From fc3d92f58dd6a0c22dcbbf99829a92c7b164b5de Mon Sep 17 00:00:00 2001
From: Alexey Andreev <konsoletyper@gmail.com>
Date: Sat, 30 Sep 2023 07:17:22 +0200
Subject: [PATCH] classlib: improve performance of String.toLower/toUpper

---
 .../classlib/impl/unicode/CharMapping.java    | 26 +++++++++
 .../classlib/impl/unicode/UnicodeHelper.java  | 20 +++++++
 .../teavm/classlib/java/lang/TCharacter.java  | 35 +++++++-----
 .../org/teavm/classlib/java/lang/TString.java | 54 +++++++++++++++++++
 4 files changed, 122 insertions(+), 13 deletions(-)
 create mode 100644 classlib/src/main/java/org/teavm/classlib/impl/unicode/CharMapping.java

diff --git a/classlib/src/main/java/org/teavm/classlib/impl/unicode/CharMapping.java b/classlib/src/main/java/org/teavm/classlib/impl/unicode/CharMapping.java
new file mode 100644
index 000000000..e620255b5
--- /dev/null
+++ b/classlib/src/main/java/org/teavm/classlib/impl/unicode/CharMapping.java
@@ -0,0 +1,26 @@
+/*
+ *  Copyright 2023 Alexey Andreev.
+ *
+ *  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 org.teavm.classlib.impl.unicode;
+
+public class CharMapping {
+    public final int[] binarySearchTable;
+    public final int[] fastTable;
+
+    public CharMapping(int[] binarySearchTable, int[] fastTable) {
+        this.binarySearchTable = binarySearchTable;
+        this.fastTable = fastTable;
+    }
+}
diff --git a/classlib/src/main/java/org/teavm/classlib/impl/unicode/UnicodeHelper.java b/classlib/src/main/java/org/teavm/classlib/impl/unicode/UnicodeHelper.java
index 1a0047940..4ef63a720 100644
--- a/classlib/src/main/java/org/teavm/classlib/impl/unicode/UnicodeHelper.java
+++ b/classlib/src/main/java/org/teavm/classlib/impl/unicode/UnicodeHelper.java
@@ -126,6 +126,26 @@ public final class UnicodeHelper {
         return data;
     }
 
+    public static CharMapping createCharMapping(int[] data) {
+        var result = new int[65536];
+        var last = 0;
+        var lastValue = 0;
+        for (var i = 0; i < data.length; i += 2) {
+            var key = data[i];
+            var value = data[i + 1];
+            if (key >= result.length) {
+                if (key == last) {
+                    break;
+                }
+                key = result.length;
+            }
+            Arrays.fill(result, last, key, lastValue);
+            last = key;
+            lastValue = value;
+        }
+        return new CharMapping(data, result);
+    }
+
     public static char encodeByte(byte b) {
         if (b < '\"' - ' ') {
             return (char) (b + ' ');
diff --git a/classlib/src/main/java/org/teavm/classlib/java/lang/TCharacter.java b/classlib/src/main/java/org/teavm/classlib/java/lang/TCharacter.java
index 6df537812..b96d20191 100644
--- a/classlib/src/main/java/org/teavm/classlib/java/lang/TCharacter.java
+++ b/classlib/src/main/java/org/teavm/classlib/java/lang/TCharacter.java
@@ -15,6 +15,7 @@
  */
 package org.teavm.classlib.java.lang;
 
+import org.teavm.classlib.impl.unicode.CharMapping;
 import org.teavm.classlib.impl.unicode.UnicodeHelper;
 import org.teavm.platform.metadata.StringResource;
 
@@ -87,9 +88,9 @@ public class TCharacter extends TObject implements TComparable<TCharacter> {
     public static final int BYTES = SIZE / Byte.SIZE;
     static final int ERROR = 0xFFFFFFFF;
     private static int[] digitMapping;
-    private static int[] titleCaseMapping;
-    private static int[] upperCaseMapping;
-    private static int[] lowerCaseMapping;
+    private static CharMapping titleCaseMapping;
+    private static CharMapping upperCaseMapping;
+    private static CharMapping lowerCaseMapping;
     private static UnicodeHelper.Range[] classMapping;
     private final char value;
     private static TCharacter[] characterCache = new TCharacter[128];
@@ -241,9 +242,10 @@ public class TCharacter extends TObject implements TComparable<TCharacter> {
         return mapChar(getLowerCaseMapping(), ch);
     }
 
