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C math question

 
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bsturm



Joined: 23 Feb 2009
Posts: 29

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C math question
PostPosted: Tue Mar 03, 2009 3:27 pm     Reply with quote
How does CCS C store intermediate variables that are larger than the final storage type? Like this:

Code:

int16 var1;
int16 var2;

var1=(var2*99)/100;


Clearly the result will fit in var1, but does var1 need to be an int32 to store the intermediate result (var*99)? Or is the intermediate result stored on the stack as an int32? Do I need to cast anything?

Sorry for the newb question, I should know this but I cannot remember.
Sydney



Joined: 13 Feb 2009
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PostPosted: Tue Mar 03, 2009 3:42 pm     Reply with quote
Quote:
does var1 need to be an int32 to store the intermediate result (var*99)?


Yes.

Code:
var1=(int32)var2*99/100
FvM



Joined: 27 Aug 2008
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PostPosted: Tue Mar 03, 2009 4:30 pm     Reply with quote
This behaviour is required by the C standard and not specific to CCS C. An expression gets the type of the "largest" member.
bsturm



Joined: 23 Feb 2009
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PostPosted: Tue Mar 03, 2009 4:33 pm     Reply with quote
Thanks,

I suspected it was that way, but I didn't want to waste a couple of bytes of memory if I didn't have to.
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