tuklib_integer.m4: Optimize the check order.

The __builtin byteswapping is the preferred one so check for it first.

diff --git a/m4/tuklib_integer.m4 b/m4/tuklib_integer.m4
index dcc83d92ba162987fe6bbfdbb9887f7d2fe27e75..e9741ef64d7248d82d20bfa52ccb0bd7d09b42ff 100644 (file)
--- a/m4/tuklib_integer.m4
+++ b/m4/tuklib_integer.m4
@@ -7,7 +7,7 @@
 #
 #   Checks for tuklib_integer.h:
 #     - Endianness
-#     - Does operating system provide byte swapping macros
+#     - Does the compiler or the operating system provide byte swapping macros
 #     - Does the hardware support fast unaligned access to 16-bit
 #       and 32-bit integers
 #
@@ -22,13 +22,28 @@
 AC_DEFUN_ONCE([TUKLIB_INTEGER], [
 AC_REQUIRE([TUKLIB_COMMON])
 AC_REQUIRE([AC_C_BIGENDIAN])
-AC_CHECK_HEADERS([byteswap.h sys/endian.h sys/byteorder.h], [break])
 
-# Even if we have byteswap.h, we may lack the specific macros/functions.
-if test x$ac_cv_header_byteswap_h = xyes ; then
-       m4_foreach([FUNC], [bswap_16,bswap_32,bswap_64], [
-               AC_MSG_CHECKING([if FUNC is available])
-               AC_LINK_IFELSE([AC_LANG_SOURCE([
+AC_MSG_CHECKING([if __builtin_bswap16/32/64 are supported])
+AC_LINK_IFELSE([AC_LANG_PROGRAM([[]],
+                       [[__builtin_bswap16(1);
+                       __builtin_bswap32(1);
+                       __builtin_bswap64(1);]])],
+[
+       AC_DEFINE([HAVE___BUILTIN_BSWAPXX], [1],
+               [Define to 1 if the GNU C extensions
+               __builtin_bswap16/32/64 are supported.])
+       AC_MSG_RESULT([yes])
+], [
+       AC_MSG_RESULT([no])
+
+       # Look for other byteswapping methods.
+       AC_CHECK_HEADERS([byteswap.h sys/endian.h sys/byteorder.h], [break])
+
+       # Even if we have byteswap.h we may lack the specific macros/functions.
+       if test x$ac_cv_header_byteswap_h = xyes ; then
+               m4_foreach([FUNC], [bswap_16,bswap_32,bswap_64], [
+                       AC_MSG_CHECKING([if FUNC is available])
+                       AC_LINK_IFELSE([AC_LANG_SOURCE([
 #include <byteswap.h>
 int
 main(void)
@@ -36,28 +51,15 @@ main(void)
        FUNC[](42);
        return 0;
 }
-               ])], [
-                       AC_DEFINE(HAVE_[]m4_toupper(FUNC), [1],
+                       ])], [
+                               AC_DEFINE(HAVE_[]m4_toupper(FUNC), [1],
                                        [Define to 1 if] FUNC [is available.])
-                       AC_MSG_RESULT([yes])
-               ], [AC_MSG_RESULT([no])])
-
-       ])dnl
-fi
+                               AC_MSG_RESULT([yes])
+                       ], [AC_MSG_RESULT([no])])
 
-AC_MSG_CHECKING([if __builtin_bswap16/32/64 are supported])
-AC_LINK_IFELSE([AC_LANG_PROGRAM([[]],
-                       [[__builtin_bswap16(1);
-                       __builtin_bswap32(1);
-                       __builtin_bswap64(1);]])],
-       [
-               AC_DEFINE([HAVE___BUILTIN_BSWAPXX], [1],
-                       [Define to 1 if the GNU C extensions
-                       __builtin_bswap16/32/64 are supported.])
-               AC_MSG_RESULT([yes])
-       ], [
-               AC_MSG_RESULT([no])
-       ])
+               ])dnl
+       fi
+])
 
 AC_MSG_CHECKING([if unaligned memory access should be used])
 AC_ARG_ENABLE([unaligned-access], AS_HELP_STRING([--enable-unaligned-access],