CodecUtils.java

/**
 * Copyright 2014 National University of Ireland, Galway.
 *
 * This file is part of the SIREn project. Project and contact information:
 *
 *  https://github.com/rdelbru/SIREn
 *
 * 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.sindice.siren.util;

import java.nio.ByteBuffer;

import org.apache.lucene.store.IndexInput;
import org.apache.lucene.util.BytesRef;

/**
 * Contains methods to encode an integer into a byte array and decode a byte
 * array into an integer.
 */
public class CodecUtils {

  /**
   * Convert a byte array to an int (32bit word).
   *
   * @param src The byte array (length = 4)
   * @param offset The offset of the encoded integer in the byte array
   * @return The integer
   */
  public static int byteArrayToInt(final byte[] src, final int offset) {
    int value = 0;
    for (int i = offset; i < offset + 4; i++) {
      value += (src[i] & 0x000000FF) << (4 - 1 - i) * 8;
    }
    return value;
  }

  /**
   * Convert an integer to a byte array.
   *
   * @param x The integer
   * @param dst The byte array (length = 4)
   * @param offset The offset of the encoded integer in the byte array
   */
  public static final void intToByteArray(final int x, final byte[] dst, final int offset) {
    dst[offset + 3] = (byte) (x & 0x000000ff);
    dst[offset + 2] = (byte) ((x & 0x0000ff00) >>> 8);
    dst[offset + 1] = (byte) ((x & 0x00ff0000) >>> 16);
    dst[offset + 0] = (byte) ((x & 0xff000000) >>> 24);
  }

  /**
   * Writes an integer in a variable-length format. Writes between one and
   * five bytes. Smaller values take fewer bytes. Negative numbers are not
   * supported.
   * @see IndexInput#readVInt()
   */
  public static void vIntToByteArray(int i, final ByteBuffer bb) {
    while ((i & ~0x7F) != 0) {
      bb.put((byte) ((i & 0x7f) | 0x80));
      i >>>= 7;
    }
    bb.put((byte) i);
  }

  /**
   * Reads an int stored in variable-length format. Reads between one and five
   * bytes. Smaller values take fewer bytes. Negative numbers are not supported.
   */
  public static int byteArrayToVInt(final BytesRef ref) {
    byte b = ref.bytes[ref.offset++];
    int i = b & 0x7F;
    for (int shift = 7; (b & 0x80) != 0; shift += 7) {
      b = ref.bytes[ref.offset++];
      i |= (b & 0x7F) << shift;
    }
    return i;
  }

  /**
   * Writes an integer in a variable-length format. Writes between one and
   * five bytes. Smaller values take fewer bytes. Negative numbers are not
   * supported.
   * @see IndexInput#readVInt()
   */
  public static void appendVInt(int i, final BytesRef ref) {
    while ((i & ~0x7F) != 0) {
      ref.bytes[ref.offset++] = (byte) ((i & 0x7f) | 0x80);
      i >>>= 7;
    }
    ref.bytes[ref.offset++] = (byte) i;
  }

  /**
   * Write the content, i.e. bits, of a byte into the string buffer.
   * </br>
   * Code taken from Lucene-1410.
   *
   * @param b The byte
   * @param buf the string buffer
   */
  private static void writeBits(final int b, final StringBuffer buf) {
    for (int i = 7; i >= 0; i--) {
      buf.append((b >>> i) & 1);
    }
  }

  /**
   * Display the content, i.e. bits, of a byte array. Write to stdout the
   * content of the array on a single line.
   * </br>
   * Code taken from Lucene-1410.
   *
   * @param array The byte array
   */
  public static void writeBytes(final byte[] array) {
    final StringBuffer buf = new StringBuffer();
    for (final byte element : array) {
      CodecUtils.writeBits(element & 255, buf);
      buf.append(' ');
    }
    System.out.println(buf);
  }

  /**
   * Display the content, i.e. bits, of a byte array. Write to stdout 4 bytes
   * per lines.
   * </br>
   * Code taken from Lucene-1410.
   *
   * @param array The byte array
   */
  public static void writeIndentBytes(final byte[] array) {
    final StringBuffer buf = new StringBuffer();
    for (int i = 0; i < array.length; i++) {
      CodecUtils.writeBits(array[i] & 255, buf);
      if (((i+1) % 4) != 0) {
        buf.append(' ');
      } else {
        System.out.println(buf);
        buf.setLength(0);
      }
    }
  }

}