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/*
* tas() for HPPA.
*
* To generate tas.s using this template:
* 1. cc +O2 -S -c tas.c
* 2. edit tas.s:
* - replace the LDW with LDCWX
* 3. install as src/backend/port/tas/hpux_hppa.s.
*
* For details about the LDCWX instruction, see the "Precision
* Architecture and Instruction Reference Manual" (09740-90014 of June
* 1987), p. 5-38.
*/
int
tas(lock)
int *lock; /* LDCWX is a word instruction */
{
/*
* LDCWX requires that we align the "semaphore" to a 16-byte
* boundary. The actual datum is a single word (4 bytes).
*/
lock = ((uintptr_t) lock + 15) & ~15;
/*
* The LDCWX instruction atomically clears the target word and
* returns the previous value. Hence, if the instruction returns
* 0, someone else has already acquired the lock before we tested
* it (i.e., we have failed).
*
* Notice that this means that we actually clear the word to set
* the lock and set the word to clear the lock. This is the
* opposite behavior from the SPARC LDSTUB instruction. For some
* reason everything that H-P does is rather baroque...
*/
if (*lock) { /* this generates the LDW */
return(0); /* success */
}
return(1); /* failure */
}
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