test for __builtin_clz() and fallback to an inline implementation.

__builtin_clz() is not defined by gcc prior to 3.4 and maybe not for some other
compiler vendors.

Signed-off-by: Uli Schlachter <psychon@znc.in>

awesomeConfig.cmake

@@ -164,7 +164,6 @@ endmacro()
 a_find_library(LIB_EV ev)
 # GNU libc has <execinfo.h> and backtrace() stuff. If this is not available, we
 # need libexecinfo.
-message(STATUS "checking for execinfo")
 try_compile(HAS_EXECINFO
     ${CMAKE_BINARY_DIR}
     ${CMAKE_SOURCE_DIR}/build-tests/execinfo.c)
@@ -183,6 +182,16 @@ else()
     message(STATUS "checking for execinfo -- not found")
 endif()
 
+# __builtin_clz is available since gcc 3.4
+try_compile(HAS___BUILTIN_CLZ
+    ${CMAKE_BINARY_DIR}
+    ${CMAKE_SOURCE_DIR}/build-tests/__builtin_clz.c)
+if(HAS___BUILTIN_CLZ)
+    message(STATUS "checking for __builtin_clz -- yes")
+else()
+    message(STATUS "checking for __builtin_clz -- no")
+endif()
+
 # Error check
 if(NOT LUA51_FOUND AND NOT LUA50_FOUND) # This is a workaround to a cmake bug
     message(FATAL_ERROR "lua library not found")

build-tests/__builtin_clz.c

@@ -0,0 +1,12 @@
+/*
+ * build-tests/__builtin_clz.c
+ *
+ * test if the compiler has __builtin_clz().
+ */
+
+int
+main(void)
+{
+
+	return (__builtin_clz(42));
+}

config.h.in

@@ -7,5 +7,6 @@
 
 #cmakedefine WITH_DBUS
 #cmakedefine HAS_EXECINFO
+#cmakedefine HAS___BUILTIN_CLZ
 
 #endif //_CONFIG_H_

keyresolv.c

@@ -346,7 +346,37 @@ static int8_t const __utf32_clz_to_len[32] = {
     2, 2, 2, 2,         /* 0x00000080 */
     1, 1, 1, 1, 1, 1, 1 /* 0x00000001 */
 };
-#define utf8clen(c) __utf32_clz_to_len[__builtin_clz((uint32_t)(c) | 1)]
+
+#ifdef HAS___BUILTIN_CLZ
+#define a_clz(x) __builtin_clz(x)
+#else
+/*
+ * function stolen from x264/common/osdep.h
+ *
+ * osdep.h: h264 encoder
+ *
+ * Copyright (C) 2007-2008 x264 project
+ *
+ * Authors: Loren Merritt <lorenm@u.washington.edu>
+ *          Laurent Aimar <fenrir@via.ecp.fr>
+ *
+ * GPLv2 or higher.
+ */
+static inline int
+a_clz(uint32_t x)
+{
+    static uint8_t lut[16] = {4,3,2,2,1,1,1,1,0,0,0,0,0,0,0,0};
+    int y, z = (((x >> 16) - 1) >> 27) & 16;
+    x >>= z^16;
+    z += y = ((x - 0x100) >> 28) & 8;
+    x >>= y^8;
+    z += y = ((x - 0x10) >> 29) & 4;
+    x >>= y^4;
+    return z + lut[x];
+}
+#endif
+
+#define utf8clen(c) __utf32_clz_to_len[a_clz((uint32_t)(c) | 1)]
 
 static bool
 keysym_to_utf8(char *buf, const xcb_keysym_t ksym)