code: /*
   * 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.commons.io;
  
  import java.io.EOFException;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.OutputStream;
  
  /**
   * Utility code for dealing with different endian systems.
   * <p>
   * Different computer architectures adopt different conventions for
   * byte ordering. In so-called "Little Endian" architectures (eg Intel),
   * the low-order byte is stored in memory at the lowest address, and
   * subsequent bytes at higher addresses. For "Big Endian" architectures
   * (eg Motorola), the situation is reversed.
   * This class helps you solve this incompatability.
   * <p>
   * Origin of code: Excalibur
   *
   * @author <a href="mailto:peter@apache.org">Peter Donald</a>
   * @version $Id: EndianUtils.java 539632 2007-05-18 23:37:59Z bayard $
   * @see org.apache.commons.io.input.SwappedDataInputStream
   */
  public class EndianUtils {
  
      /**
       * Instances should NOT be constructed in standard programming.
       */
      public EndianUtils() {
          super();
      }
  
      // ========================================== Swapping routines
  
      /**
       * Converts a "short" value between endian systems.
       * @param value value to convert
       * @return the converted value
       */
      public static short swapShort(short value) {
          return (short) ( ( ( ( value >> 0 ) & 0xff ) << 8 ) +
              ( ( ( value >> 8 ) & 0xff ) << 0 ) );
      }
  
      /**
       * Converts a "int" value between endian systems.
       * @param value value to convert
       * @return the converted value
       */
      public static int swapInteger(int value) {
          return
              ( ( ( value >> 0 ) & 0xff ) << 24 ) +
              ( ( ( value >> 8 ) & 0xff ) << 16 ) +
              ( ( ( value >> 16 ) & 0xff ) << 8 ) +
              ( ( ( value >> 24 ) & 0xff ) << 0 );
      }
  
      /**
       * Converts a "long" value between endian systems.
       * @param value value to convert
       * @return the converted value
       */
      public static long swapLong(long value) {
          return
              ( ( ( value >> 0 ) & 0xff ) << 56 ) +
              ( ( ( value >> 8 ) & 0xff ) << 48 ) +
              ( ( ( value >> 16 ) & 0xff ) << 40 ) +
              ( ( ( value >> 24 ) & 0xff ) << 32 ) +
              ( ( ( value >> 32 ) & 0xff ) << 24 ) +
              ( ( ( value >> 40 ) & 0xff ) << 16 ) +
              ( ( ( value >> 48 ) & 0xff ) << 8 ) +
              ( ( ( value >> 56 ) & 0xff ) << 0 );
      }
  
      /**
       * Converts a "float" value between endian systems.
       * @param value value to convert
       * @return the converted value
       */
      public static float swapFloat(float value) {
          return Float.intBitsToFloat( swapInteger( Float.floatToIntBits( value ) ) );
      }
  
      /**
       * Converts a "double" value between endian systems.
       * @param value value to convert
       * @return the converted value
       */
      public static double swapDouble(double value) {
          return Double.longBitsToDouble( swapLong( Double.doubleToLongBits( value ) ) );
      }
  
      // ========================================== Swapping read/write routines
  
      /**
       * Writes a "short" value to a byte array at a given offset. The value is
       * converted to the opposed endian system while writing.
       * @param data target byte array
       * @param offset starting offset in the byte array
       * @param value value to write
       */
      public static void writeSwappedShort(byte[] data, int offset, short value) {
          data[ offset + 0 ] = (byte)( ( value >> 0 ) & 0xff );
          data[ offset + 1 ] = (byte)( ( value >> 8 ) & 0xff );
      }
  
      /**
       * Reads a "short" value from a byte array at a given offset. The value is
       * converted to the opposed endian system while reading.
       * @param data source byte array
       * @param offset starting offset in the byte array
       * @return the value read
       */
      public static short readSwappedShort(byte[] data, int offset) {
          return (short)( ( ( data[ offset + 0 ] & 0xff ) << 0 ) +
              ( ( data[ offset + 1 ] & 0xff ) << 8 ) );
      }
  
