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| Author |
Message |
calvin
Joined: 18 Aug 2010
Posts: 10
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| Int32 comparison problem |
 Posted: Fri May 06, 2011 12:43 am |
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Hi!
I have a the following code:
| Code: |
int32 AA,BB;
AA=-4;
if(AA > 0){
// do some thing 1
}
BB=0:
if(AA > BB){
// do some thing 2
}
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Allways the code executes "do some thing 1" and "do some thing 2".
Why??
Thanks for your help |
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calvin
Joined: 18 Aug 2010
Posts: 10
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| Another case: |
| Posted: Fri May 06, 2011 1:01 am |
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For more illustration:
| Code: |
if(-2 < -4){
EVENTO(196);
}
if(-2 > -4){
EVENTO(197);
}
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CCS generates the following .lst
| Code: |
.................... if(-2 < -4){
.................... EVENTO(196);
.................... }
....................
.................... if(-2 > -4){
.................... EVENTO(197);
2156: MOVLW C5
2158: MOVWF x9C
215A: MOVLB 0
215C: CALL 0CE6
.................... }
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why??? |
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FvM
Joined: 27 Aug 2008
Posts: 2337
Location: Germany
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| Posted: Fri May 06, 2011 1:47 am |
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With 8 Bit CCS compilers, int defaults to unsigned (unless overridden by a #TYPE statement).
So all negative constants are interpreted as positive values, the result is correct. |
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calvin
Joined: 18 Aug 2010
Posts: 10
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| Posted: Fri May 06, 2011 7:02 am |
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| Thanks FvM I will read about that.But, is fine too that the compile doesnt generate code for some statements? that is not for signed or unsigned data types. |
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SherpaDoug
Joined: 07 Sep 2003
Posts: 1640
Location: Cape Cod Mass USA
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| Posted: Fri May 06, 2011 8:27 am |
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If the compiler can tell at compile time that certain code can never be reached, it will not generate machine code for those statements. They are optimized out of existence.
_________________
The search for better is endless. Instead simply find very good and get the job done. |
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FvM
Joined: 27 Aug 2008
Posts: 2337
Location: Germany
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| Posted: Fri May 06, 2011 8:36 am |
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| Quote: | | But, is fine too that the compile doesnt generate code for some statements? |
Sure. Conditional code after a constant compare that evaluates to false will be removed. |
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calvin
Joined: 18 Aug 2010
Posts: 10
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| Posted: Fri May 06, 2011 11:54 am |
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| Thanks to all for your help. |
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