TRandomAdaptor.cc

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#include "IOMC/RandomEngine/interface/TRandomAdaptor.h"
#include "FWCore/Utilities/interface/EDMException.h"

#include "CLHEP/Random/engineIDulong.h"

#include "TBufferFile.h"

#include <cstddef>
#include <iomanip>
#include <iostream>
#include <sstream>
#include <cstdint>
#include <string>

namespace edm {

  TRandomAdaptor::TRandomAdaptor() : trand_(new TRandom3()) { theSeed = trand_->GetSeed(); }
  TRandomAdaptor::TRandomAdaptor(long seed) : trand_(new TRandom3(seed)) { theSeed = trand_->GetSeed(); }
  TRandomAdaptor::TRandomAdaptor(int rowIndex, int colIndex) : trand_(new TRandom3(rowIndex * colIndex - 1)) {
    theSeed = trand_->GetSeed();
  }

  TRandomAdaptor::TRandomAdaptor(std::istream&) {
    Grumble(std::string("Cannot instantiate a TRandom engine from an istream"));
  }

  TRandomAdaptor::~TRandomAdaptor() {}

  std::ostream& TRandomAdaptor::put(std::ostream& os) const {
    Grumble(std::string("put(std::ostream) not available for TRandom engines"));
    return os;
  }

  std::vector<unsigned long> TRandomAdaptor::put() const {
    std::vector<unsigned long> v;

    int32_t itemSize = sizeof(uint32_t);
    TBufferFile buffer(TBuffer::kWrite, 2048 * itemSize);
    trand_->Streamer(buffer);
    buffer.SetReadMode();
    char* bufferPtr = buffer.Buffer();
    int32_t numItems = (buffer.Length() + itemSize - 1) / itemSize;
    v.reserve(numItems + 1);
    v.push_back(CLHEP::engineIDulong<TRandomAdaptor>());
    for (int i = 0; i < numItems; ++i) {
      // Here we do some ugly manipulations to the data to match the format
      // of the output of the CLHEP put function (the whole point of this adaptor
      // is to make TRandom3 work through the CLHEP interface as if it were a
      // a CLHEP engine ...).  In CLHEP, the vector returned by put contains
      // unsigned long's, but these always contain only 32 bits of information.
      // In the case of a 64 bit build the top 32 bits is only padding (all 0's).

      // Get the next 32 bits of data from the buffer
      uint32_t value32 = *reinterpret_cast<uint32_t*>(bufferPtr + i * itemSize);

      if (i == numItems - 1) {
        int nBytes = buffer.Length() % itemSize;
        if (nBytes == 1)
          value32 &= 0xffu;
        else if (nBytes == 2)
          value32 &= 0xffffu;
        else if (nBytes == 3)
          value32 &= 0xffffffu;
      }

      // Push it into the vector in an unsigned long which may be 32 or 64 bits
      v.push_back(static_cast<unsigned long>(value32));
    }
    return v;
  }

  void TRandomAdaptor::setSeed(long seed, int) {
    trand_->SetSeed(seed);
    theSeed = trand_->GetSeed();
  }

  // Sets the state of the algorithm according to the zero terminated
  // array of seeds. It is allowed to ignore one or many seeds in this array.
  void TRandomAdaptor::setSeeds(long const* seeds, int) {
    trand_->SetSeed(seeds[0]);
    theSeed = trand_->GetSeed();
  }

  std::istream& TRandomAdaptor::get(std::istream& is) {
    Grumble(std::string("get(std::istream) not available for TRandom engines"));
    return getState(is);
  }

  std::istream& TRandomAdaptor::getState(std::istream& is) {
    Grumble(std::string("getState(std::istream) not available for TRandom engines"));
    return is;
  }

  bool TRandomAdaptor::get(std::vector<unsigned long> const& v) {
    if (v.empty())
      return false;
    if (v[0] != CLHEP::engineIDulong<TRandomAdaptor>())
      return false;
    int32_t numItems = v.size() - 1;

    int32_t itemSize = sizeof(uint32_t);
    TBufferFile buffer(TBuffer::kRead, numItems * itemSize + 1024);
    char* bufferPtr = buffer.Buffer();
    for (int32_t i = 0; i < numItems; ++i) {
      *reinterpret_cast<uint32_t*>(bufferPtr + i * itemSize) = static_cast<uint32_t>(v[i + 1] & 0xffffffff);
    }

    // Note that this will fail if the TRandom3 version (specifically the TStreamerInfo)
    // has changed between the time the state was saved and the time the following call
    // is made.  Because we are manually calling the Streamer function, the original
    // TStreamerInfo is not saved anywhere. Normally ROOT saves the TStreamerInfo
    // automatically.
    trand_->Streamer(buffer);

    return true;
  }

  void TRandomAdaptor::Grumble(std::string const& errortext) const {
    // Throw an edm::Exception for unimplemented functions
    std::ostringstream sstr;
    sstr << "Unimplemented Feature: " << errortext << '\n';
    edm::Exception except(edm::errors::UnimplementedFeature, sstr.str());
    throw except;
  }

}  // namespace edm