[rtems commit] score: Use builtin for _Bitfield_Find_first_bit()

[Sebastian Huber]

Module:    rtems
Branch:    master
Commit:    80bbb4eda36cf00e13fa49a206b88e80cf2acdc7
Changeset: http://git.rtems.org/rtems/commit/?id=80bbb4eda36cf00e13fa49a206b88e80cf2acdc7

Author:    Sebastian Huber <sebastian.huber at embedded-brains.de>
Date:      Wed Jun  8 08:52:38 2016 +0200

score: Use builtin for _Bitfield_Find_first_bit()

In case the CPU architecture provides no specialized
_CPU_Bitfield_Find_first_bit() macro, then use the __builtin_clz()
builtin in case __GNUC__ is defined.

---

 cpukit/score/include/rtems/score/prioritybitmapimpl.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/cpukit/score/include/rtems/score/prioritybitmapimpl.h b/cpukit/score/include/rtems/score/prioritybitmapimpl.h
index 2041a20..0082720 100644
--- a/cpukit/score/include/rtems/score/prioritybitmapimpl.h
+++ b/cpukit/score/include/rtems/score/prioritybitmapimpl.h
@@ -60,6 +60,8 @@ RTEMS_INLINE_ROUTINE unsigned int _Bitfield_Find_first_bit(
 
 #if ( CPU_USE_GENERIC_BITFIELD_CODE == FALSE )
   _CPU_Bitfield_Find_first_bit( value, bit_number );
+#elif defined(__GNUC__)
+  bit_number = __builtin_clz( value ) - __SIZEOF_INT__ * __CHAR_BIT__ + 16;
 #else
   if ( value < 0x100 ) {
     bit_number = _Bitfield_Leading_zeros[ value ] + 8;