source: svn/trunk/Utilities/HepMC/src/GenEventStreamIO.cc@ 899

//--------------------------------------------------------------------------
//
// GenEventStreamIO.cc
// Author:  Lynn Garren
//
// Implement operator >> and operator <<
//
// ----------------------------------------------------------------------

#include <iostream>
#include <ostream>
#include <istream>
#include <sstream>

#include "GenEvent.h"
#include "GenCrossSection.h"
#include "StreamInfo.h"
#include "StreamHelpers.h"
#include "Version.h"
#include "IO_Exception.h"

namespace HepMC {

// ------------------------- local methods ----------------

/// This method is called by the stream destructor.
/// It does cleanup on stored user data (StreamInfo)
/// and is registered by the first call to get_stream_info().
void HepMCStreamCallback(std::ios_base::event e, std::ios_base& b, int i)
{
  // only clean up if the stream object is going away.
  if(i!=0 && e!= std::ios_base::erase_event) return;

  // retrieve the pointer to the object
  StreamInfo* hd = (StreamInfo*)b.pword(i);
  b.pword(i) = 0;
  b.iword(i) = 0;
#ifdef HEPMC_DEBUG
  // the following line is just for sanity checking
  if(hd) std::cerr << "deleted StreamInfo " << hd->stream_id() << "\n";
#endif
  delete hd;
}

// ------------------------- iomanip ----------------

/// A custom iomanip that allows us to store and access user data (StreamInfo)
/// associated with the stream.
/// This method creates the StreamInfo object the first time it is called.
template <class IO>
StreamInfo& get_stream_info(IO& iost)
{
  if(iost.iword(0) == 0)
    {
      // make sure we add the callback if this is the first time through
      iost.iword(0)=1;
      iost.register_callback(&HepMCStreamCallback, 0);
      // this is our special "context" record.
      // there is one of these at the head of each IO block.
      // allocate room for a StreamInfo in the userdata area
      iost.pword(0) = new StreamInfo;
#ifdef HEPMC_DEBUG
      // the following line is just for sanity checking
      std::cerr << "created StreamInfo " << ((StreamInfo*)iost.pword(0))->stream_id() << "\n";
#endif
    }
  return *(StreamInfo*)iost.pword(0);
}
        
// ------------------------- GenEvent member functions ----------------

std::ostream& GenEvent::write( std::ostream& os )
{
    /// Writes evt to an output stream.

    //
    StreamInfo & info = get_stream_info(os);
    //
    // if this is the first event, set precision
    if ( !info.finished_first_event() ) {
        // precision 16 (# digits following decimal point) is the minimum that
        //  will capture the full information stored in a double
        //  However, we let the user set precision, since that is the expected functionality
        // we use decimal to store integers, because it is smaller than hex!
        os.setf(std::ios::dec,std::ios::basefield);
        os.setf(std::ios::scientific,std::ios::floatfield);
        //
        info.set_finished_first_event(true);
    }
    //
    // output the event data including the number of primary vertices
    //  and the total number of vertices
    //std::vector<long> random_states = random_states();
    os << 'E';
    detail::output( os, event_number() );
    detail::output( os, mpi() );
    detail::output( os, event_scale() );
    detail::output( os, alphaQCD() );
    detail::output( os, alphaQED() );
    detail::output( os, signal_process_id() );
    detail::output( os,   ( signal_process_vertex() ?
                signal_process_vertex()->barcode() : 0 )   );
    detail::output( os, vertices_size() ); // total number of vertices.
    write_beam_particles( os, beam_particles() );
    // random state
    detail::output( os, (int)m_random_states.size() );
    for ( std::vector<long>::iterator rs = m_random_states.begin(); 
          rs != m_random_states.end(); ++rs ) {
         detail::output( os, *rs );
    }
    // weights
    // we need to iterate over the map so that the weights printed 
    // here will be in the same order as the names printed next
    os << ' ' << (int)weights().size() ;
    for ( WeightContainer::const_map_iterator w = weights().map_begin(); 
          w != weights().map_end(); ++w ) {
        detail::output( os, m_weights[w->second] );
    }
    detail::output( os,'\n');
    // now add names for weights
    // note that this prints a new line if and only if the weight container
    // is not empty
    if ( ! weights().empty() ) {
        os << "N " << weights().size() << " " ;
        for ( WeightContainer::const_map_iterator w = weights().map_begin(); 
              w != weights().map_end(); ++w ) {
            detail::output( os,'"');
            os << w->first;
            detail::output( os,'"');
            detail::output( os,' ');
        }
        detail::output( os,'\n');
    }
    //
    // Units
    os << "U " << name(momentum_unit());
    os << " " << name(length_unit());
    detail::output( os,'\n');
    //
    // write GenCrossSection if it has been set
    if( m_cross_section ) m_cross_section->write(os);
    //
    // write HeavyIon and PdfInfo if they have been set
    if( m_heavy_ion ) os << heavy_ion() ;
    if( m_pdf_info ) os << pdf_info() ;
    //
    // Output all of the vertices - note there is no real order.
    for ( GenEvent::vertex_const_iterator v = vertices_begin();
          v != vertices_end(); ++v ) {
        write_vertex(os, *v);
    }
    return os;
}

