1 package org.jscsi.target.util;
2
3 /**
4 * A utility class with static methods for accessing individual bits of bytes.
5 * <p>
6 * The value of a single bit can be easily retrieved with the {@link #getBit(byte, int)} method.
7 * <p>
8 * Setting a bit is a little bit more complicated. The byte to be changed must be set to the return value of
9 * {@link #getByteWithBitSet(byte, int, boolean)}.
10 *
11 * @author Andreas Ergenzinger
12 */
13 public final class BitManip {
14
15 /**
16 * Sets a single bit. If the <i>value</i> parameter is <code>true</code>, the bit will be set to <code>one</code>,
17 * and to <code>zero</code> otherwise. All other bits will be left unchanged.
18 * <p>
19 * The bits are numbered in big-endian format, from 0 (LSB) to 7 (MSB).
20 * <p>
21 * <code>
22 * +---+---+---+---+---+---+---+---+<br>
23 * | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | bit number<br>
24 * +---+---+---+---+---+---+---+---+<br>
25 * </code>
26 *
27 * @param b the original byte value
28 * @param bitNumber the big-endian position of the bit to be changed, from 0 to 7
29 * @param value <code>true</code> for <i>1</i>, <code>false</code> for <i>0</i>
30 * @return the edited byte value
31 */
32 public static final byte getByteWithBitSet (final byte b, final int bitNumber, final boolean value) {
33
34 int number = b;
35
36 if (value) {
37 // make sure bit is set to true
38 int mask = 1;
39 mask <<= bitNumber;
40 number |= mask;
41 } else {
42 int mask = 1;
43 mask <<= bitNumber;
44 mask ^= 255;// flip bits
45 number &= mask;
46 }
47
48 return (byte) number;
49 }
50
51 /**
52 * Returns <code>true</code>, if the bit at the given position is set to <code>one</code> and <code>false</code> if
53 * it is set to <code>zero</code> . The bits are numbered in big-endian format, from 0 (LSB) to 7 (MSB).
54 * <p>
55 * <code>
56 * +---+---+---+---+---+---+---+---+<br>
57 * | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | bit number<br>
58 * +---+---+---+---+---+---+---+---+<br>
59 * </code>
60 *
61 * @param b the byte value in question
62 * @param bitNumber the big-endian position of the bit to be changed, from 0 to 7
63 * @return <code>true</code> if bit is set to <code>one</code>, else <code>false</code>
64 */
65 public static boolean getBit (final byte b, final int bitNumber) {
66 int number = b;
67 number >>>= bitNumber;
68 number &= 1;
69 if (number == 1) return true;
70 return false;
71 }
72 }