Re: asm inline

On Mon, Dec 02, 2002 at 04:12:27PM +0100, Franz Sirl wrote:

quoted

The compiler does the right thing if -fno-strict-aliasing is used or
if 'int b' is replaced by 'ulong b'.

Well, the compiler was right before and as Andreas said, you are wrong. In
C *(ulong*)&B and *&B are different unrelated objects and the compiler
optimizes accordingly.

Indeed. A quick check of the ISO C99 standard revealed that the compiler is
allowed to distinguish between int and long even though they share the
same representation on a particular arch.

Besides the fact that it's almost always right in low-level inline assembly
to use __asm__ __volatile__ (because without the __volatile__ the __asm__
maybe hoisted out of loops if the compiler thinks it's a loop invariant),

...which is desirable in this case. The st_le32 inline is just an efficient
way to flip the endian and is not supposted to have any undeclared
side effects (like touching hardware).

/Samuel


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