[linux-audio-dev] x86 atomic operations

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Subject: [linux-audio-dev] x86 atomic operations
From: est_AT_hyperreal.org
Date: to syys   30 1999 - 14:51:08 EDT

Paul Barton-Davis discourseth:
>
> yes, they use compare-and-swap, which doesn't exist on the x86 (well,
> it didn't up to the 486 - did Intel come to their senses and add it ?)

Well, here's the 486+ implementation in LinuxThreads:

PT_EI int
__compare_and_swap (long int *p, long int oldval, long int newval)
{
  char ret;
  long int readval;

  __asm__ __volatile__ ("lock; cmpxchgl %3, %1; sete %0"
                        : "=q" (ret), "=m" (*p), "=a" (readval)
                        : "r" (newval), "m" (*p), "a" (oldval)
                        : "memory");
  return ret;
}

I *think* the lock operation makes everything up to the next write
atomic. I'd love it if someone could confirm this. Maybe I just need
to look at an intel manual online.

Eric

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