(un)likely: use __builtin_expect to inform expected path

Remove also unnecessary comparison in getdata nth_field().

Signed-off-by: Sami Kerola <kerolasa@iki.fi>

configure.ac

@@ -69,6 +69,20 @@ AC_CHECK_FUNCS([\
 	strrchr \
 ])
 
+AC_MSG_CHECKING([if the compiler supports __builtin_expect])
+AC_TRY_COMPILE(, [
+    return __builtin_expect(1, 1) ? 1 : 0
+], [
+    have_builtin_expect=yes
+    AC_MSG_RESULT([yes])
+], [
+    have_builtin_expect=no
+    AC_MSG_RESULT([no])
+])
+if test x$have_builtin_expect = xyes ; then
+    AC_DEFINE([HAVE_BUILTIN_EXPECT], [1], [Define to 1 if the compiler supports __builtin_expect.])
+fi
+
 AC_CONFIG_FILES([Makefile
 		 lib/Makefile
 		 man/Makefile

src/dhcpd-pools.h

@@ -93,6 +93,14 @@ inline char *prog_inv_sh_nm_from_file(char *f, char stripext)
 #  endif
 #endif
 
+#ifdef HAVE_BUILTIN_EXPECT
+# define likely(x)	__builtin_expect(!!(x), 1)
+# define unlikely(x)	__builtin_expect(!!(x), 0)
+#else
+# define likely(x)	(x)
+# define unlikely(x)	(x)
+#endif
+
 /* Structures and unions */
 struct configuration_t {
 	char *dhcpdconf_file;

src/getdata.c

@@ -175,7 +175,7 @@ void nth_field(char *restrict dest, const char *restrict src)
 	len = strlen(src);
 	for (i = 0; i < len; i++) {
 		dest[i] = src[i];
-		if (src[i] == ' ' || dest[i] == '\0') {
+		if (unlikely(src[i] == ' ')) {
 			dest[i] = '\0';
 			break;
 		}
@@ -233,7 +233,7 @@ void parse_config(int is_include, const char *restrict config_file,
 #endif				/* POSIX_FADV_SEQUENTIAL */
 
 	/* Very hairy stuff begins. */
-	while (!feof(dhcpd_config)) {
+	while (unlikely(!feof(dhcpd_config))) {
 		c = fgetc(dhcpd_config);
 		/* Certain characters are magical */
 		switch (c) {

src/other.c

@@ -55,7 +55,7 @@ int
 	int i;
 	/* two spaces are very common in lease file, after them
 	 * nearly everything differs */
-	if (a[2] != b[2]) {
+	if (likely(a[2] != b[2])) {
 		return false;
 	}
 	/* "  binding state " == 16 chars, this will skip right