      /**
       * Reads an unsigned short (16-bit) value from a byte array at a given
       * offset. The value is converted to the opposed endian system while
       * reading.
       * @param data source byte array
       * @param offset starting offset in the byte array
       * @return the value read
       */
      public static int readSwappedUnsignedShort(byte[] data, int offset) {
          return ( ( ( data[ offset + 0 ] & 0xff ) << 0 ) +
              ( ( data[ offset + 1 ] & 0xff ) << 8 ) );
      }
  
      /**
       * Writes a "int" value to a byte array at a given offset. The value is
       * converted to the opposed endian system while writing.
       * @param data target byte array
       * @param offset starting offset in the byte array
       * @param value value to write
       */
      public static void writeSwappedInteger(byte[] data, int offset, int value) {
          data[ offset + 0 ] = (byte)( ( value >> 0 ) & 0xff );
          data[ offset + 1 ] = (byte)( ( value >> 8 ) & 0xff );
          data[ offset + 2 ] = (byte)( ( value >> 16 ) & 0xff );
          data[ offset + 3 ] = (byte)( ( value >> 24 ) & 0xff );
      }
  
      /**
       * Reads a "int" value from a byte array at a given offset. The value is
       * converted to the opposed endian system while reading.
       * @param data source byte array
       * @param offset starting offset in the byte array
       * @return the value read
       */
      public static int readSwappedInteger(byte[] data, int offset) {
          return ( ( ( data[ offset + 0 ] & 0xff ) << 0 ) +
              ( ( data[ offset + 1 ] & 0xff ) << 8 ) +
              ( ( data[ offset + 2 ] & 0xff ) << 16 ) +
              ( ( data[ offset + 3 ] & 0xff ) << 24 ) );
      }
  
      /**
       * Reads an unsigned integer (32-bit) value from a byte array at a given
       * offset. The value is converted to the opposed endian system while
       * reading.
       * @param data source byte array
       * @param offset starting offset in the byte array
       * @return the value read
       */
      public static long readSwappedUnsignedInteger(byte[] data, int offset) {
          long low = ( ( ( data[ offset + 0 ] & 0xff ) << 0 ) +
                       ( ( data[ offset + 1 ] & 0xff ) << 8 ) +
                       ( ( data[ offset + 2 ] & 0xff ) << 16 ) );
  
          long high = data[ offset + 3 ] & 0xff;
  
          return (high << 24) + (0xffffffffL & low); 
      }
  
      /**
       * Writes a "long" value to a byte array at a given offset. The value is
       * converted to the opposed endian system while writing.
       * @param data target byte array
       * @param offset starting offset in the byte array
       * @param value value to write
       */
      public static void writeSwappedLong(byte[] data, int offset, long value) {
          data[ offset + 0 ] = (byte)( ( value >> 0 ) & 0xff );
          data[ offset + 1 ] = (byte)( ( value >> 8 ) & 0xff );
          data[ offset + 2 ] = (byte)( ( value >> 16 ) & 0xff );
          data[ offset + 3 ] = (byte)( ( value >> 24 ) & 0xff );
          data[ offset + 4 ] = (byte)( ( value >> 32 ) & 0xff );
          data[ offset + 5 ] = (byte)( ( value >> 40 ) & 0xff );
          data[ offset + 6 ] = (byte)( ( value >> 48 ) & 0xff );
          data[ offset + 7 ] = (byte)( ( value >> 56 ) & 0xff );
      }
  
      /**
       * Reads a "long" value from a byte array at a given offset. The value is
       * converted to the opposed endian system while reading.
       * @param data source byte array
       * @param offset starting offset in the byte array
       * @return the value read
       */
      public static long readSwappedLong(byte[] data, int offset) {
          long low = 
              ( ( data[ offset + 0 ] & 0xff ) << 0 ) +
              ( ( data[ offset + 1 ] & 0xff ) << 8 ) +
              ( ( data[ offset + 2 ] & 0xff ) << 16 ) +
              ( ( data[ offset + 3 ] & 0xff ) << 24 );
          long high = 
              ( ( data[ offset + 4 ] & 0xff ) << 0 ) +
              ( ( data[ offset + 5 ] & 0xff ) << 8 ) +
              ( ( data[ offset + 6 ] & 0xff ) << 16 ) +
              ( ( data[ offset + 7 ] & 0xff ) << 24 );
          return (high << 32) + (0xffffffffL & low); 
      }
  
