Added ffs().

git-svn-id: file:///srv/svn/repos/haiku/trunk/current@11614 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/posix/string.h

@@ -77,6 +77,8 @@ extern const char	*strsignal(int signal);
 #define bcopy(source, dest, length) memcpy((dest), (source), (length))
 #define bzero(buffer, length) memset((buffer), 0, (length))
 
+extern int ffs(int i);
+
 #ifdef __cplusplus
 }
 #endif

src/kernel/libroot/posix/string/ffs.cpp

@@ -0,0 +1,24 @@
+/*
+ * Copyright 2005, Ingo Weinhold, [email protected].
+ * Distributed under the terms of the MIT License.
+ */
+
+#include <strings.h>
+
+// find first (least significant) set bit
+int
+ffs(int value)
+{
+	if (!value)
+		return 0;
+
+	// ToDo: This can certainly be optimized (e.g. by binary search). Or not
+	// unlikely there's a single assembler instruction...
+	for (int i = 1; i <= (int)sizeof(value) * 8; i++, value >>= 1) {
+		if (value & 1)
+			return i;
+	}
+
+	// never gets here
+	return 0;
+}