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// ordering.h
/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* 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
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* 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 Server Side 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:
static constexpr size_t kMaxCompoundIndexKeys = size_t{32};
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 < kMaxCompoundIndexKeys);
if (e.number() < 0)
b |= (1 << n);
n++;
}
return Ordering(b);
}
};
}
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