EvtDiLog.cpp
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EvtDiLog.cpp
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	// $Id: EvtDiLog.cpp,v 1.3 2009-03-16 15:52:42 robbep Exp $
	// Include files

	// local
	#include "EvtGenBase/EvtDiLog.hh"

	#include <cmath>

	//-----------------------------------------------------------------------------
	// Implementation file for class : EvtDiLog
	//
	// 2007-01-23 : Patrick Robbe
	//-----------------------------------------------------------------------------

	double EvtDiLog::DiLog( double x ) {

	double h , t , y , s , a , alfa , b0, b1, b2 ;
	if ( x == 1. ) h = PI6 ;
	else if ( x == -1. ) h = -PI12 ;
	else {
	t = -x ;
	if ( t <= -2. ) {
	y = -1./(1.+t) ;
	s = 1. ;
	a = -PI3 + HF * ( std::pow( log(-t) , 2 ) -
	std::pow( log( 1. + 1./t ) , 2 ) ) ;
	} else if ( t < -1. ) {
	y = -1. - t ;
	s = -1. ;
	a = log( -t ) ;
	a = -PI6 + a * ( a + log( 1. + 1./t ) ) ;
	} else if ( t <= -HF ) {
	y = - (1. + t ) / t ;
	s = 1. ;
	a = log( -t ) ;
	a = -PI6 + a * ( -HF * a + log( 1. + t ) ) ;
	} else if ( t < 0 ) {
	y = -t / ( 1. + t ) ;
	s = -1. ;
	a = HF * std::pow( log( 1. + t ) , 2 ) ;
	} else if ( t <= 1. ) {
	y = t ;
	s = 1. ;
	a = 0. ;
	} else {
	y = 1. / t ;
	s = -1. ;
	a = PI6 + HF * std::pow( log( t ) , 2 ) ;
	}

	h = y + y - 1. ;
	alfa = h + h ;
	b1 = 0. ;
	b2 = 0. ;
	for ( int i = 19 ; i >= 0 ; --i ) {
	b0 = C[ i ] + alfa * b1 - b2 ;
	b2 = b1 ;
	b1 = b0 ;
	}

	h = -(s * ( b0 -h * b2 ) + a ) ;
	}

	return h ;
	}