// -*- mode: C++; c-indent-level: 4; c-basic-offset: 4; tab-width: 4 -*-
//
// rt.h: Rcpp R/C++ interface class library -- 
//
// Copyright (C) 2010 - 2011 Douglas Bates, Dirk Eddelbuettel and Romain Francois
//
// This file is part of Rcpp.
//
// Rcpp is free software: you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 2 of the License, or
// (at your option) any later version.
//
// Rcpp is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Rcpp.  If not, see <http://www.gnu.org/licenses/>.

#ifndef Rcpp__stats__random_rt_h
#define Rcpp__stats__random_rt_h

namespace Rcpp {
	namespace stats {

		class TGenerator : public ::Rcpp::Generator<false,double> {
		public:
	
			TGenerator( double df_ ) : df(df_), df_2(df_/2.0) {}
	
			inline double operator()() const {
				/* Some compilers (including MW6) evaluated this from right to left
				   return norm_rand() / sqrt(rchisq(df) / df); */
				double num = norm_rand();
		
				// return num / sqrt(rchisq(df) / df);
				// replaced by the followoing line to skip the test in 
				// rchisq because we already know
				return num / ::sqrt( ::Rf_rgamma(df_2, 2.0) / df);
			}
	
		private:
			double df, df_2 ;
		} ;
	} // stats

	// Please make sure you to read Section 6.3 of "Writing R Extensions"
	// about the need to call GetRNGstate() and PutRNGstate() when using 
	// the random number generators provided by R.
	inline NumericVector rt( int n, double df ){
		// special case
		if (ISNAN(df) || df <= 0.0)
			return NumericVector( n, R_NaN ) ;
	
		// just generating a N(0,1)
		if(!R_FINITE(df))
			return NumericVector( n, norm_rand ) ;
	
		// general case
		return NumericVector( n, stats::TGenerator( df ) ) ;
	}

} // Rcpp

#endif
