* time.c (rb_big_abs_find_minbit): use ffs().

* configure.in: check ffs().

* missing/ffs.c: new file.

* include/ruby/missing.h (ffs): declared.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@27759 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

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;
+}