org.apache.flink.table.planner.codegen.HashCodeGenerator.scala Maven / Gradle / Ivy

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This module bridges Table/SQL API and runtime. It contains all resources that are required during pre-flight and runtime phase. The content of this module is work-in-progress. It will replace flink-table-planner once it is stable. See FLINK-11439 and FLIP-32 for more details.

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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.flink.table.planner.codegen

import org.apache.flink.table.planner.codegen.CodeGenUtils.{ROW_DATA, hashCodeForType, newName}
import org.apache.flink.table.planner.codegen.Indenter.toISC
import org.apache.flink.table.runtime.generated.{GeneratedHashFunction, HashFunction}
import org.apache.flink.table.types.logical.LogicalType
import org.apache.flink.util.MathUtils

/**
  * CodeGenerator for hash code RowData, Calculate a hash value based on some fields
  * of RowData.
  * NOTE: If you need a hash value that is more evenly distributed, call [[MathUtils.murmurHash]]
  * outside to scatter.
  */
object HashCodeGenerator {

  /**
    * A sequence of prime numbers to be used for salting the computed hash values.
    * Based on some empirical evidence, we are using a 32-element subsequence of the
    * OEIS sequence #A068652 (numbers such that every cyclic permutation is a prime).
    *
    * @see 
    *        http://en.wikipedia.org/wiki/List_of_prime_numbers
    * @see http://oeis.org/A068652
    */
  val HASH_SALT: Array[Int] = Array[Int](
    73, 79, 97, 113, 131, 197, 199, 311, 337, 373, 719, 733, 919, 971, 991, 1193, 1931, 3119,
    3779, 7793, 7937, 9311, 9377, 11939, 19391, 19937, 37199, 39119, 71993, 91193, 93719, 93911)

  def generateRowHash(
      ctx: CodeGeneratorContext,
      input: LogicalType,
      name: String,
      hashFields: Array[Int]): GeneratedHashFunction = {
    val className = newName(name)
    val baseClass = classOf[HashFunction]
    val inputTerm = CodeGenUtils.DEFAULT_INPUT1_TERM

    val accessExprs = hashFields.map(
      idx => GenerateUtils.generateFieldAccess(ctx, input, inputTerm, idx))

    val (hashBody, resultTerm) = generateCodeBody(ctx, accessExprs)
    val code =
      j"""
      public class $className implements ${baseClass.getCanonicalName} {

        ${ctx.reuseMemberCode()}

        public $className(Object[] references) throws Exception {
          ${ctx.reuseInitCode()}
        }

        @Override
        public int hashCode($ROW_DATA $inputTerm) {
          ${ctx.reuseLocalVariableCode()}
          $hashBody
          return $resultTerm;
        }

        ${ctx.reuseInnerClassDefinitionCode()}
      }
    """.stripMargin

    new GeneratedHashFunction(className, code, ctx.references.toArray)
  }

  private def generateCodeBody(
      ctx: CodeGeneratorContext,
      accessExprs: Seq[GeneratedExpression]): (String, String) = {
    val hashIntTerm = CodeGenUtils.newName("hashCode")
    var i = -1
    val hashBodyCode = accessExprs.map(expr => {
      i = i + 1
      s"""
         |$hashIntTerm *= ${HASH_SALT(i & 0x1F)};
         |${expr.code}
         |if (!${expr.nullTerm}) {
         | $hashIntTerm += ${hashCodeForType(ctx, expr.resultType, expr.resultTerm)};
         |}
         |""".stripMargin

    }).mkString("\n")
    (s"""
        |int $hashIntTerm = 0;
        |$hashBodyCode""".stripMargin, hashIntTerm)
  }
}