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   * Copyright (c) 1999, 2021, 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
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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   */
  
  package openjdk.tools.javac.util;
  
  import java.lang.ref.SoftReference;
  
  import openjdk.tools.javac.util.DefinedBy.Api;
  
  /**
   * Implementation of Name.Table that stores all names in a single shared
   * byte array, expanding it as needed. This avoids the overhead incurred
   * by using an array of bytes for each name.
   *
   *  <p><b>This is NOT part of any supported API.
   *  If you write code that depends on this, you do so at your own risk.
   *  This code and its internal interfaces are subject to change or
   *  deletion without notice.</b>
   */
  public class SharedNameTable extends Name.Table {
      // maintain a freelist of recently used name tables for reuse.
      private static List<SoftReference<SharedNameTable>> freelist = List.nil();
  
  
      static public synchronized SharedNameTable create(Names names, Context context) {
  
  
  
          while (freelist.nonEmpty()) {
              SharedNameTable t = freelist.head.get();
              freelist = freelist.tail;
              if (t != null) {
                  return t;
              }
          }
          return new SharedNameTable(names, context);
      }
  
      private static synchronized void dispose(SharedNameTable t) {
          freelist = freelist.prepend(new SoftReference<>(t));
      }
  
      /** The hash table for names.
       */
      private NameImpl[] hashes;
  
      /** The shared byte array holding all encountered names.
       */
      public byte[] bytes;
  
      /** The mask to be used for hashing
       */
      private int hashMask;
  
      /** The number of filled bytes in `names'.
       */
      private int nc = 0;
  
      /** Allocator
       *  @param names The main name table
       *  @param hashSize the (constant) size to be used for the hash table
       *                  needs to be a power of two.
       *  @param nameSize the initial size of the name table.
       */
      public SharedNameTable(Names names, Context context, int hashSize, int nameSize) {
          super(names, context);
          hashMask = hashSize - 1;
          hashes = new NameImpl[hashSize];
          bytes = new byte[nameSize];
  
      }
  
      public SharedNameTable(Names names, Context context) {
          this(names, context, 0x8000, 0x20000);
      }
  
      @Override
      public Name fromChars(char[] cs, int start, int len) {
          int nc = this.nc;
          byte[] bytes = this.bytes = ArrayUtils.ensureCapacity(this.bytes, nc + len * 3);
          int nbytes = Convert.chars2utf(cs, start, bytes, nc, len) - nc;
          int h = hashValue(bytes, nc, nbytes) & hashMask;
          NameImpl n = hashes[h];
          while (n != null &&
                  (n.getByteLength() != nbytes ||
                  !equals(bytes, n.index, bytes, nc, nbytes))) {
              n = n.next;
          }
          if (n == null) {
              n = new NameImpl(this);
              n.index = nc;
              n.length = nbytes;
              n.next = hashes[h];
              hashes[h] = n;
              this.nc = nc + nbytes;
              if (nbytes == 0) {
                  this.nc++;
              }
          }
          return n;
      }
  
      @Override
      public Name fromUtf(byte[] cs, int start, int len) {
          int h = hashValue(cs, start, len) & hashMask;
          NameImpl n = hashes[h];
          byte[] names = this.bytes;
          while (n != null &&
                  (n.getByteLength() != len || !equals(names, n.index, cs, start, len))) {
              n = n.next;
          }
          if (n == null) {
              int nc = this.nc;
              names = this.bytes = ArrayUtils.ensureCapacity(names, nc + len);
              System.arraycopy(cs, start, names, nc, len);
              n = new NameImpl(this);
              n.index = nc;
              n.length = len;
              n.next = hashes[h];
              hashes[h] = n;
              this.nc = nc + len;
              if (len == 0) {
                  this.nc++;
              }
          }
          return n;
      }
  
      @Override
      public void dispose() {
          dispose(this);
      }
  
      static class NameImpl extends Name {
          /** The next name occupying the same hash bucket.
           */
          NameImpl next;
  
          /** The index where the bytes of this name are stored in the global name
           *  buffer `byte'.
           */
          int index;
  
          /** The number of bytes in this name.
           */
          int length;
  
          NameImpl(SharedNameTable table) {
              super(table);
          }
  
          @Override
          public int getIndex() {
              return index;
          }
  
          @Override
          public int getByteLength() {
              return length;
          }
  
          @Override
          public byte getByteAt(int i) {
              return getByteArray()[index + i];
          }
  
          @Override
          public byte[] getByteArray() {
              return ((SharedNameTable) table).bytes;
          }
  
          @Override
          public int getByteOffset() {
              return index;
          }
  
          /** Return the hash value of this name.
           */
          @DefinedBy(Api.LANGUAGE_MODEL)
          public int hashCode() {
              return index;
          }
  
          /** Is this name equal to other?
           */
          @DefinedBy(Api.LANGUAGE_MODEL)
          public boolean equals(Object other) {
              if (other instanceof Name)
                  return
                      table == ((Name)other).table && index == ((Name) other).getIndex();
              else return false;
          }
  
      }
  
  }
  