Re: trouble using tgmath

Subject: Re: trouble using tgmath
From: Jean-Daniel Dupas <email@hidden>
Date: Thu, 1 Oct 2009 10:42:31 +0200

Le 1 oct. 2009 à 06:06, Nathan Vander Wilt a écrit :

I am trying to use <tgmath.h> to reduce casting while using CGFloat, as recommended: http://www.omnigroup.com/mailman/archive/macosx-dev/2009-June/062331.html

But it's not working as I expect. For example, this code is giving me trouble when compiled for 64-bit:
// CGFloat zoomLevel; (is an ivar)
CGFloat scale = pow(2.0f, -zoomLevel);

Unless I change the function call to pow(2.0f, -(float)zoomLevel), I get "warning: implicit conversion shortens 64-bit value into a 32-bit value" when compiling for 64-bit.

Since the second parameter to pow is a double in the original version, the double version of pow should be used, according to http://www.opengroup.org/onlinepubs/9699919799/basedefs/tgmath.h.html
The macros in <tgmath.h> look like they would make that happen.

I tried something much simpler:
__TGMATH_REAL(1.0, fabs);

But even this gives an implicit conversion warning, on all of gcc 4.0, gcc 4.2, llvm-gcc 4.2!

Why is this happening? Am I totally confused as to how tgmath should be working?

I filled a radar some times ago about this. This warning is about a call in the expanded form of the _expression_.

The expanded macro (which is awful) contains a call to pow(), a call to powf(), a call to powl(), and other variants for complex types. These call are not present in the resulting object as they are stripped done by the compiler, but GCC (spuriously) warns about conversion that would append in these stripped calls.

That said, this issue is fixed in GCC-4.2 on Snow Leopard.

> gcc-4.0 -Wall -Wshorten-64-to-32 -c pow.c

pow.c: In function ‘test’:

pow.c:6: warning: implicit conversion shortens 64-bit value into a 32-bit value

> gcc-4.2 -Wall -Wshorten-64-to-32 -c pow.c

-- nothing

------------- pow.c -------------

#include <tgmath.h>

#include <ApplicationServices/ApplicationServices.h>

int test(double zoomLevel) {

CGFloat scale = pow(2.0f, -zoomLevel);

return (int)scale;

}

-----------------------------------

-- Jean-Daniel

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