Tau in Ruby

Inspired by http://bugs.python.org/issue12345 and of course The Tau Manifesto, here is a patch for ruby to define tau, the true circle constant.

	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

view raw tau.patch hosted with ❤ by GitHub

	$ 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

view raw zzdemo hosted with ❤ by GitHub

Of course we don't need to really need to patch ruby to get this functionality (but I had fun doing it anyway).

Here is tau.rb so you can just require 'tau'. (Maybe this should be a gem...)

	# See http://tauday.com/
	module Math
	TAU = PI * 2.0
	end
	if defined? BigMath
	module BigMath
	module_function
	def TAU(prec)
	PI(prec) * BigDecimal("2")
	end
	end
	end

view raw tau.rb hosted with ❤ by GitHub

	$ ruby -I. -r bigdecimal/math -r tau -e 'puts Math::TAU, BigMath.TAU(100)'
	6.283185307179586
	0.62831853071795864769252867665590057683943387987502116419498891846156328125724179972560696506842341359642961730265646057277261767213856E1

view raw zzdemo hosted with ❤ by GitHub

Ps, I just learned about module_function.

Update 1: I made this ticket which has been mostly ignored.


Update 2: Ticket has been noticed and discussed! :) Ticket has been categorised as joke! :(


Update 3: Some active debate is going on now and the ticket is now 'assigned'! :) See the details.


Update 4: (28-Jun-2014) Made a pull request in Github.


Update 5: See https://github.com/jneen/math-tau/