get_bits.cxx

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/*
   Copyright (C) 2002-2025 CERN for the benefit of the ATLAS collaboration
 */
 
#include "src/get_bits.h"
#include "Identifier/Range.h"
#include "IdDict/IdDictRegion.h"
#include "IdDict/IdDictRange.h"
#include "IdDict/IdDictFieldImplementation.h"
 
namespace IdDict {
  typedef std::vector <IdDictRegion*> RV;
 
  void
  compute_bits(const RV& regions, size_t level, const std::string& group) {
    Range::field ored_field;
    unsigned int k;
    for (k = 0; k < regions.size(); ++k) {
      IdDictRegion* region = regions[k];
      if (region->fieldSize() <= level) continue;
      const IdDictFieldImplementation& f = region->implementation(level);
      const Range::field thisField = f.field();
      //on first time, set the original field
      if (k == 0) ored_field = thisField;
      //on subsequent iterations, 'or' the new fields with the original
      else ored_field |= thisField;
    }
    //
    // Now that we have the ored width of all first fields of
    // all regions, we upgrade the bit width in the corresponding
    // field implementations.
    //
    for (k = 0; k < regions.size(); ++k) {
      IdDictRegion* region = regions[k];
      if (region->fieldSize() <= level) continue;
      // Don't set ored bits for regions outside of group - ok to
      // calculate with them only
      if (group != region->m_group) continue;
      IdDictFieldImplementation& f = region->m_implementation[level];
      f.set_ored_field(ored_field);
    }
  }
 
  void
  get_bits(const RV& regions, size_t level, const std::string& group) {
    //  Invalid call - return
    if (regions.empty()) return;
 
    if (regions.size() == 1) {
      /*
         There is only one region (ie one range)
         therefore the bitsets are unambiguous
         The bit width of each field implementation is
         simply the bit width of the corresponding field.
       */
      IdDictRegion* region = regions[0];
      for (size_t k = level; k < region->m_implementation.size(); ++k) {
        IdDictFieldImplementation& f = region->m_implementation[k];
        f.set_ored_field(f.field());
      }
      return;
    }
 
    size_t k;
    // Copy the regions provided in the arguments to a local clone.
    RV mr = regions;
    // Compute the number of bits needed at this level
    compute_bits(mr, level, group);
    RV overlapping;
    RV orig;
    RV temp;
    overlapping.reserve(mr.size());
    orig.reserve(mr.size());
    temp.reserve(mr.size());
    for (;; ) {
      if (mr.empty()) {
        break;
      }
      overlapping.clear();
      temp.clear();
      // Find the first non empty Region within the specified group
      IdDictRegion* reference_region = 0;
      for (k = 0; k < mr.size(); ++k) {
        reference_region = mr[k];
        if (reference_region->m_implementation.size() > level) {
          if (group == reference_region->m_group) {
            overlapping.push_back(reference_region);
            break;
          } else {
            temp.push_back(reference_region);
          }
        }
      }
      // Should be redundant with the mr.size() test above, but put here
      // to try to avoid coverity warnings that reference_region may be null.
      if (reference_region == 0) break;
      if (overlapping.empty()) {
        break;
      }
      // Now really split mr into the two subsets
      ++k;
      const IdDictFieldImplementation& f1 = reference_region->implementation(level);
      Range::field ored_field = f1.field();
      // copy into original test sample, some may have already been
      // added to temp above.
      for (; k < mr.size(); ++k) {
        IdDictRegion* region = mr[k];
        temp.push_back(region);
      }
      bool found_overlap = false;
      // Compare the reference field at this level to those in the
      // remaining regions and check for overlap.
      //
      // The comparison must be done repeatedly because the overlap
      // field gets larger and may overlap with previously checked
      // field of a region.
      //
      // By "definition" we require regions in the same group to
      // overlap to have a uniform bit-allocation for a group.
      //
      // For regions outside the current group, the overlap is
      // allowed for the top level fields with the same names. As
      // soon as one finds a field with a different name which is in
      // a region outside the group, this and subsequent fields are
      // ignored.
      //
      do {
        // copy temp into orig, set overlap to false for this loop over regions
        orig.clear();
        orig = temp;
        temp.clear();
        found_overlap = false;
        for (size_t i = 0; i < orig.size(); ++i) {
          IdDictRegion* region = orig[i];
          if (region->m_implementation.size() <= level) continue;
          bool overlap = false;
          const IdDictFieldImplementation& f = region->implementation(level);
          const Range::field& thisField = f.field();
          // Now expand bits by or'ing them with other regions
          // at this level, requiring the name to be the same.
          if (f1.range()->field_name() == f.range()->field_name()) overlap = ored_field.overlaps_with(thisField);
          // Check for either an overlap or force overlap for
          // regions in the same group
          if (overlap || (region->m_group == group)) {
            overlapping.push_back(region);
            ored_field |= thisField;
            found_overlap = true;
          } else {
            temp.push_back(region);
          }
        }
      } while (found_overlap);
 
      // Check overlapping collection - if there are only regions from
      // the same group, we can safely throw away "temp" the other
      // collection
      bool all_within_group = true;
      bool none_within_group = true;
      for (size_t i = 0; i < overlapping.size(); ++i) {
        IdDictRegion* region = overlapping[i];
        if (group == region->m_group) {
          none_within_group = false;
        } else {
          all_within_group = false;
        }
      }
      // Remove temp is no longer needed
      if (all_within_group) temp.clear();
      // Recurse on the remaining fields of the overlapping regions
      //
      // Continue only if there are regions still within the current
      // group
      if (!none_within_group) {
        get_bits(overlapping, level + 1, group);
      }
      // Continue for the other not-yet-overlapping regions.
      mr = temp;
    }
  }
}