Patch ruby to define tau

tau.patch

diff --git a/ext/bigdecimal/lib/bigdecimal/math.rb b/ext/bigdecimal/lib/bigdecimal/math.rb
index c17841f..c672cbf 100644
--- a/ext/bigdecimal/lib/bigdecimal/math.rb
+++ b/ext/bigdecimal/lib/bigdecimal/math.rb
@@ -9,6 +9,7 @@ require 'bigdecimal'
 #   atan(x, prec)  Note: |x|<1, x=0.9999 may not converge.
 #   exp (x, prec)
 #   log (x, prec)
+#   TAU (prec)
 #   PI  (prec)
 #   E   (prec) == exp(1.0,prec)
 #
@@ -222,6 +223,11 @@ module BigMath
     y
   end
 
+  # See http://tauday.com/
+  def TAU(prec)
+    PI(prec)*BigDecimal("2")
+  end
+
   # Computes the value of pi to the specified number of digits of precision.
   def PI(prec)
     raise ArgumentError, "Zero or negative argument for PI" if prec <= 0
diff --git a/math.c b/math.c
index e3a78f7..e8b2525 100644
--- a/math.c
+++ b/math.c
@@ -775,8 +775,10 @@ Init_Math(void)
 
 #ifdef M_PI
     rb_define_const(rb_mMath, "PI", DBL2NUM(M_PI));
+    rb_define_const(rb_mMath, "TAU", DBL2NUM(M_PI*2.0));
 #else
     rb_define_const(rb_mMath, "PI", DBL2NUM(atan(1.0)*4.0));
+    rb_define_const(rb_mMath, "TAU", DBL2NUM(atan(1.0)*8.0));
 #endif
 
 #ifdef M_E

zzdemo

$ git status -s
 M ext/bigdecimal/lib/bigdecimal/math.rb
 M math.c
$ /usr/local/bin/ruby --version # (after doing make && sudo make install)
ruby 1.9.3dev (2011-06-16 trunk 32123) [x86_64-darwin10.7.0]
$ /usr/local/bin/ruby -r bigdecimal/math -e 'puts Math::TAU, BigMath.TAU(100)'
6.283185307179586
0.62831853071795864769252867665590057683943387987502116419498891846156328125724179972560696506842341359642961730265646057277261767213856E1