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Faster decodeHexNibble (#9896) 

Motivation:

decodeHexNibble can be a lot faster using a lookup table

Modifications:

decodeHexNibble is made faster by using a lookup table

Result:

decodeHexNibble is faster
This commit is contained in:
Francesco Nigro 2019-12-23 21:15:56 +01:00 committed by Norman Maurer
parent 019cdca40b
commit 1e4f0e6a09
2 changed files with 168 additions and 10 deletions
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42
common/src/main/java/io/netty/util/internal/StringUtil.java
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@ -17,6 +17,7 @@ package io.netty.util.internal;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
import java.util.Objects;
@ -40,6 +41,7 @@ public final class StringUtil {
private static final String[] BYTE2HEX_PAD = new String[256];
private static final String[] BYTE2HEX_NOPAD = new String[256];
private static final byte[] HEX2B;
/**
* 2 - Quote character at beginning and end.
@ -55,6 +57,33 @@ public final class StringUtil {
BYTE2HEX_PAD[i] = i > 0xf ? str : ('0' + str);
BYTE2HEX_NOPAD[i] = str;
}
// Generate the lookup table that converts an hex char into its decimal value:
// the size of the table is such that the JVM is capable of save any bounds-check
// if a char type is used as an index.
HEX2B = new byte[Character.MAX_VALUE + 1];
Arrays.fill(HEX2B, (byte) -1);
HEX2B['0'] = (byte) 0;
HEX2B['1'] = (byte) 1;
HEX2B['2'] = (byte) 2;
HEX2B['3'] = (byte) 3;
HEX2B['4'] = (byte) 4;
HEX2B['5'] = (byte) 5;
HEX2B['6'] = (byte) 6;
HEX2B['7'] = (byte) 7;
HEX2B['8'] = (byte) 8;
HEX2B['9'] = (byte) 9;
HEX2B['A'] = (byte) 10;
HEX2B['B'] = (byte) 11;
HEX2B['C'] = (byte) 12;
HEX2B['D'] = (byte) 13;
HEX2B['E'] = (byte) 14;
HEX2B['F'] = (byte) 15;
HEX2B['a'] = (byte) 10;
HEX2B['b'] = (byte) 11;
HEX2B['c'] = (byte) 12;
HEX2B['d'] = (byte) 13;
HEX2B['e'] = (byte) 14;
HEX2B['f'] = (byte) 15;
}
private StringUtil() {
@ -212,18 +241,11 @@ public final class StringUtil {
* given, or {@code -1} if the character is invalid.
*/
public static int decodeHexNibble(final char c) {
assert HEX2B.length == (Character.MAX_VALUE + 1);
// Character.digit() is not used here, as it addresses a larger
// set of characters (both ASCII and full-width latin letters).
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;
final int index = c;
return HEX2B[index];
}
/**

136
microbench/src/main/java/io/netty/handler/codec/http/DecodeHexBenchmark.java Normal file
View File

@ -0,0 +1,136 @@
/*
* 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:
*
* 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 io.netty.handler.codec.http;
import io.netty.microbench.util.AbstractMicrobenchmark;
import io.netty.util.internal.PlatformDependent;
import io.netty.util.internal.StringUtil;
import org.openjdk.jmh.annotations.Benchmark;
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.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;
private char[] hexDigits;
@Setup
public void init() {
hexDigits = hex.toCharArray();
}
@Benchmark
public long hexDigits() {
long v = 0;
final char[] hexDigits = this.hexDigits;
for (int i = 0, size = hexDigits.length; i < size; i++) {
v += StringUtil.decodeHexNibble(hexDigits[i]);
}
return v;
}
@Benchmark
public long hexDigitsWithChecks() {
long v = 0;
final char[] hexDigits = this.hexDigits;
for (int i = 0, size = hexDigits.length; i < size; i++) {
v += decodeHexNibbleWithCheck(hexDigits[i]);
}
return v;
}
@Benchmark
public long hexDigitsOriginal() {
long v = 0;
final char[] hexDigits = this.hexDigits;
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'] = (byte) 0;
HEX2B['1'] = (byte) 1;
HEX2B['2'] = (byte) 2;
HEX2B['3'] = (byte) 3;
HEX2B['4'] = (byte) 4;
HEX2B['5'] = (byte) 5;
HEX2B['6'] = (byte) 6;
HEX2B['7'] = (byte) 7;
HEX2B['8'] = (byte) 8;
HEX2B['9'] = (byte) 9;
HEX2B['A'] = (byte) 10;
HEX2B['B'] = (byte) 11;
HEX2B['C'] = (byte) 12;
HEX2B['D'] = (byte) 13;
HEX2B['E'] = (byte) 14;
HEX2B['F'] = (byte) 15;
HEX2B['a'] = (byte) 10;
HEX2B['b'] = (byte) 11;
HEX2B['c'] = (byte) 12;
HEX2B['d'] = (byte) 13;
HEX2B['e'] = (byte) 14;
HEX2B['f'] = (byte) 15;
}
private static int decodeHexNibbleWithCheck(final char c) {
final int index = c;
if (index >= HEX2B.length) {
return -1;
}
if (PlatformDependent.hasUnsafe()) {
return PlatformDependent.getByte(HEX2B, index);
}
return HEX2B[index];
}
}