1 files changed, 73 insertions, 0 deletions
diff --git a/src/mongo/bson/ordering.h b/src/mongo/bson/ordering.h
new file mode 100644
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+++ b/src/mongo/bson/ordering.h
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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 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);
+        }
+    };
+
+}