atomic_dec_if_positive.h

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/* PROLOG END TAG zYx                                              */
#ifndef _PPU_ATOMIC_DEC_IF_POSITIVE_H_
#define _PPU_ATOMIC_DEC_IF_POSITIVE_H_

#include <ppu_intrinsics.h>
#include "sync_utils.h"
#include "atomic.h"

/*
 * atomic_dec_if_positive - atomically decrement if counter is positive.
 *
 *  v: handle to effective address of counter.
 * 
 * Atomically decrement a counter if its value is positive.
 * The only restriction is that v must be word aligned.
 *
 *
 * Returns the old value of the counter, minus 1.
 */
static __inline int _atomic_dec_if_positive(atomic_ea_t v)
{
  int ret;
  int tmp;
  void *p;

  SYNC_ULL_TO_PTR(v, p);

  do {
    tmp = (int)__lwarx(p);
    ret = tmp - 1;
    tmp = (tmp > 0) ? ret : tmp; 
  } while (__stwcx(p, (unsigned)tmp) == 0);

  return ret;
}

#endif /* _PPU_ATOMIC_DEC_IF_POSITIVE_H_ */