[PATCH 1/5] wined3d: Use __builtin_clz() in wined3d_log2i() when available.

[Henri Verbeet]

---
 configure.ac         |    9 +++++++++
 dlls/wined3d/utils.c |    5 +++++
 2 files changed, 14 insertions(+)

diff --git a/configure.ac b/configure.ac
index 400ee61..2773584 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2595,6 +2595,15 @@ AC_CHECK_FUNCS(\
 )
 LIBS="$ac_save_LIBS"
 
+dnl Check for __builtin_clz
+AC_CACHE_CHECK([for __builtin_clz], ac_cv_have___builtin_clz,
+               AC_LINK_IFELSE([AC_LANG_PROGRAM(,[[return __builtin_clz(1)]])],
+               [ac_cv_have___builtin_clz="yes"], [ac_cv_have___builtin_clz="no"]))
+if test "$ac_cv_have___builtin_clz" = "yes"
+then
+    AC_DEFINE(HAVE___BUILTIN_CLZ, 1, [Define to 1 if you have the `__builtin_clz' built-in function.])
+fi
+
 dnl *** check for the need to define platform-specific symbols
 
 case $host_cpu in
diff --git a/dlls/wined3d/utils.c b/dlls/wined3d/utils.c
index d3fb1d6..566d921 100644
--- a/dlls/wined3d/utils.c
+++ b/dlls/wined3d/utils.c
@@ -3929,8 +3929,12 @@ const struct wine_rb_functions wined3d_ffp_vertex_program_rb_functions =
     wined3d_ffp_vertex_program_key_compare,
 };
 
+/* Return the integer base-2 logarithm of x. Undefined for x == 0. */
 UINT wined3d_log2i(UINT32 x)
 {
+#ifdef HAVE___BUILTIN_CLZ
+    return __builtin_clz(x) ^ 0x1f;
+#else
     static const UINT l[] =
     {
         ~0U, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3,
@@ -3953,6 +3957,7 @@ UINT wined3d_log2i(UINT32 x)
     UINT32 i;
 
     return (i = x >> 16) ? (x = i >> 8) ? l[x] + 24 : l[i] + 16 : (i = x >> 8) ? l[i] + 8 : l[x];
+#endif
 }
 
 const struct blit_shader *wined3d_select_blitter(const struct wined3d_gl_info *gl_info, enum wined3d_blit_op blit_op,
-- 
1.7.10.4