src/thread.c
@@ -70,5 +70,10 @@ inline s32
 testandset(s32 *addr, s32 val)
 {
-    return __sync_lock_test_and_set(addr, val);
+    int return_value =  *addr;
+    *addr=val;
+    return return_value;
+
+    //It writes value into *ptr, and returns the previous contents of *ptr.
+    //return __sync_lock_test_and_set(addr, val);
 }
 
@@ -76,5 +81,10 @@ inline s32
 testandadd(s32 *addr, s32 val)
 {
-    return __sync_fetch_and_add(addr, val);
+    int return_value =  *addr;
+    *addr+=val;
+    return return_value;
+
+    //These builtins perform the operation suggested by the name, and returns the value that had previously been in memory.
+    //return __sync_fetch_and_add(addr, val);
 }