00010101 11101101 11010xxx* *
Where the "xxx" represents three bits that should be ignored, and
* can have any value.
*
* @author Casey Marshall (rsdio@metastatic.org)
*/
public class BitString implements Cloneable, Comparable, java.io.Serializable
{
// Fields.
// ------------------------------------------------------------------------
/** The bits themselves. */
private final byte[] bytes;
/**
* The exportable byte array. This array has the ignored bits
* removed.
*/
private transient byte[] externBytes;
/** The number of bits ignored at the end of the byte array. */
private final int ignoredBits;
/** This bit string as a boolean array. */
private transient boolean[] boolVal;
// Constructors.
// ------------------------------------------------------------------------
/**
* Create a new bit string, shifting the given byte array if needed.
*
* @param bytes The byte array holding the bit string.
* @param ignoredBits The number of bits to ignore.
* @param doShift Pass true in this parameter if the byte array has
* not yet been shifted left by ignoredBits.
* @throws IllegalArgumentException If ignoredBits is negative
* or greater than 7.
* @throws NullPointerException If bytes is null.
*/
public BitString(byte[] bytes, int ignoredBits, boolean doShift)
{
this(bytes, 0, bytes.length, ignoredBits, doShift);
}
/**
* Create a new bit string, shifting the given byte array if needed.
*
* @param bytes The byte array holding the bit string.
* @param offset The offset where the meaningful bytes begin.
* @param length The number of meaningful bytes.
* @param ignoredBits The number of bits to ignore.
* @param doShift Pass true in this parameter if the byte array has
* not yet been shifted left by ignoredBits.
* @throws IllegalArgumentException If ignoredBits is negative
* or greater than 7.
* @throws NullPointerException If bytes is null.
*/
public BitString(byte[] bytes, int offset, int length,
int ignoredBits, boolean doShift)
{
if (ignoredBits < 0 || ignoredBits > 7)
throw new IllegalArgumentException();
if (bytes == null)
throw new NullPointerException();
if (doShift && ignoredBits > 0)
{
this.externBytes = new byte[length];
System.arraycopy(bytes, offset, externBytes, 0, length);
this.bytes = new BigInteger(externBytes).shiftLeft(ignoredBits)
.toByteArray();
}
else
{
this.bytes = new byte[length];
System.arraycopy(bytes, offset, this.bytes, 0, length);
}
this.ignoredBits = ignoredBits;
}
/**
* Create a new bit string.
*
* @param bytes The byte array holding the bit string.
* @param offset The offset where the meaningful bytes begin.
* @param length The number of meaningful bytes.
* @param ignoredBits The number of bits to ignore.
* @throws IllegalArgumentException If ignoredBits is negative
* or greater than 7.
* @throws NullPointerException If bytes is null.
*/
public BitString(byte[] bytes, int offset, int length, int ignoredBits)
{
this(bytes, offset, length, ignoredBits, false);
}
/**
* Create a new bit string.
*
* @param bytes The byte array holding the bit string.
* @param ignoredBits The number of bits to ignore.
* @throws IllegalArgumentException If ignoredBits is negative
* or greater than 7.
* @throws NullPointerException If bytes is null.
*/
public BitString(byte[] bytes, int ignoredBits)
{
this(bytes, 0, bytes.length, ignoredBits, false);
}
/**
* Create a new bit string.
*
* @param bytes The byte array holding the bit string.
* @param offset The offset where the meaningful bytes begin.
* @param length The number of meaningful bytes.
* @throws NullPointerException If bytes is null.
*/
public BitString(byte[] bytes, int offset, int length)
{
this(bytes, offset, length, 0, false);
}
/**
* Create a new bit string.
*
* @param bytes The byte array holding the bit string.
* @throws NullPointerException If bytes is null.
*/
public BitString(byte[] bytes)
{
this(bytes, 0, bytes.length, 0, false);
}
// Instance methods.
// ------------------------------------------------------------------------
/**
* Return this bit string as a byte array, with the ignored bits
* trimmed off. The byte array is cloned every time this method is
* called to prevent modification.
*
* @return The trimmed byte array.
*/
public byte[] toByteArray()
{
if (ignoredBits == 0)
return (byte[]) bytes.clone();
if (externBytes == null)
externBytes = new BigInteger(bytes).shiftRight(ignoredBits).toByteArray();
return (byte[]) externBytes.clone();
}
/**
* Returns this bit string as a byte array, with the ignored bits
* present. The byte array is cloned every time this method is
* called to prevent modification.
*
* @return The byte array.
*/
public byte[] getShiftedByteArray()
{
return (byte[]) bytes.clone();
}
/**
* Returns the number of ignored bits.
*
* @return The number of ignored bits.
*/
public int getIgnoredBits()
{
return ignoredBits;
}
/**
* Returns the size, in bits, of this bit string.
*
* @return The size of this bit string.
*/
public int size()
{
return (bytes.length << 3) - ignoredBits;
}
/**
* Return this bit string as a boolean array. The value returned is of
* size {@link #size()}, and each true value
* corresponding to each "1" in this bit string. The boolean array is
* cloned before it is returned.
*
* @return The boolean array.
*/
public boolean[] toBooleanArray()
{
if (boolVal == null)
{
boolVal = new boolean[size()];
for (int i = 0, j = 7, k = 0; i < boolVal.length; i++)
{
boolVal[i] = (bytes[k] & 1 << j--) != 0;
if (j < 0)
{
j = 7;
k++;
}
}
}
return (boolean[]) boolVal.clone();
}
public Object clone()
{
try
{
return super.clone();
}
catch (CloneNotSupportedException cce)
{
throw new InternalError(cce.getMessage());
}
}
public int compareTo(Object o)
{
BitString that = (BitString) o;
if (this.equals(that))
return 0;
if (this.bytes.length != that.bytes.length)
return (this.bytes.length < that.bytes.length) ? -1 : 1;
if (this.ignoredBits != that.ignoredBits)
return (this.ignoredBits < that.ignoredBits) ? -1 : 1;
for (int i = 0; i < this.bytes.length; i++)
if (this.bytes[i] != that.bytes[i])
return (this.bytes[i] < that.bytes[i]) ? -1 : 1;
return 0; // not reached.
}
public boolean equals(Object o)
{
if (this == o)
return true;
BitString that = (BitString) o;
// True for cloned instances.
if (this.bytes == that.bytes && this.ignoredBits == that.ignoredBits)
return true;
if (this.ignoredBits == that.ignoredBits)
return Arrays.equals(this.bytes, that.bytes);
return false;
}
public String toString()
{
StringBuffer sb = new StringBuffer();
for (int i = 0, j = 7, k = 0; i < size(); i++)
{
sb.append((bytes[k] & 1 << j) != 0 ? "1" : "0");
j--;
if (j < 0)
{
j = 7;
k++;
}
}
return sb.toString();
}
}