Re: [ft-devel] assembler or builtin?

[Werner LEMBERG]

> The proposed patch is attached. It utilizes gcc builtins to optimize
> FT_MSB. FT_CONFIG_OPTION_NO_ASSEMBLER will disable it if necessary.
> Please comment.

LGTM.  I suggest the slightly modified patch as attached.


    Werner

diff --git a/builds/unix/ftconfig.in b/builds/unix/ftconfig.in
index 2cf6708..f22867c 100644
--- a/builds/unix/ftconfig.in
+++ b/builds/unix/ftconfig.in
@@ -569,6 +569,22 @@ FT_BEGIN_HEADER
 
 #endif /* __GNUC__ && __x86_64__ */
 
+#if defined( __GNUC__ )
+#if ( __GNUC__ > 3 ) || ( ( __GNUC__ == 3 ) && ( __GNUC_MINOR__ >= 4 ) )
+
+#if FT_SIZEOF_INT == 4
+
+#define FT_MSB_BUILTIN( x )  ( 31 - __builtin_clz( x ) )  
+
+#elif FT_SIZEOF_LONG == 4
+
+#define FT_MSB_BUILTIN( x )  ( 31 - __builtin_clzl( x ) )  
+
+#endif
+
+#endif
+#endif /* __GNUC__ */
+
 #endif /* !FT_CONFIG_OPTION_NO_ASSEMBLER */
 
 
diff --git a/include/config/ftconfig.h b/include/config/ftconfig.h
index d98a311..98cccc5 100644
--- a/include/config/ftconfig.h
+++ b/include/config/ftconfig.h
@@ -536,6 +536,22 @@ FT_BEGIN_HEADER
 
 #endif /* __GNUC__ && __x86_64__ */
 
+#if defined( __GNUC__ )
+#if ( __GNUC__ > 3 ) || ( ( __GNUC__ == 3 ) && ( __GNUC_MINOR__ >= 4 ) )
+
+#if FT_SIZEOF_INT == (32 / FT_CHAR_BIT)
+
+#define FT_MSB_BUILTIN( x )  ( 31 - __builtin_clz( x ) )  
+
+#elif FT_SIZEOF_LONG == (32 / FT_CHAR_BIT)
+
+#define FT_MSB_BUILTIN( x )  ( 31 - __builtin_clzl( x ) )  
+
+#endif
+
+#endif
+#endif /* __GNUC__ */
+
 #endif /* !FT_CONFIG_OPTION_NO_ASSEMBLER */
 
 
diff --git a/src/base/ftcalc.c b/src/base/ftcalc.c
index 2216880..09168bc 100644
--- a/src/base/ftcalc.c
+++ b/src/base/ftcalc.c
@@ -103,6 +103,12 @@
   FT_BASE_DEF ( FT_Int )
   FT_MSB( FT_UInt32 z )
   {
+#ifdef FT_MSB_BUILTIN
+
+    return FT_MSB_BUILTIN( z );
+
+#else
+
     FT_Int shift = 0;
 
     /* determine msb bit index in `shift' */
@@ -133,6 +139,8 @@
     }
 
     return shift;
+
+#endif /* FT_MSB_BUILTIN */
   }