text: // ordering.h
  
  /*    Copyright 2009 10gen Inc.
   *
   *    This program is free software: you can redistribute it and/or  modify
   *    it under the terms of the GNU Affero General Public License, version 3,
   *    as published by the Free Software Foundation.
   *
   *    This program is distributed in the hope that it will be useful,
   *    but WITHOUT ANY WARRANTY; without even the implied warranty of
   *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   *    GNU Affero General Public License for more details.
   *
   *    You should have received a copy of the GNU Affero General Public License
   *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
   *
   *    As a special exception, the copyright holders give permission to link the
   *    code of portions of this program with the OpenSSL library under certain
   *    conditions as described in each individual source file and distribute
   *    linked combinations including the program with the OpenSSL library. You
   *    must comply with the GNU Affero General Public License in all respects
   *    for all of the code used other than as permitted herein. If you modify
   *    file(s) with this exception, you may extend this exception to your
   *    version of the file(s), but you are not obligated to do so. If you do not
   *    wish to do so, delete this exception statement from your version. If you
   *    delete this exception statement from all source files in the program,
   *    then also delete it in the license file.
   */
  
  #pragma once
  
  #include "mongo/bson/bsonobj.h"
  
  namespace mongo {
  
  // todo: ideally move to db/ instead of bson/, but elim any dependencies first
  
  /** A precomputation of a BSON index or sort key pattern.  That is something like:
         { a : 1, b : -1 }
      The constructor is private to make conversion more explicit so we notice where we call make().
      Over time we should push this up higher and higher.
  */
  class Ordering {
      unsigned bits;
      Ordering(unsigned b) : bits(b) {}
  
  public:
      Ordering(const Ordering& r) : bits(r.bits) {}
      void operator=(const Ordering& r) {
          bits = r.bits;
      }
  
      /** so, for key pattern { a : 1, b : -1 }
          get(0) == 1
          get(1) == -1
      */
      int get(int i) const {
          return ((1 << i) & bits) ? -1 : 1;
      }
  
      // for woCompare...
      unsigned descending(unsigned mask) const {
          return bits & mask;
      }
  
      /*operator std::string() const {
          StringBuilder buf;
          for ( unsigned i=0; i<nkeys; i++)
              buf.append( get(i) > 0 ? "+" : "-" );
          return buf.str();
      }*/
  
      static Ordering make(const BSONObj& obj) {
          unsigned b = 0;
          BSONObjIterator k(obj);
          unsigned n = 0;
          while (1) {
              BSONElement e = k.next();
              if (e.eoo())
                  break;
              uassert(13103, "too many compound keys", n <= 31);
              if (e.number() < 0)
                  b |= (1 << n);
              n++;
          }
          return Ordering(b);
      }
  };
  }
  