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8240094: Optimize empty substring handling

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Reviewed-by: redestad, igerasim, jlaskey
This commit is contained in:
Sergei Tsypanov 2020-02-26 21:24:02 +01:00 • committed by Claes Redestad
parent 257de28b2c
commit f729514ebd
4 changed files with 23 additions and 18 deletions
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6
src/java.base/share/classes/java/lang/String.java
View file

@ -1,5 +1,5 @@
/*
* Copyright (c) 1994, 2019, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 1994, 2020, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -1819,7 +1819,7 @@ public final class String
* @param src the characters being searched.
* @param srcCoder coder handles the mapping between bytes/chars
* @param srcCount count of the source string.
* @param tgt the characters being searched for.
* @param tgtStr the characters being searched for.
* @param fromIndex the index to begin searching from.
*/
static int lastIndexOf(byte[] src, byte srcCoder, int srcCount,
@ -1900,10 +1900,10 @@ public final class String
public String substring(int beginIndex, int endIndex) {
int length = length();
checkBoundsBeginEnd(beginIndex, endIndex, length);
int subLen = endIndex - beginIndex;
if (beginIndex == 0 && endIndex == length) {
return this;
}
int subLen = endIndex - beginIndex;
return isLatin1() ? StringLatin1.newString(value, beginIndex, subLen)
: StringUTF16.newString(value, beginIndex, subLen);
}

11
src/java.base/share/classes/java/lang/StringLatin1.java
View file

@ -1,5 +1,5 @@
/*
* Copyright (c) 2015, 2019, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2015, 2020, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -630,17 +630,11 @@ final class StringLatin1 {
public static String stripLeading(byte[] value) {
int left = indexOfNonWhitespace(value);
if (left == value.length) {
return "";
}
return (left != 0) ? newString(value, left, value.length - left) : null;
}
public static String stripTrailing(byte[] value) {
int right = lastIndexOfNonWhitespace(value);
if (right == 0) {
return "";
}
return (right != value.length) ? newString(value, 0, right) : null;
}
@ -764,6 +758,9 @@ final class StringLatin1 {
}
public static String newString(byte[] val, int index, int len) {
if (len == 0) {
return "";
}
return new String(Arrays.copyOfRange(val, index, index + len),
LATIN1);
}

11
src/java.base/share/classes/java/lang/StringUTF16.java
View file

@ -1,5 +1,5 @@
/*
* Copyright (c) 2015, 2019, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2015, 2020, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -1016,18 +1016,12 @@ final class StringUTF16 {
public static String stripLeading(byte[] value) {
int length = value.length >>> 1;
int left = indexOfNonWhitespace(value);
if (left == length) {
return "";
}
return (left != 0) ? newString(value, left, length - left) : null;
}
public static String stripTrailing(byte[] value) {
int length = value.length >>> 1;
int right = lastIndexOfNonWhitespace(value);
if (right == 0) {
return "";
}
return (right != length) ? newString(value, 0, right) : null;
}
@ -1132,6 +1126,9 @@ final class StringUTF16 {
}
public static String newString(byte[] val, int index, int len) {
if (len == 0) {
return "";
}
if (String.COMPACT_STRINGS) {
byte[] buf = compress(val, index, len);
if (buf != null) {

13
test/micro/org/openjdk/bench/java/lang/StringSubstring.java
View file

@ -1,5 +1,5 @@
/*
* Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2019, 2020, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -28,6 +28,9 @@ import java.util.concurrent.TimeUnit;
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@Fork(value = 3)
@Warmup(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
@Measurement(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
@State(Scope.Benchmark)
public class StringSubstring {
@ -42,4 +45,12 @@ public class StringSubstring {
public String from26toEnd1() {
return s.substring(26, s.length());
}
/**
* An empty substring should not allocate a new String
*/
@Benchmark
public String empty() {
return s.substring(17, 17);
}
}