AC_DEFUN([AX_C___SYNC_VAL_COMPARE_AND_SWAP], [

  AC_MSG_CHECKING(for __sync_val_compare_and_swap)

  AC_CACHE_VAL(ac_cv___sync_val_compare_and_swap, [

    AC_TRY_LINK(

      [],

      [int a; if (__sync_val_compare_and_swap(&a, 0, 1)) return 1; return 0;],

      ac_cv___sync_val_compare_and_swap=yes,

      ac_cv___sync_val_compare_and_swap=no

    )])

  if test "$ac_cv___sync_val_compare_and_swap" = "yes"; then

    AC_DEFINE(HAVE___SYNC_VAL_COMPARE_AND_SWAP, 1, [define if your compiler has __sync_val_compare_and_swap])

  fi

  AC_MSG_RESULT($ac_cv___sync_val_compare_and_swap)

])