-    private static int[] getLowerCaseMapping() {
+    private static CharMapping getLowerCaseMapping() {
         if (lowerCaseMapping == null) {
-            lowerCaseMapping = UnicodeHelper.decodeCaseMapping(acquireLowerCaseMapping().getValue());
+            lowerCaseMapping = UnicodeHelper.createCharMapping(
+                    UnicodeHelper.decodeCaseMapping(acquireLowerCaseMapping().getValue()));
         }
         return lowerCaseMapping;
     }
@@ -259,9 +261,10 @@ public class TCharacter extends TObject implements TComparable<TCharacter> {
         return mapChar(getUpperCaseMapping(), codePoint);
     }
 
-    private static int[] getUpperCaseMapping() {
+    private static CharMapping getUpperCaseMapping() {
         if (upperCaseMapping == null) {
-            upperCaseMapping = UnicodeHelper.decodeCaseMapping(acquireUpperCaseMapping().getValue());
+            upperCaseMapping = UnicodeHelper.createCharMapping(
+                    UnicodeHelper.decodeCaseMapping(acquireUpperCaseMapping().getValue()));
         }
         return upperCaseMapping;
     }
@@ -280,21 +283,27 @@ public class TCharacter extends TObject implements TComparable<TCharacter> {
         return (char) toTitleCase((int) c);
     }
 
-    private static int[] getTitleCaseMapping() {
+    private static CharMapping getTitleCaseMapping() {
         if (titleCaseMapping == null) {
-            titleCaseMapping = UnicodeHelper.decodeCaseMapping(acquireTitleCaseMapping().getValue());
+            titleCaseMapping = UnicodeHelper.createCharMapping(
+                    UnicodeHelper.decodeCaseMapping(acquireTitleCaseMapping().getValue()));
         }
         return titleCaseMapping;
     }
 
     private static native StringResource acquireTitleCaseMapping();
 
-    private static int mapChar(int[] table, int codePoint) {
-        int index = binarySearchTable(table, codePoint);
-        if (index < 0 || index >= table.length / 2) {
+    private static int mapChar(CharMapping table, int codePoint) {
+        if (codePoint < table.fastTable.length) {
+            return codePoint + table.fastTable[codePoint];
+        }
+
+        var binSearchTable = table.binarySearchTable;
+        int index = binarySearchTable(binSearchTable, codePoint);
+        if (index < 0 || index * 2 >= binSearchTable.length) {
             return 0;
         }
-        return codePoint + table[index * 2 + 1];
+        return codePoint + binSearchTable[index * 2 + 1];
     }
 
     private static int binarySearchTable(int[] data, int key) {
diff --git a/classlib/src/main/java/org/teavm/classlib/java/lang/TString.java b/classlib/src/main/java/org/teavm/classlib/java/lang/TString.java
index 272145bf2..69ae16c20 100644
--- a/classlib/src/main/java/org/teavm/classlib/java/lang/TString.java
+++ b/classlib/src/main/java/org/teavm/classlib/java/lang/TString.java
@@ -640,6 +640,33 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         if (isEmpty()) {
             return this;
         }
+
+        var hasCharsToTransform = false;
+        var hasSurrogates = false;
+        for (var c : characters) {
+            if (Character.toLowerCase(c) != c) {
+                hasCharsToTransform = true;
+                break;
+            }
+            if (Character.isSurrogate(c)) {
+                hasSurrogates = true;
+            }
+        }
+        if (!hasCharsToTransform) {
+            return this;
+        }
+        return hasSurrogates ? toLowerCaseCodePoints() : toLowerCaseChars();
+    }
+
+    private TString toLowerCaseChars() {
+        var chars = new char[characters.length];
+        for (int i = 0; i < characters.length; ++i) {
+            chars[i] = TCharacter.toLowerCase(characters[i]);
+        }
+        return new TString(chars);
+    }
+
+    private TString toLowerCaseCodePoints() {
         int[] codePoints = new int[characters.length];
         int codePointCount = 0;
         for (int i = 0; i < characters.length; ++i) {
@@ -663,6 +690,33 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         if (isEmpty()) {
             return this;
         }
+
+        var hasCharsToTransform = false;
+        var hasSurrogates = false;
+        for (var c : characters) {
+            if (Character.toUpperCase(c) != c) {
+                hasCharsToTransform = true;
+                break;
+            }
+            if (Character.isSurrogate(c)) {
+                hasSurrogates = true;
+            }
+        }
+        if (!hasCharsToTransform) {
+            return this;
+        }
+        return hasSurrogates ? toUpperCaseCodePoints() : toUpperCaseChars();
+    }
+
+    private TString toUpperCaseChars() {
+        var chars = new char[characters.length];
+        for (int i = 0; i < characters.length; ++i) {
+            chars[i] = TCharacter.toUpperCase(characters[i]);
+        }
+        return new TString(chars);
+    }
+
+    private TString toUpperCaseCodePoints() {
         int[] codePoints = new int[characters.length];
         int codePointCount = 0;
         for (int i = 0; i < characters.length; ++i) {