From cd4f59bc5e32c71fcef679ebdbd750c7d2ed5f5e Mon Sep 17 00:00:00 2001
From: nobu <nobu@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Sun, 20 Sep 2009 15:07:38 +0000
Subject: * ext/bigdecimal/lib/bigdecimal/math.rb (sin, cos, atan, exp, log):  
 improved precision and performance.  based on a patch from Makoto   Yamashita
 in [ruby-core:25600] and [ruby-core:25602].

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@25013 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
---
 ext/bigdecimal/lib/bigdecimal/math.rb | 36 ++++++++++++++++++++++++++++++-----
 1 file changed, 31 insertions(+), 5 deletions(-)

(limited to 'ext')

diff --git a/ext/bigdecimal/lib/bigdecimal/math.rb b/ext/bigdecimal/lib/bigdecimal/math.rb
index 24e928b901..635992ef14 100644
--- a/ext/bigdecimal/lib/bigdecimal/math.rb
+++ b/ext/bigdecimal/lib/bigdecimal/math.rb
@@ -49,6 +49,14 @@ module BigMath
     n    = prec + BigDecimal.double_fig
     one  = BigDecimal("1")
     two  = BigDecimal("2")
+    x = -x if neg = x < 0
+    if x > (twopi = two * BigMath.PI(prec))
+      if x > 30
+        x %= twopi
+      else
+        x -= twopi while x > twopi
+      end
+    end
     x1   = x
     x2   = x.mult(x,n)
     sign = 1
@@ -65,7 +73,7 @@ module BigMath
       d   = sign * x1.div(z,m)
       y  += d
     end
-    y
+    neg ? -y : y
   end
 
   # Computes the cosine of x to the specified number of digits of precision.
@@ -77,6 +85,14 @@ module BigMath
     n    = prec + BigDecimal.double_fig
     one  = BigDecimal("1")
     two  = BigDecimal("2")
+    x = -x if x < 0
+    if x > (twopi = two * BigMath.PI(prec))
+      if x > 30
+        x %= twopi
+      else
+        x -= twopi while x > twopi
+      end
+    end
     x1 = one
     x2 = x.mult(x,n)
     sign = 1
@@ -99,11 +115,9 @@ module BigMath
   # Computes the arctangent of x to the specified number of digits of precision.
   #
   # If x is infinite or NaN, returns NaN.
-  # Raises an argument error if x > 1.
   def atan(x, prec)
     raise ArgumentError, "Zero or negative precision for atan" if prec <= 0
     return BigDecimal("NaN") if x.infinite? || x.nan?
-    raise ArgumentError, "x.abs must be less than 1.0" if x.abs>=1
     n    = prec + BigDecimal.double_fig
     y = x
     d = y
@@ -132,6 +146,7 @@ module BigMath
     return BigDecimal("NaN") if x.infinite? || x.nan?
     n    = prec + BigDecimal.double_fig
     one  = BigDecimal("1")
+    x = -x if neg = x < 0
     x1 = one
     y  = one
     d  = y
@@ -145,7 +160,11 @@ module BigMath
       d  = x1.div(z,m)
       y += d
     end
-    y
+    if neg
+      one.div(y, prec)
+    else
+      y.round(prec - y.exponent)
+    end
   end
 
   # Computes the natural logarithm of x to the specified number of digits
@@ -159,6 +178,9 @@ module BigMath
     one = BigDecimal("1")
     two = BigDecimal("2")
     n  = prec + BigDecimal.double_fig
+    if (expo = x.exponent) < 0
+      x = x.mult(BigDecimal("1E#{-expo}"), n)
+    end
     x  = (x - one).div(x + one,n)
     x2 = x.mult(x,n)
     y  = x
@@ -171,7 +193,11 @@ module BigMath
       d  = x.div(i,m)
       y += d
     end
-    y*two
+    y *= two
+    if expo < 0
+      y += log(BigDecimal("10"),prec) * BigDecimal(expo.to_s)
+    end
+    y
   end
 
   # Computes the value of pi to the specified number of digits of precision.
-- 
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