std::istream& GenEvent::read( std::istream& is )
{
    /// read a GenEvent from streaming input
    //
    StreamInfo & info = get_stream_info(is);
    clear();
    //
    // search for event listing key before first event only.
    if ( !info.finished_first_event() ) {
        //
        find_file_type(is);
        info.set_finished_first_event(true);
    }
    //
    // make sure the stream is good
    if ( !is ) {
        std::cerr << "streaming input: end of stream found "
                  << "setting badbit." << std::endl;
        is.clear(std::ios::badbit); 
        return is;
    }

    //
    // test to be sure the next entry is of type "E" then ignore it
    if ( is.peek()!='E' ) { 
        // if the E is not the next entry, then check to see if it is
        // the end event listing key - if yes, search for another start key
        int ioendtype;
        find_end_key(is,ioendtype);
        if ( ioendtype == info.io_type() ) {
            find_file_type(is);
            // are we at the end of the file?
            if( !is ) return is;
        } else if ( ioendtype > 0 ) {
            std::cerr << "streaming input: end key does not match start key "
                      << "setting badbit." << std::endl;
            is.clear(std::ios::badbit); 
            return is;
        } else if ( !info.has_key() ) {
            find_file_type(is);
            // are we at the end of the file?
            if( !is ) return is;
        } else {
            std::cerr << "streaming input: end key not found "
                      << "setting badbit." << std::endl;
            is.clear(std::ios::badbit); 
            return is;
        }
    } 

