[RFC] powerpc: optimizing random() and POSIX question

[Raphael M Zinsly <rzinsly at linux dot ibm dot com>]

Hi,

I’m investigating ways to optimize random() for powerpc and got some 
questions regarding POSIX.
The current code on stdlib/random.c does:

long int
__random (void)
{
  int32_t retval;

  __libc_lock_lock (lock);

  (void) __random_r (&unsafe_state, &retval);

  __libc_lock_unlock (lock);

  return retval;
}

If I remove the lock in order to use lqarx/stqcx to access fptr and rptr 
(that are adjacents), then compute the result as is done in random_r, 
will this still be compliant with POSIX?
As the data is accessed atomically, only one thread access the critical 
section at a time. Am I missing something?


Thanks,
--
Raphael Moreira Zinsly
IBM
Linux on Power Toolchain