1 files changed, 47 insertions, 0 deletions
diff --git a/missing/ffs.c b/missing/ffs.c
new file mode 100644
index 0000000000..9bbb707959
--- /dev/null
+++ b/missing/ffs.c
@@ -0,0 +1,47 @@
+/* ffs.c - find first set bit */
+/* ffs() is defined by POSIX. */
+
+#include "ruby.h"
+
+int ffs(int arg)
+{
+    unsigned int x = (unsigned int)arg;
+    int r = 0;
+
+    if (x == 0)
+        return 0;
+
+#if 32 < SIZEOF_INT * CHAR_BIT
+    if ((x & 0xffffffff) == 0) {
+        x >>= 32;
+        r += 32;
+    }
+#endif
+
+    if ((x & 0xffff) == 0) {
+        x >>= 16;
+        r += 16;
+    }
+
+    if ((x & 0xff) == 0) {
+        x >>= 8;
+        r += 8;
+    }
+
+    if ((x & 0xf) == 0) {
+        x >>= 4;
+        r += 4;
+    }
+
+    if ((x & 0x3) == 0) {
+        x >>= 2;
+        r += 2;
+    }
+
+    if ((x & 0x1) == 0) {
+        x >>= 1;
+        r += 1;
+    }
+
+    return r;
+}