atomic.h

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/* PROLOG END TAG zYx                                              */
/*
 * atomic.h - PPE atomic SHM counter operations.
 *
 * Interfaces patterned after, and hopefully compatible
 * with PowerPC64-Linux atomic counter operations.  Uses
 * 32b values for various counters.
 */
#ifndef _PPU_ATOMIC_H_
#define _PPU_ATOMIC_H_

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

typedef unsigned int atomic_t __attribute__ ((aligned (128))); 


/* atomic_ea_t is a 64bit effective address  that points to 
 * an atomic_t variable 
 */
typedef unsigned long long atomic_ea_t;

/**
 * ASSUMPTIONS:
 * On the PPE, the size of a reservation granule is 128 bytes
 * (a cache-line), so when a programmer puts a reservation on an
 * address, that whole cacheline is reserved. Therefore both
 * the PPE and SPE can participate in an atomic operation as long as
 * lwarx and getllar operate on the same cacheline. 
 */ 


/*
 * atomically loads and replaces the value v with val. 
 * Returns the old value at v
 */ 
static __inline int _atomic_replace(atomic_ea_t v, int val)
{
  int old;
  void *p;

  SYNC_ULL_TO_PTR(v, p);

  do {
    old = (int)__lwarx(p);
  } while (__stwcx(p, (unsigned int)val) == 0);

  return old;
}


/*
 * atomically loads the value at v, adds val, replaces the
 * value at v with the sum. Returns the old value at v
 */ 
static __inline int _atomic_modify(atomic_ea_t v, int val)
{
  int oldval, newval;
  void *p;

  SYNC_ULL_TO_PTR(v, p);

  do {
    oldval = (int)__lwarx(p);
    newval = oldval + val;
  } while (__stwcx(p, (unsigned int)newval) == 0);

  return oldval;
}


#endif /* _PPU_ATOMIC_H_ */