      /**
       * Writes a "float" value to a byte array at a given offset. The value is
       * converted to the opposed endian system while writing.
       * @param data target byte array
       * @param offset starting offset in the byte array
       * @param value value to write
       */
      public static void writeSwappedFloat(byte[] data, int offset, float value) {
          writeSwappedInteger( data, offset, Float.floatToIntBits( value ) );
      }
  
      /**
       * Reads a "float" value from a byte array at a given offset. The value is
       * converted to the opposed endian system while reading.
       * @param data source byte array
       * @param offset starting offset in the byte array
       * @return the value read
       */
      public static float readSwappedFloat(byte[] data, int offset) {
          return Float.intBitsToFloat( readSwappedInteger( data, offset ) );
      }
  
      /**
       * Writes a "double" value to a byte array at a given offset. The value is
       * converted to the opposed endian system while writing.
       * @param data target byte array
       * @param offset starting offset in the byte array
       * @param value value to write
       */
      public static void writeSwappedDouble(byte[] data, int offset, double value) {
          writeSwappedLong( data, offset, Double.doubleToLongBits( value ) );
      }
  
      /**
       * Reads a "double" value from a byte array at a given offset. The value is
       * converted to the opposed endian system while reading.
       * @param data source byte array
       * @param offset starting offset in the byte array
       * @return the value read
       */
      public static double readSwappedDouble(byte[] data, int offset) {
          return Double.longBitsToDouble( readSwappedLong( data, offset ) );
      }
  
      /**
       * Writes a "short" value to an OutputStream. The value is
       * converted to the opposed endian system while writing.
       * @param output target OutputStream
       * @param value value to write
       * @throws IOException in case of an I/O problem
       */
      public static void writeSwappedShort(OutputStream output, short value)
          throws IOException
      {
          output.write( (byte)( ( value >> 0 ) & 0xff ) );
          output.write( (byte)( ( value >> 8 ) & 0xff ) );
      }
  
      /**
       * Reads a "short" value from an InputStream. The value is
       * converted to the opposed endian system while reading.
       * @param input source InputStream
       * @return the value just read
       * @throws IOException in case of an I/O problem
       */
      public static short readSwappedShort(InputStream input)
          throws IOException
      {
          return (short)( ( ( read( input ) & 0xff ) << 0 ) +
              ( ( read( input ) & 0xff ) << 8 ) );
      }
  
      /**
       * Reads a unsigned short (16-bit) from an InputStream. The value is
       * converted to the opposed endian system while reading.
       * @param input source InputStream
       * @return the value just read
       * @throws IOException in case of an I/O problem
       */
      public static int readSwappedUnsignedShort(InputStream input)
          throws IOException
      {
          int value1 = read( input );
          int value2 = read( input );
  
          return ( ( ( value1 & 0xff ) << 0 ) +
              ( ( value2 & 0xff ) << 8 ) );
      }
  
      /**
       * Writes a "int" value to an OutputStream. The value is
       * converted to the opposed endian system while writing.
       * @param output target OutputStream
       * @param value value to write
       * @throws IOException in case of an I/O problem
       */
      public static void writeSwappedInteger(OutputStream output, int value)
          throws IOException
      {
          output.write( (byte)( ( value >> 0 ) & 0xff ) );
          output.write( (byte)( ( value >> 8 ) & 0xff ) );
          output.write( (byte)( ( value >> 16 ) & 0xff ) );
          output.write( (byte)( ( value >> 24 ) & 0xff ) );
      }
  
      /**
       * Reads a "int" value from an InputStream. The value is
       * converted to the opposed endian system while reading.
       * @param input source InputStream
       * @return the value just read
       * @throws IOException in case of an I/O problem
       */
      public static int readSwappedInteger(InputStream input)
          throws IOException
      {
          int value1 = read( input );
          int value2 = read( input );
          int value3 = read( input );
          int value4 = read( input );
  
          return ( ( value1 & 0xff ) << 0 ) +
              ( ( value2 & 0xff ) << 8 ) +
              ( ( value3 & 0xff ) << 16 ) +
              ( ( value4 & 0xff ) << 24 );
      }
  