    int signal_process_vertex = 0;
    int num_vertices = 0, bp1 = 0, bp2 = 0;
    // OK - now ready to start reading the event, so set the header flag
    info.set_reading_event_header(true);
    // The flag will be set to false when we reach the end of the header
    while(info.reading_event_header()) {
        switch(is.peek()) {
            case 'E':
            {   // deal with the event line
                process_event_line( is, num_vertices, bp1, bp2, signal_process_vertex );
            } break;
            case 'N':
            {   // get weight names 
                read_weight_names( is );
            } break;
            case 'U':
            {   // get unit information if it exists
                if( info.io_type() == gen ) {
                    read_units( is );
                }
            } break;
            case 'C':
            {   // we have a GenCrossSection line
                // create cross section
                GenCrossSection xs;
                // check for invalid data
                try {
                    // read the line
                    xs.read(is);
                }
                catch (IO_Exception& e) {
                    detail::find_event_end( is );
                }
                if(xs.is_set()) { 
                    set_cross_section( xs );
                }
            } break;
            case 'H':
            {   // we have a HeavyIon line OR an unexpected HepMC... line
                if( info.io_type() == gen || info.io_type() == extascii ) {
                    // get HeavyIon
                    HeavyIon ion;
                    // check for invalid data
                    try {
                        is >> &ion;
                    }
                    catch (IO_Exception& e) {
                        detail::find_event_end( is );
                    }
                    if(ion.is_valid()) { 
                        set_heavy_ion( ion );
                    }
                }
            } break;
            case 'F':
            {   // we have a PdfInfo line
                if( info.io_type() == gen || info.io_type() == extascii ) {
                    // get PdfInfo
                    PdfInfo pdf;
                    // check for invalid data
                    try {
                        is >> &pdf;
                    }
                    catch (IO_Exception& e) {
                        detail::find_event_end( is );
                    }
                    if(pdf.is_valid()) { 
                        set_pdf_info( pdf );
                    }
                }
            } break;
            case 'V':
            {   
                // this should be the first vertex line - exit this loop
                info.set_reading_event_header(false);
            } break;
            case 'P':
            {   // we should not find this line
                std::cerr << "streaming input: found unexpected line P" << std::endl;
                info.set_reading_event_header(false);
            } break;
            default:
                // ignore everything else
                break;
        } // switch on line type
    } // while reading_event_header
    //
    // the end vertices of the particles are not connected until
    //  after the event is read --- we store the values in a map until then
    TempParticleMap particle_to_end_vertex;
    //
    // read in the vertices
    for ( int iii = 1; iii <= num_vertices; ++iii ) {
        GenVertex* v = new GenVertex();
        try {
            detail::read_vertex(is,particle_to_end_vertex,v);
        }
        catch (IO_Exception& e) {
            for( TempParticleMap::orderIterator it = particle_to_end_vertex.order_begin(); 
                 it != particle_to_end_vertex.order_end(); ++it ) {
                GenParticle* p = it->second;
                // delete particles only if they are not already owned by a vertex
                if( p->production_vertex() ) {
                } else if( p->end_vertex() ) {
                } else {
                     delete p;
                }
            }
            delete v;
            detail::find_event_end( is );
        }
        add_vertex( v );
    }
    // set the signal process vertex
    if ( signal_process_vertex ) {
        set_signal_process_vertex( 
            barcode_to_vertex(signal_process_vertex) );
    }
    //
    // last connect particles to their end vertices
    GenParticle* beam1(0);
    GenParticle* beam2(0);
    for ( TempParticleMap::orderIterator pmap 
              = particle_to_end_vertex.order_begin(); 
          pmap != particle_to_end_vertex.order_end(); ++pmap ) {
        GenParticle* p =  pmap->second;
        int vtx = particle_to_end_vertex.end_vertex( p );
        GenVertex* itsDecayVtx = barcode_to_vertex(vtx);
        if ( itsDecayVtx ) itsDecayVtx->add_particle_in( p );
        else {
            std::cerr << "read_io_genevent: ERROR particle points"
                      << " to null end vertex. " <<std::endl;
        }
        // also look for the beam particles
        if( p->barcode() == bp1 ) beam1 = p;
        if( p->barcode() == bp2 ) beam2 = p;
    }
    set_beam_particles(beam1,beam2);
    return is;
}

// ------------------------- operator << and operator >> ----------------

std::ostream & operator << (std::ostream & os, GenEvent & evt)
{
    /// Writes evt to an output stream.
    evt.write(os);
    return os;
}

std::istream & operator >> (std::istream & is, GenEvent & evt)
{
    evt.read(is);
    return is;
}

// ------------------------- set units ----------------

std::istream & set_input_units(std::istream & is, 
                               Units::MomentumUnit mom,
                               Units::LengthUnit len )
{
    //
    StreamInfo & info = get_stream_info(is);
    info.use_input_units( mom, len );
    return is;
}

