From 8c3926aea0d782d28fc42ca8d391ce7ec9533e31 Mon Sep 17 00:00:00 2001
From: nobu <nobu@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Wed, 23 Sep 2009 12:25:20 +0000
Subject: * ext/bigdecimal/lib/bigdecimal/math.rb (atan): refined.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@25057 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
---
 ext/bigdecimal/lib/bigdecimal/math.rb | 11 +++++++++++
 1 file changed, 11 insertions(+)

(limited to 'ext/bigdecimal/lib')

diff --git a/ext/bigdecimal/lib/bigdecimal/math.rb b/ext/bigdecimal/lib/bigdecimal/math.rb
index 2771c77b6f..dbc058b0b3 100644
--- a/ext/bigdecimal/lib/bigdecimal/math.rb
+++ b/ext/bigdecimal/lib/bigdecimal/math.rb
@@ -121,6 +121,15 @@ module BigMath
   def atan(x, prec)
     raise ArgumentError, "Zero or negative precision for atan" if prec <= 0
     return BigDecimal("NaN") if x.infinite? || x.nan?
+    pi = PI(prec)
+    if neg = x < 0
+      x = -x
+    end
+    if x == 1
+      return pi / (neg ? -4 : 4)
+    elsif inv = x > 1
+      x = 1 / x
+    end
     n    = prec + BigDecimal.double_fig
     y = x
     d = y
@@ -134,6 +143,8 @@ module BigMath
       y += d
       r += 2
     end
+    y = pi / 2 - y if inv
+    y = -y if neg
     y
   end
 
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