content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF 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 org.apache.arrow.memory.util;
  
  import org.apache.arrow.memory.ArrowBuf;
  import org.apache.arrow.memory.util.hash.ArrowBufHasher;
  import org.apache.arrow.memory.util.hash.SimpleHasher;
  import org.apache.arrow.util.Preconditions;
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /**
   * Pointer to a memory region within an {@link ArrowBuf}. It will be used as the basis for
   * calculating hash code within a vector, and equality determination.
   */
  public final class ArrowBufPointer implements Comparable<ArrowBufPointer> {
  
    /** The hash code when the arrow buffer is null. */
    public static final int NULL_HASH_CODE = 0;
  
    private @Nullable ArrowBuf buf;
  
    private long offset;
  
    private long length;
  
    private int hashCode = NULL_HASH_CODE;
  
    private final ArrowBufHasher hasher;
  
    /** A flag indicating if the underlying memory region has changed. */
    private boolean hashCodeChanged = false;
  
    /** The default constructor. */
    public ArrowBufPointer() {
      this(SimpleHasher.INSTANCE);
    }
  
    /**
     * Constructs an arrow buffer pointer with the specified hasher.
     *
     * @param hasher the hasher to use.
     */
    public ArrowBufPointer(ArrowBufHasher hasher) {
      Preconditions.checkNotNull(hasher);
      this.hasher = hasher;
      this.buf = null;
    }
  
    /**
     * Constructs an Arrow buffer pointer.
     *
     * @param buf the underlying {@link ArrowBuf}, which can be null.
     * @param offset the start off set of the memory region pointed to.
     * @param length the length off set of the memory region pointed to.
     */
    public ArrowBufPointer(ArrowBuf buf, long offset, long length) {
      this(buf, offset, length, SimpleHasher.INSTANCE);
    }
  
    /**
     * Constructs an Arrow buffer pointer.
     *
     * @param buf the underlying {@link ArrowBuf}, which can be null.
     * @param offset the start off set of the memory region pointed to.
     * @param length the length off set of the memory region pointed to.
     * @param hasher the hasher used to calculate the hash code.
     */
    public ArrowBufPointer(ArrowBuf buf, long offset, long length, ArrowBufHasher hasher) {
      Preconditions.checkNotNull(hasher);
      this.hasher = hasher;
      set(buf, offset, length);
    }
  
    /**
     * Sets this pointer.
     *
     * @param buf the underlying {@link ArrowBuf}, which can be null.
     * @param offset the start off set of the memory region pointed to.
     * @param length the length off set of the memory region pointed to.
     */
    public void set(ArrowBuf buf, long offset, long length) {
      this.buf = buf;
      this.offset = offset;
      this.length = length;
  
      hashCodeChanged = true;
    }
  
    /**
     * Gets the underlying buffer, or null if the underlying data is invalid or null.
     *
     * @return the underlying buffer, if any, or null if the underlying data is invalid or null.
     */
    public @Nullable ArrowBuf getBuf() {
      return buf;
    }
  
    public long getOffset() {
      return offset;
    }
  
    public long getLength() {
      return length;
    }
  
    @Override
    public boolean equals(@Nullable Object o) {
      if (this == o) {
        return true;
      }
      if (o == null || getClass() != o.getClass()) {
        return false;
      }
  
      if (!hasher.equals(((ArrowBufPointer) o).hasher)) {
        // note that the hasher is incorporated in equality determination
        // this is to avoid problems in cases where two Arrow buffer pointers are not equal
        // while having different hashers and equal hash codes.
        return false;
      }
  
      ArrowBufPointer other = (ArrowBufPointer) o;
      if (buf == null || other.buf == null) {
        if (buf == null && other.buf == null) {
          return true;
        } else {
          return false;
        }
      }
  
      return ByteFunctionHelpers.equal(
              buf, offset, offset + length, other.buf, other.offset, other.offset + other.length)
          != 0;
    }
  
    @Override
    public int hashCode() {
      if (!hashCodeChanged) {
        return hashCode;
      }
  
      // re-compute the hash code
      if (buf == null) {
        hashCode = NULL_HASH_CODE;
      } else {
        hashCode = hasher.hashCode(buf, offset, length);
      }
  
      hashCodeChanged = false;
      return hashCode;
    }
  
    /**
     * Compare two arrow buffer pointers. The comparison is based on lexicographic order.
     *
     * @param that the other pointer to compare.
     * @return 0 if the two pointers are equal; a positive integer if this pointer is larger; a
     *     negative integer if this pointer is smaller.
     */
    @Override
    public int compareTo(ArrowBufPointer that) {
      if (this.buf == null || that.buf == null) {
        if (this.buf == null && that.buf == null) {
          return 0;
        } else {
          // null is smaller
          return this.buf == null ? -1 : 1;
        }
      }
  
      return ByteFunctionHelpers.compare(
          this.buf,
          this.offset,
          this.offset + this.length,
          that.buf,
          that.offset,
          that.offset + that.length);
    }
  }
  