// ------------------------- begin and end block lines ----------------

std::ostream & write_HepMC_IO_block_begin(std::ostream & os )
{
    //
    StreamInfo & info = get_stream_info(os);

    if( !info.finished_first_event() ) {
    os << "\n" << "HepMC::Version " << versionName();
    os << "\n";
    os << info.IO_GenEvent_Key() << "\n";
    }
    return os;
}

std::ostream & write_HepMC_IO_block_end(std::ostream & os )
{
    //
    StreamInfo & info = get_stream_info(os);

    if( info.finished_first_event() ) {
        os << info.IO_GenEvent_End() << "\n";
        os << std::flush;
    }
    return os;
}

std::istream & GenEvent::process_event_line( std::istream & is, 
                                             int & num_vertices,
                                             int & bp1, int & bp2,
                                             int & signal_process_vertex )
{
    //
    if ( !is ) {
        std::cerr << "GenEvent::process_event_line setting badbit." << std::endl;
        is.clear(std::ios::badbit);
        return is;
    } 
    //
    StreamInfo & info = get_stream_info(is);
    std::string line;
    std::getline(is,line);
    std::istringstream iline(line);
    std::string firstc;
    iline >> firstc;
    //
    // read values into temp variables, then fill GenEvent
    int event_number = 0, signal_process_id = 0,
        random_states_size = 0, nmpi = -1;
    double eventScale = 0, alpha_qcd = 0, alpha_qed = 0;
    iline >> event_number;
    if(!iline) detail::find_event_end( is );
    if( info.io_type() == gen || info.io_type() == extascii ) {
        iline >> nmpi;
        if(!iline) detail::find_event_end( is );
        set_mpi( nmpi );
    }
    iline >> eventScale ;
    if(!iline) detail::find_event_end( is );
    iline >> alpha_qcd ;
    if(!iline) detail::find_event_end( is );
    iline >> alpha_qed;
    if(!iline) detail::find_event_end( is );
    iline >> signal_process_id ;
    if(!iline) detail::find_event_end( is );
    iline >> signal_process_vertex;
    if(!iline) detail::find_event_end( is );
    iline >> num_vertices;
    if(!iline) detail::find_event_end( is );
    if( info.io_type() == gen || info.io_type() == extascii ) {
        iline >> bp1 ;
        if(!iline) detail::find_event_end( is );
        iline >> bp2;
        if(!iline) detail::find_event_end( is );
    }
    iline >> random_states_size;
    if(!iline) detail::find_event_end( is );
    std::vector<long> random_states(random_states_size);
    for ( int i = 0; i < random_states_size; ++i ) {
        iline >> random_states[i];
        if(!iline) detail::find_event_end( is );
    }
    WeightContainer::size_type weights_size = 0;
    iline >> weights_size;
    if(!iline) detail::find_event_end( is );
    std::vector<double> wgt(weights_size);
    for ( WeightContainer::size_type ii = 0; ii < weights_size; ++ii ) {
        iline >> wgt[ii];
        if(!iline) detail::find_event_end( is );
    }
    // weight names will be added later if they exist
    if( weights_size > 0 ) m_weights = wgt;
    // 
    // fill signal_process_id, event_number, random_states, etc.
    set_signal_process_id( signal_process_id );
    set_event_number( event_number );
    set_random_states( random_states );
    set_event_scale( eventScale );
    set_alphaQCD( alpha_qcd );
    set_alphaQED( alpha_qed );
    //
    return is;
}

