Merge "Copy StringPool to framework" am: ffe7986d71

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1684883

Change-Id: Idb0558e5304dfa0ca8446efd43c4c04b83bf6a7c

core/java/android/util/JsonReader.java

@@ -16,7 +16,7 @@
 
 package android.util;
 
-import libcore.internal.StringPool;
+import com.android.internal.util.StringPool;
 
 import java.io.Closeable;
 import java.io.EOFException;

core/java/com/android/internal/util/StringPool.java

@@ -0,0 +1,77 @@
+/*
+ * Copyright (C) 2010 The Android Open Source Project
+ *
+ * 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 com.android.internal.util;
+
+/**
+ * A pool of string instances. Unlike the {@link String#intern() VM's
+ * interned strings}, this pool provides no guarantee of reference equality.
+ * It is intended only to save allocations. This class is not thread safe.
+ *
+ * @hide
+ */
+public final class StringPool {
+
+    private final String[] mPool = new String[512];
+
+    /**
+     * Constructs string pool.
+     */
+    public StringPool() {
+    }
+
+    private static boolean contentEquals(String s, char[] chars, int start, int length) {
+        if (s.length() != length) {
+            return false;
+        }
+        for (int i = 0; i < length; i++) {
+            if (chars[start + i] != s.charAt(i)) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    /**
+     * Returns a string equal to {@code new String(array, start, length)}.
+     *
+     * @param array  buffer containing string chars
+     * @param start  offset in {@code array} where string starts
+     * @param length length of string
+     * @return string equal to {@code new String(array, start, length)}
+     */
+    public String get(char[] array, int start, int length) {
+        // Compute an arbitrary hash of the content
+        int hashCode = 0;
+        for (int i = start; i < start + length; i++) {
+            hashCode = (hashCode * 31) + array[i];
+        }
+
+        // Pick a bucket using Doug Lea's supplemental secondaryHash function (from HashMap)
+        hashCode ^= (hashCode >>> 20) ^ (hashCode >>> 12);
+        hashCode ^= (hashCode >>> 7) ^ (hashCode >>> 4);
+        int index = hashCode & (mPool.length - 1);
+
+        String pooled = mPool[index];
+        if (pooled != null && contentEquals(pooled, array, start, length)) {
+            return pooled;
+        }
+
+        String result = new String(array, start, length);
+        mPool[index] = result;
+        return result;
+    }
+}

core/tests/utiltests/src/com/android/internal/util/StringPoolTest.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) 2010 The Android Open Source Project
+ *
+ * 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 com.android.internal.util;
+
+import android.test.AndroidTestCase;
+import android.test.suitebuilder.annotation.SmallTest;
+
+@SmallTest
+public final class StringPoolTest extends AndroidTestCase {
+
+    public void testStringPool() {
+        StringPool stringPool = new StringPool();
+        String bcd = stringPool.get(new char[] { 'a', 'b', 'c', 'd', 'e' }, 1, 3);
+        assertEquals("bcd", bcd);
+        assertSame(bcd, stringPool.get(new char[] { 'a', 'b', 'c', 'd', 'e' }, 1, 3));
+    }
+
+    public void testHashCollision() {
+        StringPool stringPool = new StringPool();
+        char[] a = { (char) 1, (char) 0 };
+        char[] b = { (char) 0, (char) 31 };
+        assertEquals(new String(a).hashCode(), new String(b).hashCode());
+
+        String aString = stringPool.get(a, 0, 2);
+        assertEquals(new String(a), aString);
+        String bString = stringPool.get(b, 0, 2);
+        assertEquals(new String(b), bString);
+        assertSame(bString, stringPool.get(b, 0, 2));
+        assertNotSame(aString, stringPool.get(a, 0, 2));
+    }
+}