acx_restrict

This macro determines whether the C compiler supports the "restrict" keyword introduced in ANSI C99, or an equivalent. Does nothing if the compiler accepts the keyword. Otherwise, if the compiler supports an equivalent (like gcc's __restrict__) defines "restrict" to be that. Otherwise, defines "restrict" to be empty.

AC_DEFUN([ACX_C_RESTRICT],
[AC_CACHE_CHECK([for C restrict keyword], acx_cv_c_restrict,
[acx_cv_c_restrict=unsupported
 AC_LANG_SAVE
 AC_LANG_C
 # Try the official restrict keyword, then gcc's __restrict__, then
 # SGI's __restrict.  __restrict has slightly different semantics than
 # restrict (it's a bit stronger, in that __restrict pointers can't
 # overlap even with non __restrict pointers), but I think it should be
 # okay under the circumstances where restrict is normally used.
 for acx_kw in restrict __restrict__ __restrict; do
   AC_TRY_COMPILE([], [float * $acx_kw x;], [acx_cv_c_restrict=$acx_kw; break])
 done
 AC_LANG_RESTORE
])
 if test "$acx_cv_c_restrict" != "restrict"; then
   acx_kw="$acx_cv_c_restrict"
   if test "$acx_kw" = unsupported; then acx_kw=""; fi
   AC_DEFINE_UNQUOTED(restrict, $acx_kw, [Define to equivalent of C99 restrict keyword, or to nothing if this is not supported.  Do not define if restrict is supported directly.])
 fi
])