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[vox-tech] totally confused about C promotion
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[vox-tech] totally confused about C promotion



from kernighan and ritchie, page 45:

  For example, the library routine sqrt expects a double argument, and
  will produce nonsense if inadvertantly handed something else.

consider the following code1.c:

   int main(void)
   {
   	long double var = 4.0L;
   
   	printf("%Lf\n", sqrt(var));
   	return 0;
   }

this prints nonsense (0.0000), since sqrt returns double and i'm
printing a long double.  next, consider this code2.c:

   int main(void)
   {
   	long double var = 4.0L;
   
   	printf("%Lf\n", (long double)sqrt(var));
   	return 0;
   }

this works.  but i'm not really interested in just "working" because
this particular code is extremely important to me.  i don't want to base
my code on something that works by accident.

what happens when you hand a long double to a math function which
expects a double?  i can't find any rules for "demotion" in K+R.
does code2.c work by accident or is there a concept of demoting floating
points to a narrower width when the function expects them to be
narrower?

pete

-- 
The mathematics [of physics] has become ever more abstract, rather than more
complicated.  The mind of God appears to be abstract but not complicated.
He also appears to like group theory.  --  Tony Zee's `Fearful Symmetry'

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