BootstrapGeneratorAlg.cxx

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/*
    Copyright (C) 2002-2023 CERN for the benefit of the ATLAS collaboration
*/

 
#include <AsgAnalysisAlgorithms/BootstrapGeneratorAlg.h>
#include <AsgDataHandles/ReadHandle.h>
#include <AsgDataHandles/WriteDecorHandle.h>
 
std::uint64_t CP::BootstrapGenerator::fnv1a_64(const void *buffer, size_t size, std::uint64_t offset_basis) {
  std::uint64_t h = offset_basis;
  const unsigned char *p = static_cast<const unsigned char *>(buffer);
  for (size_t i = 0; i < size; i++) {
    h ^= p[i];
    h *= m_prime;
  }
  return h;
}
 
std::uint64_t CP::BootstrapGenerator::generateSeed(std::uint64_t eventNumber, std::uint32_t runNumber, std::uint32_t mcChannelNumber)
{
  std::uint64_t hash = fnv1a_64(&runNumber, sizeof(runNumber), m_offset);
  hash = fnv1a_64(&eventNumber, sizeof(eventNumber), hash);
  hash = fnv1a_64(&mcChannelNumber, sizeof(mcChannelNumber), hash);
  return hash;
}
 
void CP::BootstrapGenerator::setSeed(std::uint64_t eventNumber, std::uint32_t runNumber, std::uint32_t mcChannelNumber)
{
  std::uint64_t seed = generateSeed(eventNumber, runNumber, mcChannelNumber);
  m_rng.SetSeed(seed);
}
 
StatusCode CP::BootstrapGeneratorAlg::initialize()
{
  if (m_nReplicas < 0)
    {
      ANA_MSG_ERROR("The number of bootstrapped weights (toys) cannot be negative!");
      return StatusCode::FAILURE;
    }
 
  ANA_CHECK(m_eventInfoKey.initialize());
  ANA_CHECK(m_decorationKey.initialize());
 
  return StatusCode::SUCCESS;
}
 
StatusCode CP::BootstrapGeneratorAlg::execute(const EventContext& ctx) const
{
  SG::ReadHandle<xAOD::EventInfo> evtInfo(m_eventInfoKey, ctx);
  ANA_CHECK(evtInfo.isValid());
 
  // generate a unique seed from runNumber, eventNumber and DSID!
  BootstrapGenerator bootstrap;
  bootstrap.setSeed(evtInfo->eventNumber(), evtInfo->runNumber(), m_data ? 0 : evtInfo->mcChannelNumber());
 
  // and fill it with Poisson(1)
  std::vector<std::uint8_t> weights(m_nReplicas);
  for (std::uint8_t& weight : weights)
    {
      weight = bootstrap.getBootstrap();
    }
 
  // decorate weights onto EventInfo
  SG::WriteDecorHandle<xAOD::EventInfo, std::vector<std::uint8_t>> dec(m_decorationKey, ctx);
  dec(*evtInfo) = std::move(weights);
 
  return StatusCode::SUCCESS;
}