std::istream & GenEvent::read_weight_names( std::istream & is )
{
    // now check for a named weight line
    if ( !is ) {
        std::cerr << "GenEvent::read_weight_names setting badbit." << std::endl;
        is.clear(std::ios::badbit);
        return is;
    } 
    // Test to be sure the next entry is of type "N"
    // If we have no named weight line, this is not an error
    // releases prior to 2.06.00 do not have named weights
    if ( is.peek() !='N') {
        return is;
    } 
    // now get this line and process it
    std::string line;
    std::getline(is,line);
    std::istringstream wline(line);
    std::string firstc;
    WeightContainer::size_type name_size = 0;
    wline >> firstc >> name_size;
    if(!wline) detail::find_event_end( is );
    if( firstc != "N") { 
        std::cout << "debug: first character of named weights is " << firstc << std::endl;
        std::cout << "debug: We should never get here" << std::endl;
        is.clear(std::ios::badbit);
        return is;
    }
    if( m_weights.size() != name_size ) { 
        std::cout << "debug: weight sizes do not match "<< std::endl;
        std::cout << "debug: weight vector size is " << m_weights.size() << std::endl;
        std::cout << "debug: weight name size is " << name_size << std::endl;
        is.clear(std::ios::badbit);
        return is;
    }
    std::string name;
    std::string::size_type i1 = line.find("\"");
    std::string::size_type i2;
    std::string::size_type len = line.size();
    WeightContainer namedWeight;
    for ( WeightContainer::size_type ii = 0; ii < name_size; ++ii ) {
        // weight names may contain blanks
        if(i1 >= len) {
            std::cout << "debug: attempting to read past the end of the named weight line " << std::endl;
            std::cout << "debug: We should never get here" << std::endl;
            std::cout << "debug: Looking for the end of this event" << std::endl;
            detail::find_event_end( is );
        }
        i2 = line.find("\"",i1+1);
        name = line.substr(i1+1,i2-i1-1);
        namedWeight[name] = m_weights[ii];
        i1 = line.find("\"",i2+1);
    }
    m_weights = namedWeight;
    return is;
}

std::istream & GenEvent::read_units( std::istream & is )
{
    //
    if ( !is ) {
        std::cerr << "GenEvent::read_units setting badbit." << std::endl;
        is.clear(std::ios::badbit);
        return is;
    } 
    //
    StreamInfo & info = get_stream_info(is);
    // test to be sure the next entry is of type "U" then ignore it
    // if we have no units, this is not an error
    // releases prior to 2.04.00 did not write unit information
    if ( is.peek() !='U') {
        use_units( info.io_momentum_unit(), 
                       info.io_position_unit() );
        return is;
    } 
    is.ignore();        // ignore the first character in the line
    std::string mom, pos;
    is >> mom >> pos;
    is.ignore(1);      // eat the extra whitespace
    use_units(mom,pos);
    //
    return is;
}

std::istream & GenEvent::find_file_type( std::istream & istr )
{
    //
    // make sure the stream is good
    if ( !istr ) return istr;

    //
    StreamInfo & info = get_stream_info(istr);

    // if there is no input block line, then we assume this stream
    // is in the IO_GenEvent format
    if ( istr.peek()=='E' ) {
        info.set_io_type( gen );
        info.set_has_key(false);
        return istr;
    }
    
    std::string line;
    while ( std::getline(istr,line) ) {
        //
        // search for event listing key before first event only.
        //
        if( line == info.IO_GenEvent_Key() ) {
            info.set_io_type( gen );
            info.set_has_key(true);
            return istr;
        } else if( line == info.IO_Ascii_Key() ) {
            info.set_io_type( ascii );
            info.set_has_key(true);
            return istr;
        } else if( line == info.IO_ExtendedAscii_Key() ) {
            info.set_io_type( extascii );
            info.set_has_key(true);
            return istr;
        } else if( line == info.IO_Ascii_PDT_Key() ) {
            info.set_io_type( ascii_pdt );
            info.set_has_key(true);
            return istr;
        } else if( line == info.IO_ExtendedAscii_PDT_Key() ) {
            info.set_io_type( extascii_pdt );
            info.set_has_key(true);
            return istr;
        }
    }
    info.set_io_type( 0 );
    info.set_has_key(false);
    return istr;
}

