__CMP_SWAP_LONG

 Performs a conditional atomic compare and exchange operation on a
 longword.  The longword pointed to by source is read and compared
 with the longword old_value.  If they are equal, the longword
 new_value is written into the longword pointed to by source.  The
 read and write is performed atomically, with no intervening access
 to the same memory region.

 The function returns 1 if the write occurs, and 0 otherwise.

 Syntax:

      int __CMP_SWAP_LONG (volatile void *source, int old_value, int
      new_value);