ffs: handle 0 argument (bug #8968)

Handle an argument of 0 in ffs(), instead of looping indefinitely.
Add an ffs prototype to dix.h, and add includes to ffs.c.
(cherry picked from 34164e551e4c3909322d50b09835ca4ac1d49d68 commit)

1 files changed, 2 insertions, 0 deletions

diff --git a/dix/ffs.c b/dix/ffs.c
index f84f7b47f..b75657d29 100644
--- a/dix/ffs.c
+++ b/dix/ffs.c
@@ -36,6 +36,8 @@ int
 ffs(int i)
 {
     int j;
+    if (i == 0)
+        return 0;
     for (j = 1; (i & 1) == 0; j++)
 	i >>= 1;
     return j;