std::istream & GenEvent::find_end_key( std::istream & istr, int & iotype )
{
    iotype = 0;
    // peek at the first character before proceeding
    if( istr.peek()!='H' ) return istr;
    //
    // we only check the next line
    std::string line;
    std::getline(istr,line);
    //
    StreamInfo & info = get_stream_info(istr);
    //
    // check to see if this is an end key
    if( line == info.IO_GenEvent_End() ) {
        iotype = gen;
    } else if( line == info.IO_Ascii_End() ) {
        iotype = ascii;
    } else if( line == info.IO_ExtendedAscii_End() ) {
        iotype = extascii;
    } else if( line == info.IO_Ascii_PDT_End() ) {
        iotype = ascii_pdt;
    } else if( line == info.IO_ExtendedAscii_PDT_End() ) {
        iotype = extascii_pdt;
    }
    if( iotype != 0 && info.io_type() != iotype ) {
        std::cerr << "GenEvent::find_end_key: iotype keys have changed" << std::endl;
    } else {
        return istr;
    }
    //
    // if we get here, then something has gotten badly confused
    std::cerr << "GenEvent::find_end_key: MALFORMED INPUT" << std::endl;
    istr.clear(std::ios::badbit); 
    return istr;
}

std::ostream & establish_output_stream_info( std::ostream & os )
{
    StreamInfo & info = get_stream_info(os);
    if ( !info.finished_first_event() ) {
        // precision 16 (# digits following decimal point) is the minimum that
        //  will capture the full information stored in a double
        os.precision(16);
        // we use decimal to store integers, because it is smaller than hex!
        os.setf(std::ios::dec,std::ios::basefield);
        os.setf(std::ios::scientific,std::ios::floatfield);
    }
    return os;
}

std::istream & establish_input_stream_info( std::istream & is )
{
    StreamInfo & info = get_stream_info(is);
    if ( !info.finished_first_event() ) {
        // precision 16 (# digits following decimal point) is the minimum that
        //  will capture the full information stored in a double
        is.precision(16);
        // we use decimal to store integers, because it is smaller than hex!
        is.setf(std::ios::dec,std::ios::basefield);
        is.setf(std::ios::scientific,std::ios::floatfield);
    }
    return is;
}


