Ambiguous C?

[Piet van Oostrum]

In article <111 at ssp1.idca.tds.philips.nl>, roelof at idca (R. Vuurboom) writes:

 `#define	SCUCMD		0 
 `#define	SCU_BDID	0x2000		/* bit 14 */
 `
 `error()
 `{
 `	if ( (*(int *)(SCUCMD)) & SCU_BDID )
 `		;
 `}

In article <10136 at smoke.BRL.MIL>, gwyn at smoke (Doug Gwyn) writes:

 `state of the bit is.  To force a longword access, it suffices to copy
 `the addressed object into an external longword, because the compiler
 `cannot know what other use might be made of its contents (by other
 `independently-compiled modules) and must therefore pick up the whole

Another simple way is to put the bit to be extracted in a variable, so the
compiler doesn't know to optimize it:

 long	SCU_BDID =	0x2000		/* bit 14 */

This has the advantage that it also works for bit sets.
-- 
Piet van Oostrum, Dept of Computer Science, University of Utrecht
Padualaan 14, P.O. Box 80.089, 3508 TB Utrecht, The Netherlands
Telephone: +31-30-531806. piet at cs.ruu.nl (mcvax!hp4nl!ruuinf!piet)