Add header for simple atomic operations

include/ucore/atomic.h

@@ -0,0 +1,44 @@
+#ifndef UC_ATOMIC_H_
+#define UC_ATOMIC_H_
+
+#ifdef __GNUC__
+
+
+/**
+ * Atomically add val to *ptr
+ * @return *ptr before the addition
+ */
+#define UC_ATOMIC_ADD(ptr, val) __sync_fetch_and_add((ptr), (val))
+
+/**
+ * Atomically subtract val to *ptr
+ * @return *ptr before the subtraction
+ */
+#define UC_ATOMIC_SUB(ptr, val) __sync_fetch_and_add((ptr), -(val))
+
+/**
+ * Atomically decrement *ptr
+ * @return *ptr before the decrement
+ */
+#define UC_ATOMIC_DEC(ptr) UC_ATOMIC_ADD((ptr), -1)
+
+/**
+ * Atomically increment *ptr
+ * @return *ptr before the increment
+ */
+#define UC_ATOMIC_INC(ptr) UC_ATOMIC_SUB((ptr), 1)
+
+
+/**
+ * UC_ATOMIC_CAS(p, 12, 
+ * Compare-And-Swap. If *ptr is oldval, write newwal to *ptr. 
+ * @return *ptr that was before the operation.
+ */
+#define UC_ATOMIC_CAS(ptr, oldval, newval) __sync_val_compare_and_swap((ptr), (oldval), (newval))
+
+#else
+#error "No atomic operations implemented for this compiler"
+#endif
+
+
+#endif