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// ordering.h
/* Copyright 2009 10gen Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#pragma once
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 string() const {
StringBuilder buf(32);
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);
}
};
}
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