/*
* 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.
*/
package com.facebook.presto.operator.exchange;
import com.facebook.presto.operator.HashGenerator;
import com.facebook.presto.spi.Page;
import io.airlift.slice.XxHash64;
import static com.google.common.base.Preconditions.checkArgument;
public class LocalPartitionGenerator
{
private final HashGenerator hashGenerator;
private final int hashMask;
public LocalPartitionGenerator(HashGenerator hashGenerator, int partitionCount)
{
this.hashGenerator = hashGenerator;
checkArgument(Integer.bitCount(partitionCount) == 1, "partitionCount must be a power of 2");
hashMask = partitionCount - 1;
}
public int getPartition(int position, Page page)
{
long rawHash = getRawHash(position, page);
return processRawHash(rawHash) & hashMask;
}
public long getRawHash(int position, Page page)
{
return hashGenerator.hashPosition(position, page);
}
public int getPartition(long rawHash)
{
return processRawHash(rawHash) & hashMask;
}
private static int processRawHash(long rawHash)
{
// mix the bits so we don't use the same hash used to distribute between stages
return (int) XxHash64.hash(Long.reverse(rawHash));
}
}