tables_contained_in.h

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/*
   Copyright (c) 2019, 2023, Oracle and/or its affiliates.
 
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   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.
 
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   You should have received a copy of the GNU General Public License
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   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
 
#ifndef TABLES_CONTAINED_IN_H_
#define TABLES_CONTAINED_IN_H_
 
#include <string.h>
 
#include "my_inttypes.h"
#include "sql/sql_optimizer.h"
 
#ifdef _MSC_VER
#include <intrin.h>
#pragma intrinsic(_BitScanForward64)
#endif
 
// A utility class to loop over all set bits in the given map.
// Use as:
//
//   qep_tab_map = ...;
//   for (QEP_TAB *qep_tab : TablesContainedIn(join, qep_tab_map)) {
//      ...
//   }
class TablesContainedIn {
 public:
  class iterator {
   private:
    const JOIN *const m_join;
    qep_tab_map m_bits_left;
 
   public:
    iterator(const JOIN *join, qep_tab_map map)
        : m_join(join), m_bits_left(map) {}
    bool operator==(const iterator &other) const {
      assert(m_join == other.m_join);
      return m_bits_left == other.m_bits_left;
    }
    bool operator!=(const iterator &other) const {
      assert(m_join == other.m_join);
      return m_bits_left != other.m_bits_left;
    }
    QEP_TAB *operator*() const {
      // Find the QEP_TAB that corresponds to the lowest set bit.
      assert(m_bits_left != 0);
#ifdef _MSC_VER
      unsigned long idx;
      _BitScanForward64(&idx, m_bits_left);
#else
      size_t idx = ffsll(m_bits_left) - 1;
#endif
      assert(idx < m_join->tables);
      return &m_join->qep_tab[idx];
    }
    iterator &operator++() {
      // Clear the lowest set bit.
      assert(m_bits_left != 0);
      m_bits_left &= (m_bits_left - 1);
      return *this;
    }
  };
 
  TablesContainedIn(const JOIN *join, qep_tab_map map)
      : m_join(join), m_initial_map(map) {}
 
  iterator begin() const { return {m_join, m_initial_map}; }
  iterator end() const { return {m_join, 0}; }
 
 private:
  const JOIN *const m_join;
  const qep_tab_map m_initial_map;
};
 
#endif  // TABLES_CONTAINED_IN_H_