      /**
       * Reads a unsigned integer (32-bit) from an InputStream. The value is
       * converted to the opposed endian system while reading.
       * @param input source InputStream
       * @return the value just read
       * @throws IOException in case of an I/O problem
       */
      public static long readSwappedUnsignedInteger(InputStream input)
          throws IOException
      {
          int value1 = read( input );
          int value2 = read( input );
          int value3 = read( input );
          int value4 = read( input );
  
          long low = ( ( ( value1 & 0xff ) << 0 ) +
                       ( ( value2 & 0xff ) << 8 ) +
                       ( ( value3 & 0xff ) << 16 ) );
  
          long high = value4 & 0xff;
  
          return (high << 24) + (0xffffffffL & low); 
      }
  
      /**
       * Writes a "long" value to an OutputStream. The value is
       * converted to the opposed endian system while writing.
       * @param output target OutputStream
       * @param value value to write
       * @throws IOException in case of an I/O problem
       */
      public static void writeSwappedLong(OutputStream output, long value)
          throws IOException
      {
          output.write( (byte)( ( value >> 0 ) & 0xff ) );
          output.write( (byte)( ( value >> 8 ) & 0xff ) );
          output.write( (byte)( ( value >> 16 ) & 0xff ) );
          output.write( (byte)( ( value >> 24 ) & 0xff ) );
          output.write( (byte)( ( value >> 32 ) & 0xff ) );
          output.write( (byte)( ( value >> 40 ) & 0xff ) );
          output.write( (byte)( ( value >> 48 ) & 0xff ) );
          output.write( (byte)( ( value >> 56 ) & 0xff ) );
      }
  
      /**
       * Reads a "long" value from an InputStream. The value is
       * converted to the opposed endian system while reading.
       * @param input source InputStream
       * @return the value just read
       * @throws IOException in case of an I/O problem
       */
      public static long readSwappedLong(InputStream input)
          throws IOException
      {
          byte[] bytes = new byte[8];
          for ( int i=0; i<8; i++ ) {
              bytes[i] = (byte) read( input );
          }
          return readSwappedLong( bytes, 0 );
      }
  
      /**
       * Writes a "float" value to an OutputStream. The value is
       * converted to the opposed endian system while writing.
       * @param output target OutputStream
       * @param value value to write
       * @throws IOException in case of an I/O problem
       */
      public static void writeSwappedFloat(OutputStream output, float value)
          throws IOException
      {
          writeSwappedInteger( output, Float.floatToIntBits( value ) );
      }
  
      /**
       * Reads a "float" value from an InputStream. The value is
       * converted to the opposed endian system while reading.
       * @param input source InputStream
       * @return the value just read
       * @throws IOException in case of an I/O problem
       */
      public static float readSwappedFloat(InputStream input)
          throws IOException
      {
          return Float.intBitsToFloat( readSwappedInteger( input ) );
      }
  
      /**
       * Writes a "double" value to an OutputStream. The value is
       * converted to the opposed endian system while writing.
       * @param output target OutputStream
       * @param value value to write
       * @throws IOException in case of an I/O problem
       */
      public static void writeSwappedDouble(OutputStream output, double value)
          throws IOException
      {
          writeSwappedLong( output, Double.doubleToLongBits( value ) );
      }
  
      /**
       * Reads a "double" value from an InputStream. The value is
       * converted to the opposed endian system while reading.
       * @param input source InputStream
       * @return the value just read
       * @throws IOException in case of an I/O problem
       */
      public static double readSwappedDouble(InputStream input)
          throws IOException
      {
          return Double.longBitsToDouble( readSwappedLong( input ) );
      }
  
      /**
       * Reads the next byte from the input stream.
       * @param input  the stream
       * @return the byte
       * @throws IOException if the end of file is reached
       */
      private static int read(InputStream input)
          throws IOException
      {
          int value = input.read();
  
          if( -1 == value ) {
              throw new EOFException( "Unexpected EOF reached" );
          }
  
          return value;
      }
  }
  