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   /*
    * Copyright 2019 The Netty Project
    *
    * The Netty Project 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:
    *
    *   https://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 io.netty.handler.codec.http;
  
  import io.netty.microbench.util.AbstractMicrobenchmark;
  import io.netty.util.internal.MathUtil;
  import io.netty.util.internal.PlatformDependent;
  import io.netty.util.internal.StringUtil;
  import org.openjdk.jmh.annotations.Benchmark;
  import org.openjdk.jmh.annotations.CompilerControl;
  import org.openjdk.jmh.annotations.CompilerControl.Mode;
  import org.openjdk.jmh.annotations.Measurement;
  import org.openjdk.jmh.annotations.OutputTimeUnit;
  import org.openjdk.jmh.annotations.Param;
  import org.openjdk.jmh.annotations.Scope;
  import org.openjdk.jmh.annotations.Setup;
  import org.openjdk.jmh.annotations.State;
  import org.openjdk.jmh.annotations.Warmup;
  
  import java.util.Arrays;
  import java.util.Random;
  import java.util.concurrent.TimeUnit;
  
  @State(Scope.Benchmark)
  @Warmup(iterations = 5, time = 1)
  @Measurement(iterations = 5, time = 1)
  @OutputTimeUnit(TimeUnit.MICROSECONDS)
  public class DecodeHexBenchmark extends AbstractMicrobenchmark {
  
      @Param({
              //with HEX chars
              "135aBa9BBCEA030b947d79fCcaf48Bde",
              //with HEX chars + 'g'
              "4DDeA5gDD1C6fE567E1b6gf0C40FEcDg",
      })
      private String hex;
      // Needs to specify a high number of inputs to allow the current strategy
      // on nextHexDigits to produce enough branch-misses
      @Param({ "2048" })
      private int inputs;
      private char[][] hexDigits;
      private static final long SEED = 1578675524L;
      private long next;
  
      @Setup
      public void init() {
          final char[] hexCh = hex.toCharArray();
          next = 0;
          inputs = MathUtil.findNextPositivePowerOfTwo(inputs);
          hexDigits = new char[inputs][];
          hexDigits[0] = hexCh;
          if (inputs > 1) {
              final Random rnd = new Random(SEED);
              for (int i = 1; i < inputs; i++) {
                  hexDigits[i] = shuffle(Arrays.copyOf(hexCh, hexCh.length), rnd);
              }
          }
      }
  
      // https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle
      private static char[] shuffle(char[] chars, Random rnd) {
          int index;
          char tmp;
          for (int i = chars.length - 1; i > 0; i--) {
              index = rnd.nextInt(i + 1);
              tmp = chars[index];
              chars[index] = chars[i];
              chars[i] = tmp;
          }
          return chars;
      }
  
      private int nextHexDigits() {
          final int idx = (int) (next & (inputs - 1));
          next++;
          return idx;
      }
  
      @Benchmark
      @CompilerControl(Mode.DONT_INLINE)
      public long hexDigits() {
          long v = 0;
          final char[] hexDigits = this.hexDigits[nextHexDigits()];
          for (int i = 0, size = hexDigits.length; i < size; i++) {
              v += StringUtil.decodeHexNibble(hexDigits[i]);
          }
         return v;
     }
 
     @Benchmark
     @CompilerControl(Mode.DONT_INLINE)
     public long hexDigitsWithChecks() {
         long v = 0;
         final char[] hexDigits = this.hexDigits[nextHexDigits()];
         for (int i = 0, size = hexDigits.length; i < size; i++) {
             v += decodeHexNibbleWithCheck(hexDigits[i]);
         }
         return v;
     }
 
     @Benchmark
     @CompilerControl(Mode.DONT_INLINE)
     public long hexDigitsOriginal() {
         long v = 0;
         final char[] hexDigits = this.hexDigits[nextHexDigits()];
         for (int i = 0, size = hexDigits.length; i < size; i++) {
             v += decodeHexNibble(hexDigits[i]);
         }
         return v;
     }
 
     private static int decodeHexNibble(final char c) {
         if (c >= '0' && c <= '9') {
             return c - '0';
         }
         if (c >= 'A' && c <= 'F') {
             return c - ('A' - 0xA);
         }
         if (c >= 'a' && c <= 'f') {
             return c - ('a' - 0xA);
         }
         return -1;
     }
 
     private static final byte[] HEX2B;
 
     static {
         HEX2B = new byte['f' + 1];
         Arrays.fill(HEX2B, (byte) -1);
         HEX2B['0'] = 0;
         HEX2B['1'] = 1;
         HEX2B['2'] = 2;
         HEX2B['3'] = 3;
         HEX2B['4'] = 4;
         HEX2B['5'] = 5;
         HEX2B['6'] = 6;
         HEX2B['7'] = 7;
         HEX2B['8'] = 8;
         HEX2B['9'] = 9;
         HEX2B['A'] = 10;
         HEX2B['B'] = 11;
         HEX2B['C'] = 12;
         HEX2B['D'] = 13;
         HEX2B['E'] = 14;
         HEX2B['F'] = 15;
         HEX2B['a'] = 10;
         HEX2B['b'] = 11;
         HEX2B['c'] = 12;
         HEX2B['d'] = 13;
         HEX2B['e'] = 14;
         HEX2B['f'] = 15;
     }
 
     private static int decodeHexNibbleWithCheck(final char c) {
         if (c >= HEX2B.length) {
             return -1;
         }
         if (PlatformDependent.hasUnsafe()) {
             return PlatformDependent.getByte(HEX2B, c);
         }
         return HEX2B[c];
     }
 
 }