benchmark.find-pi: adding the bignum ratio find-pi benchmark.

extra/benchmark/find-pi/find-pi.factor

@@ -0,0 +1,16 @@
+! Copyright (C) 2012 John Benediktsson
+! See http://factorcode.org/license.txt for BSD license.
+USING: kernel locals math ;
+IN: benchmark.find-pi
+
+:: find-pi-to ( accuracy -- n approx )
+    1 4 [
+        over [ 2 * 1 + ] [ odd? [ neg ] when ] bi
+        4 swap / [ + ] keep
+        abs accuracy >= [ 1 + ] 2dip
+    ] loop ;
+
+: find-pi-benchmark ( -- )
+    0.0005 find-pi-to drop 4001 assert= ;
+
+MAIN: find-pi-benchmark