org.gridfour.compress

Class CodecM32

java.lang.Object

org.gridfour.compress.CodecM32

public class CodecM32
extends Object

Provides utilities for coding integer values into a series of one or more by values using the Martin coding scheme.

The M32 coding scheme provides a way of encoding standard integer values into a sequence of between 1 and 5 bytes, depending on the magnitude of the input value. The scheme is advantageous integer distributions with substantially more one-byte values than multi-byte values. In fact, for values greater than 126 or less than -126, the resulting storage will be at least 2 bytes. And values greater than 254 or less than -254, require at least 3 bytes. So for those integers that could be represented by the two-byte "short" data type, this method is actually disadvantageous.

The M32 coding scheme resembles the variable-length integer coding scheme used in SQLLite, except that it supports both positive and negative integer values.

Field Summary

Fields

Modifier and Type	Field and Description
static int	MAX_BYTES_PER_VALUE The maximum number of bytes that would be needed to encode large-magnitude symbols

Constructor Summary

Constructors

Constructor and Description
CodecM32(byte[] buffer, int offset, int length) Construct an instance using the specified buffer for storing data.
CodecM32(int symbolCount) Construct an instance with a buffer large enough to hold the specified number of integer values.

Method Summary

Modifier and Type	Method and Description
int	decode() Decodes the next value in the buffer, advancing the buffer position as appropriate.
void	encode(int value) Encodes the specified value and appends it to the buffer.
int	getEncodedLength() Gets the the length of the encoded data stored in the buffer
byte[]	getEncoding() Get a safe copy of the content of the buffer.
int	remaining() Gets the number of bytes remaining in the buffer.
void	rewind() Reset the buffer position to its beginning position

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

MAX_BYTES_PER_VALUE

public static final int MAX_BYTES_PER_VALUE

The maximum number of bytes that would be needed to encode large-magnitude symbols

See Also:

Constant Field Values

Constructor Detail

CodecM32

public CodecM32(int symbolCount)

Construct an instance with a buffer large enough to hold the specified number of integer values.

Parameters:

symbolCount - the number of values to be stored in the buffer.

CodecM32

public CodecM32(byte[] buffer,
                int offset,
                int length)

Construct an instance using the specified buffer for storing data.

Parameters:

buffer - a valid byte array dimensioned to at least offset+length

offset - the starting position for storing data in the buffer.

length - the limit of the number bytes to be stored in the buffer.

Method Detail

rewind

public void rewind()

Reset the buffer position to its beginning position

getEncoding

public byte[] getEncoding()

Get a safe copy of the content of the buffer.

Returns:

an array of size zero or greater.

getEncodedLength

public int getEncodedLength()

Gets the the length of the encoded data stored in the buffer

Returns:

a positive integer, potentially zero

encode

public void encode(int value)

Encodes the specified value and appends it to the buffer. The buffer position is advanced by the number of bytes needed for the encoding.

Because this method is written to be used in tight loops with intense processing, there is no bounds checking performed on the internal buffer. Application developers must take responsibility for their own safety of implementation issues.

Parameters:

value - any integer value to be encoded (a signed integer that can be stored with 6 bytes)

decode

public int decode()

Decodes the next value in the buffer, advancing the buffer position as appropriate.

Because this method is written to be used in tight loops with intense processing, there is no bounds checking performed on the internal buffer.

Returns:

an arbitrary integer value.

remaining

public int remaining()

Gets the number of bytes remaining in the buffer. This is not the number of symbols remaining, but rather the available bytes.

Returns:

a positive value, potentially zero.