[vlc-commits] vlc_common: add ctz() to count trailing zeroes

[Rémi Denis-Courmont]

vlc | branch: master | Rémi Denis-Courmont <remi at remlab.net> | Sun Jan 13 19:54:59 2013 +0200| [82fdabda9df936231519720e055c7033d5a209b0] | committer: Rémi Denis-Courmont

vlc_common: add ctz() to count trailing zeroes

> http://git.videolan.org/gitweb.cgi/vlc.git/?a=commit;h=82fdabda9df936231519720e055c7033d5a209b0
---

 include/vlc_common.h |   20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/include/vlc_common.h b/include/vlc_common.h
index d09bf78..6a3dd9b 100644
--- a/include/vlc_common.h
+++ b/include/vlc_common.h
@@ -524,7 +524,7 @@ static inline unsigned clz (unsigned x)
 
     while (x)
     {
-        x = x >> 1;
+        x >>= 1;
         i--;
     }
     return i;
@@ -536,6 +536,24 @@ static inline unsigned clz (unsigned x)
 /* XXX: this assumes that int is 32-bits or more */
 #define clz32( x ) (clz(x) - ((sizeof(unsigned) - sizeof (uint32_t)) * 8))
 
+/** Count trailing zeroes */
+VLC_USED
+static inline unsigned ctz (unsigned x)
+{
+#if VLC_GCC_VERSION(3,4)
+    return __builtin_ctz (x);
+#else
+    unsigned i = sizeof (x) * 8;
+
+    while (x)
+    {
+        x <<= 1;
+        i--;
+    }
+    return i;
+#endif
+}
+
 /** Bit weight */
 VLC_USED
 static inline unsigned popcount (unsigned x)