// ------------------------- helper functions ----------------

namespace detail {

// The functions defined here need to use get_stream_info

std::istream & read_particle( std::istream & is, 
                              TempParticleMap & particle_to_end_vertex, 
                              GenParticle * p )
{
    // get the next line
    std::string line;
    std::getline(is,line);
    std::istringstream iline(line);
    std::string firstc;
    iline >> firstc;
    if( firstc != "P" ) { 
        std::cerr << "StreamHelpers::detail::read_particle invalid line type: " 
                  << firstc << std::endl;
        std::cerr << "StreamHelpers::detail::read_particle setting badbit." 
                  << std::endl;
        is.clear(std::ios::badbit); 
        return is;
    } 
    //
    StreamInfo & info = get_stream_info(is);
    //testHepMC.cc
    // declare variables to be read in to, and read everything except flow
    double px = 0., py = 0., pz = 0., e = 0., m = 0., theta = 0., phi = 0.;
    int bar_code = 0, id = 0, status = 0, end_vtx_code = 0, flow_size = 0;
    // check that the input stream is still OK after reading item
    iline >> bar_code ;
    if(!iline) {  delete p; throw IO_Exception("read_particle input stream encounterd invalid data"); }
    iline >> id ;
    if(!iline) {  delete p; throw IO_Exception("read_particle input stream encounterd invalid data"); }
    iline >> px ;
    if(!iline) {  delete p; throw IO_Exception("read_particle input stream encounterd invalid data"); }
    iline >> py ;
    if(!iline) {  delete p; throw IO_Exception("read_particle input stream encounterd invalid data"); }
    iline >> pz ;
    if(!iline) {  delete p; throw IO_Exception("read_particle input stream encounterd invalid data"); }
    iline >> e ;
    if(!iline) {  delete p; throw IO_Exception("read_particle input stream encounterd invalid data"); }
    if( info.io_type() != ascii ) {
        iline >> m ;
        if(!iline) {  delete p; throw IO_Exception("read_particle input stream encounterd invalid data"); }
    }
    iline >> status ;
    if(!iline) {  delete p; throw IO_Exception("read_particle input stream encounterd invalid data"); }
    iline >> theta ;
    if(!iline) {  delete p; throw IO_Exception("read_particle input stream encounterd invalid data"); }
    iline >> phi ;
    if(!iline) {  delete p; throw IO_Exception("read_particle input stream encounterd invalid data"); }
    iline >> end_vtx_code ;
    if(!iline) {  delete p; throw IO_Exception("read_particle input stream encounterd invalid data"); }
    iline >> flow_size;
    if(!iline) {  delete p; throw IO_Exception("read_particle input stream encounterd invalid data"); }
    //
    // read flow patterns if any exist
    Flow flow;
    int code_index, code;
    for ( int i = 1; i <= flow_size; ++i ) {
        iline >> code_index >> code;
        if(!iline) {  delete p; throw IO_Exception("read_particle input stream encounterd invalid data"); }
        flow.set_icode( code_index,code);
    }
    p->set_momentum( FourVector(px,py,pz,e) );
    p->set_pdg_id( id );
    p->set_status( status );
    p->set_flow( flow );
    p->set_polarization( Polarization(theta,phi) );
    if( info.io_type() == ascii ) {
        p->set_generated_mass( p->momentum().m() );
    } else {
        p->set_generated_mass( m );
    }
    p->suggest_barcode( bar_code );
    //
    // all particles are connected to their end vertex separately 
    // after all particles and vertices have been created - so we keep
    // a map of all particles that have end vertices
    if ( end_vtx_code != 0 ) {
        particle_to_end_vertex.addEndParticle(p,end_vtx_code);
    }
    return is;
}

std::istream & read_units( std::istream & is, GenEvent & evt )
{
    //
    if ( !is ) {
        std::cerr << "StreamHelpers read_units setting badbit." << std::endl;
        is.clear(std::ios::badbit);
        return is;
    } 
    //
    StreamInfo & info = get_stream_info(is);
    // test to be sure the next entry is of type "U" then ignore it
    // if we have no units, this is not an error
    // releases prior to 2.04.00 did not write unit information
    if ( is.peek() !='U') {
        evt.use_units( info.io_momentum_unit(), 
                       info.io_position_unit() );
        return is;
    } 
    is.ignore();        // ignore the first character in the line
    std::string mom, pos;
    is >> mom >> pos;
    is.ignore(1);      // eat the extra whitespace
    evt.use_units(mom,pos);
    //
    return is;
}

std::ostream & establish_output_stream_info( std::ostream & os )
{
    StreamInfo & info = get_stream_info(os);
    if ( !info.finished_first_event() ) {
        // precision 16 (# digits following decimal point) is the minimum that
        //  will capture the full information stored in a double
        os.precision(16);
        // we use decimal to store integers, because it is smaller than hex!
        os.setf(std::ios::dec,std::ios::basefield);
        os.setf(std::ios::scientific,std::ios::floatfield);
    }
    return os;
}

std::istream & establish_input_stream_info( std::istream & is )
{
    StreamInfo & info = get_stream_info(is);
    if ( !info.finished_first_event() ) {
        // precision 16 (# digits following decimal point) is the minimum that
        //  will capture the full information stored in a double
        is.precision(16);
        // we use decimal to store integers, because it is smaller than hex!
        is.setf(std::ios::dec,std::ios::basefield);
        is.setf(std::ios::scientific,std::ios::floatfield);
    }
    return is;
}

} // detail

} // HepMC