package org.jscsi.target.util;

 /**

  * A utility class with static methods for accessing individual bits of bytes.

  * <p>

  * The value of a single bit can be easily retrieved with the {@link #getBit(byte, int)} method.

  * <p>

  * Setting a bit is a little bit more complicated. The byte to be changed must be set to the return value of

  * {@link #getByteWithBitSet(byte, int, boolean)}.

  * 

  * @author Andreas Ergenzinger

  */

 public final class BitManip {

     /**

      * Sets a single bit. If the <i>value</i> parameter is <code>true</code>, the bit will be set to <code>one</code>,

      * and to <code>zero</code> otherwise. All other bits will be left unchanged.

      * <p>

      * The bits are numbered in big-endian format, from 0 (LSB) to 7 (MSB).

      * <p>

      * <code>          

      * +---+---+---+---+---+---+---+---+<br>

      * | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | bit number<br> 

      * +---+---+---+---+---+---+---+---+<br>

      * </code>

      * 

      * @param b the original byte value

      * @param bitNumber the big-endian position of the bit to be changed, from 0 to 7

      * @param value <code>true</code> for <i>1</i>, <code>false</code> for <i>0</i>

      * @return the edited byte value

      */

     public static final byte getByteWithBitSet (final byte b, final int bitNumber, final boolean value) {

         int number = b;

         if (value) {

             // make sure bit is set to true

             int mask = 1;

             mask <<= bitNumber;

             number |= mask;

         } else {

             int mask = 1;

             mask <<= bitNumber;

             mask ^= 255;// flip bits

             number &= mask;

         }

         return (byte) number;

     }

     /**

      * Returns <code>true</code>, if the bit at the given position is set to <code>one</code> and <code>false</code> if

      * it is set to <code>zero</code> . The bits are numbered in big-endian format, from 0 (LSB) to 7 (MSB).

      * <p>

      * <code>

      * +---+---+---+---+---+---+---+---+<br>

      * | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | bit number<br> 

      * +---+---+---+---+---+---+---+---+<br>

      * </code>

      * 

      * @param b the byte value in question

      * @param bitNumber the big-endian position of the bit to be changed, from 0 to 7

      * @return <code>true</code> if bit is set to <code>one</code>, else <code>false</code>

      */

     public static boolean getBit (final byte b, final int bitNumber) {

         int number = b;

         number >>>= bitNumber;

         number &= 1;

         if (number == 1) return true;

         return false;

     }

 }