nobu	2009-09-24 02:08:37 +0900 (Thu, 24 Sep 2009)

  New Revision: 25062

  http://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=rev&revision=25062

  Log:
    * ext/bigdecimal/lib/bigdecimal/math.rb (atan): reduce loop with
      the formula of the double corner.  based on a patch from
      Masahiro Kanai (CanI) in [ruby-dev:39367].

  Modified files:
    trunk/ChangeLog
    trunk/ext/bigdecimal/lib/bigdecimal/math.rb

Index: ChangeLog
===================================================================
--- ChangeLog	(revision 25061)
+++ ChangeLog	(revision 25062)
@@ -1,3 +1,9 @@
+Thu Sep 24 02:08:35 2009  Nobuyoshi Nakada  <nobu@r...>
+
+	* ext/bigdecimal/lib/bigdecimal/math.rb (atan): reduce loop with
+	  the formula of the double corner.  based on a patch from
+	  Masahiro Kanai (CanI) in [ruby-dev:39367].
+
 Thu Sep 24 01:14:18 2009  Yutaka Kanemoto  <kanemoto@r...>
 
 	* dln.c (aix_loaderror): fixed typo. suppress warnings.
Index: ext/bigdecimal/lib/bigdecimal/math.rb
===================================================================
--- ext/bigdecimal/lib/bigdecimal/math.rb	(revision 25061)
+++ ext/bigdecimal/lib/bigdecimal/math.rb	(revision 25062)
@@ -125,11 +125,14 @@
     if neg = x < 0
       x = -x
     end
-    if x == 1
+    if x.round(prec) == 1
       return pi / (neg ? -4 : 4)
     elsif inv = x > 1
       x = 1 / x
     end
+    if dbl = x > 0.5
+      x = (-1 + sqrt(1 + x**2, prec))/x
+    end
     n    = prec + BigDecimal.double_fig
     y = x
     d = y
@@ -143,6 +146,7 @@
       y += d
       r += 2
     end
+    y *= 2 if dbl
     y = pi / 2 - y if inv
     y = -y if neg
     y

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