1 files changed, 49 insertions, 0 deletions
diff --git a/ext/bigdecimal/lib/pai.rb b/ext/bigdecimal/lib/pai.rb
new file mode 100644
index 0000000000..4e2dd7104a
--- /dev/null
+++ b/ext/bigdecimal/lib/pai.rb
@@ -0,0 +1,49 @@
+#!/usr/local/bin/ruby
+
+#
+# pai.rb
+#
+
+require "bigdecimal"
+#
+# Calculates 3.1415.... using J. Machin's formula.
+#
+def pai(sig) # sig: Number of significant figures
+  exp    = -sig
+  pi     = BigDecimal::new("0")
+  two    = BigDecimal::new("2")
+  m25    = BigDecimal::new("-0.04")
+  m57121 = BigDecimal::new("-57121")
+
+  u = BigDecimal::new("1")
+  k = BigDecimal::new("1")
+  w = BigDecimal::new("1")
+  t = BigDecimal::new("-80")
+  while (u.exponent >= exp) 
+    t   = t*m25
+    u,r = t.div(k,sig)
+    pi  = pi + u
+    k   = k+two
+  end
+
+  u = BigDecimal::new("1")
+  k = BigDecimal::new("1")
+  w = BigDecimal::new("1")
+  t = BigDecimal::new("956")
+  while (u.exponent >= exp )
+    t,r = t.div(m57121,sig)
+    u,r = t.div(k,sig)
+    pi  = pi + u
+    k   = k+two
+  end
+  pi
+end
+
+if $0 == __FILE__
+  if ARGV.size == 1
+    print "PAI("+ARGV[0]+"):\n"
+    p pai(ARGV[0].to_i)
+  else
+    print "TRY: ruby pai.rb 1000 \n"
+  end
+end