition which is considered the most often false.
A second observation is with the OR operation.
Instead of writing this :
Code: Select all
Macro MyMacro()
...
EndMacro
If Condition1 Or Condition2
MyMacro()
EndIf
It's quicker to invert manually the two conditions and write this:
Code: Select all
Macro MyMacro()
...
EndMacro
If (Not Condition1) ; Here, we invert it ('=' becomes '<>', etc...)
If (Not Condition2) ; Here, idem
; Empty line
Else
MyMacro()
EndIf
Else
MyMacro()
EndIf
Ollivier
Posted: Sun Apr 26, 2009 10:54 am
by blueznl
Are you sure? Did you actually benchmark this?
Posted: Sun Apr 26, 2009 10:55 am
by Kaeru Gaman
I suspect it would highly depend on the complexity of the conditions and the size of the codesections to execute...?
how did you test it?
... and why is it a request?
Posted: Sun Apr 26, 2009 1:09 pm
by Michael Vogel
Kaeru Gaman wrote:[...]and why is it a request?
Good question
Maybe Olivier asks for a better code optimization?
Or better control for logical functions (NOT
) ?
Or just some possibilities to keep user defined variables in CPU registers when possible?
Or something completely different?
Michael
Posted: Sun Apr 26, 2009 5:19 pm
by Kaeru Gaman
Posted: Mon Apr 27, 2009 2:35 am
by lexvictory
That's my favourite part of that movie!
Posted: Sat Jun 06, 2009 2:52 pm
by Ollivier
Here is a benchmark:
I obtain a result difference near -33%. (XP 1GHz 1 core)
Code: Select all
;*******************
; And gate test
;*******************
DisableDebugger
; FIRST MODULE
Delay(1)
Begin1 = ElapsedMilliseconds()
For A = 0 To 8000
For B = 0 To 8000
If A And B
EndIf
Next B
Next A
Finish1 = ElapsedMilliseconds()
; SECOND MODULE
Delay(1)
Begin2 = ElapsedMilliseconds()
For A = 0 To 8000
For B = 0 To 8000
If A
If B
EndIf
EndIf
Next B
Next A
Finish2 = ElapsedMilliseconds()
Duration1.F = Finish1 - Begin1
Duration2.F = Finish2 - Begin2
MessageRequester("AND Gate tests", "First module : " + Str(Finish1 - Begin1) + Chr(10) + "Second module : " + Str(Finish2 - Begin2) + Chr(10) + "Duration difference = " + Str(Int(100.0 * Duration2 / Duration1) - 100) + "%")
Posted: Sat Jun 06, 2009 3:04 pm
by AND51
I run this test several times with disabled debugger (don't rely on DisableDebugger alone!) and my results alternate from 0% to -38% (average: 20%).
Testing conditions: PB 4.30 x86 @ Vista x64.
Posted: Sat Jun 06, 2009 3:18 pm
by Kaeru Gaman
Kaeru Gaman wrote:I suspect it would highly depend on the complexity of the conditions and the size of the codesections to execute
with simplest conditions and to code in between, what would be the point in testing it?
anyhow,
it would be nice to know WHY this result occurs,
and it IS nice to know that more-and-simpler lines is faster than less-and-more-complex lines.
Posted: Sat Jun 06, 2009 7:20 pm
by Demivec
Here's some assembly from the speed test code with the respective modules code listed side by side for x86:
Code: Select all
;
; FIRST MODULE ; SECOND MODULE
; ;
; If a And b ; If a
CMP dword [v_a],0 CMP dword [v_a],0
JE No0 JE _EndIf12
; If b
CMP dword [v_b],0 CMP dword [v_b],0
JE No0 JE _EndIf14
Ok0:
MOV eax,1
JMP End0
No0:
XOR eax,eax
End0:
AND eax,eax
JE _EndIf6
; Code inside conditional goes here ; Code inside conditional goes here
; EndIf ; EndIf
_EndIf14:
; EndIf
_EndIf6: _EndIf12:
It seems there's twice as many commands in the First Module's assembled code. My guess is that the simplified method of the Second Module can only be applied to multiple And conditions. When combined with other conditionals (Or and Not) it can get a little more complicated to translate. As a result the more general method of the First Module is used with multiple conditional expressions with the tradeoff of speed.
@Ollivier: if your method could be extended (or specified more completely) somewhat I think it would be adopted by Fred (I hope), barring some other complication.
Posted: Sun Jun 07, 2009 1:55 am
by Rescator
I got 2% to 6% with averaging at 4%.
So the first module was always faster here.
Phenom X3 2.1Ghz.
Posted: Sun Jun 07, 2009 2:07 am
by Rescator
Haha, here's a head scratcher indeed. the previous post was with PureBasic x64.
When I ran the test again with PureBasic x86 I got constantly -27%
The only thing I can think of is that "complex" code runs better on x64 due to twice (!) as many registers being available, or?.
Posted: Sun Jun 07, 2009 12:28 pm
by Ollivier
@Rescator
I deduce it's a problem solved in the version x64. Version I couldn't test actually.
Ollivier
Posted: Mon Jun 08, 2009 8:54 am
by Trond
The test is flawed. The conditions are true once and false 63999999 times, which is not very balanced.
Also, there would realistically be some code within the condition, so let's add some. Suddenly the And version is faster.
I think that the If version is faster with no code within because the processor branch prediction detects that the check is senseless and does some optimizations based on that.
Code: Select all
; FIRST MODULE
Delay(1)
Begin1 = ElapsedMilliseconds()
For A = 0 To 10000
For B = 0 To 10000
If A&1 And B&1
somecode+goes-here
EndIf
Next B
Next A
Finish1 = ElapsedMilliseconds()
; SECOND MODULE
Delay(1)
Begin2 = ElapsedMilliseconds()
For A = 0 To 10000
For B = 0 To 10000
If A&1
If B&1
somecode+goes-here
EndIf
EndIf
Next B
Next A
Finish2 = ElapsedMilliseconds()
Duration1.d = Finish1 - Begin1
Duration2.d = Finish2 - Begin2
MessageRequester("AND Gate tests", "First module : " + Str(Finish1 - Begin1) + Chr(10) + "Second module : " + Str(Finish2 - Begin2) + Chr(10) + "Duration difference = " + Str(Int(100.0 * Duration2 / Duration1) - 100) + "%")
Posted: Mon Jun 08, 2009 12:45 pm
by Demivec
@Trond: With your code I get -23% -> -28% .
I'm running Windows XP Sp3 (x86) on AMD 64 3500+.
With Ollivier's code I had gotten -17% -> -53%.