mathutils.java

pastry的java实现的2.0b版

/*************************************************************************

"FreePastry" Peer-to-Peer Application Development Substrate 

Copyright 2002, Rice University. All rights reserved.

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********************************************************************************/
package rice.p2p.util;

import java.io.*;
import java.math.*;
import java.util.*;

import rice.environment.random.RandomSource;

/**
 * This class contains a large number of static methods for performing math
 * operations.
 *
 * @version $Id: MathUtils.java 2551 2005-06-06 19:01:02Z jeffh $
 * @author amislove
 */
public class MathUtils {

  /**
   * The array used for conversion to hexidecimal
   */
  public final static char[] HEX_ARRAY = new char[]{'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};

  /**
   * Make the constructor private so no MathUtils is ever created.
   */
  private MathUtils() {
  }

  /**
   * Utility method for converting a char to a byte
   *
   * @param c The char
   * @return The byte
   */
  protected static byte getByte(char c) {
    if ((c >= '0') && (c <= '9')) {
      return (byte) (c - '0');
    } else if ((c >= 'A') && (c <= 'F')) {
      return (byte) (10 + (byte) (c - 'A'));
    } else if ((c >= 'a') && (c <= 'f')) {
      return (byte) (10 + (byte) (c - 'a'));
    } else {
      throw new RuntimeException("Could not decode hex character '" + c + "'");
    }
  }

  /**
   * Utility which does *proper* modding, where the result is guaranteed to be
   * positive.
   *
   * @param a The modee
   * @param b The value to mod by
   * @return The result
   */
  public static int mod(int a, int b) {
    return ((a % b) + b) % b;
  }

  /**
   * Utility method which xors two given byte arrays, of equal length, and
   * returns the results
   *
   * @param a The first array
   * @param b The second array
   * @return A new byte array, xored
   */
  public static byte[] xor(byte[] a, byte[] b) {
    byte[] result = new byte[a.length];

    for (int i = 0; i < result.length; i++) {
      result[i] = (byte) (a[i] ^ b[i]);
    }

    return result;
  }

  /**
   * Method which returns a specified number of random bytes
   *
   * @param len The number of random bytes to generate
   * @param random DESCRIBE THE PARAMETER
   * @return DESCRIBE THE RETURN VALUE
   */
  public static byte[] randomBytes(int len, RandomSource random) {
    byte[] result = new byte[len];
    random.nextBytes(result);

    return result;
  }

  /**
   * Method which returns a random int
   *
   * @param random DESCRIBE THE PARAMETER
   * @return DESCRIBE THE RETURN VALUE
   */
  public static int randomInt(RandomSource random) {
    return random.nextInt();
  }

  /**
   * Utility method which converts a byte[] to a hexidecimal string of
   * characters, in lower case
   *
   * @param text The array to convert
   * @return A string representation
   */
  public static String toHex(byte[] text) {
    StringBuffer buffer = new StringBuffer();

    for (int i = 0; i < text.length; i++) {
      buffer.append(HEX_ARRAY[0x0f & (text[i] >> 4)]);
      buffer.append(HEX_ARRAY[0x0f & text[i]]);
    }

    return buffer.toString();
  }

  /**
   * Utility method which converts a hex string to a byte[]
   *
   * @param text The text to convert
   * @return The bytes
   */
  public static byte[] fromHex(String text) {
    byte[] result = new byte[text.length() / 2];

    for (int i = 0; i < result.length; i++) {
      result[i] = (byte) ((byte) ((byte) 0xf0 & ((getByte(text.charAt(2 * i))) << 4)) | getByte(text.charAt(2 * i + 1)));
    }

    return result;
  }

  /**
   * Utility method for converting a int into a byte[]
   *
   * @param input The log to convert
   * @return a byte[] representation
   */
  public static byte[] intToByteArray(int input) {
    byte[] output = new byte[4];
    intToByteArray(input, output, 0);
    return output;
  }

  /**
   * Utility method for converting a int into a byte[]
   *
   * @param input The log to convert
   * @param output DESCRIBE THE PARAMETER
   * @param offset DESCRIBE THE PARAMETER
   */
  public static void intToByteArray(int input, byte[] output, int offset) {
    output[offset + 0] = (byte) (0xFF & (input >> 24));
    output[offset + 1] = (byte) (0xFF & (input >> 16));
    output[offset + 2] = (byte) (0xFF & (input >> 8));
    output[offset + 3] = (byte) (0xFF & input);
  }

  /**
   * Utility method for converting a byte[] into a int
   *
   * @param input The byte[] to convert
   * @return a int representation
   */
  public static int byteArrayToInt(byte[] input) {
    input = correctLength(input, 4);

    int result;
    result = (input[0] & 0xFF) << 24;
    result |= (input[1] & 0xFF) << 16;
    result |= (input[2] & 0xFF) << 8;
    result |= (input[3] & 0xFF);

    return result;
  }

  /**
   * Utility method for converting a long into a byte[]
   *
   * @param input The log to convert
   * @return a byte[] representation
   */
  public static byte[] longToByteArray(long input) {
    byte[] output = new byte[8];
    longToByteArray(input, output, 0);
    return output;
  }

  /**
   * Utility method for converting a long into a byte[]
   *
   * @param input The log to convert
   * @param output DESCRIBE THE PARAMETER
   * @param offset DESCRIBE THE PARAMETER
   */
  public static void longToByteArray(long input, byte[] output, int offset) {
    output[offset + 0] = (byte) (0xFF & (input >> 56));
    output[offset + 1] = (byte) (0xFF & (input >> 48));
    output[offset + 2] = (byte) (0xFF & (input >> 40));
    output[offset + 3] = (byte) (0xFF & (input >> 32));
    output[offset + 4] = (byte) (0xFF & (input >> 24));
    output[offset + 5] = (byte) (0xFF & (input >> 16));
    output[offset + 6] = (byte) (0xFF & (input >> 8));
    output[offset + 7] = (byte) (0xFF & input);
  }

  /**
   * Utility method for converting a byte[] into a long
   *
   * @param input The byte[] to convert
   * @return a long representation
   */
  public static long byteArrayToLong(byte[] input) {
    input = correctLength(input, 8);

    long result;
    result = ((long) (input[0] & 0xFF)) << 56;
    result |= ((long) (input[1] & 0xFF)) << 48;
    result |= ((long) (input[2] & 0xFF)) << 40;
    result |= ((long) (input[3] & 0xFF)) << 32;
    result |= ((long) (input[4] & 0xFF)) << 24;
    result |= ((long) (input[5] & 0xFF)) << 16;
    result |= ((long) (input[6] & 0xFF)) << 8;
    result |= ((long) (input[7] & 0xFF));

    return result;
  }

  /**
   * Utility method for ensuring the array is of the proper length. THis method
   * enforces the length by appending 0's or returning a subset of the input
   * array.
   *
   * @param data The input array
   * @param length The length the array should be
   * @return A correct-length array
   */
  private static byte[] correctLength(byte[] data, int length) {
    if (data.length >= length) {
      return data;
    }

    byte[] result = new byte[length];

    for (int i = 0; (i < data.length) && (i < result.length); i++) {
      result[i] = data[i];
    }

    return result;
  }
}