com.sleepycat.util

Class PackedInteger

java.lang.Object

com.sleepycat.util.PackedInteger

public class PackedInteger
extends java.lang.Object

Static methods for reading and writing packed integers.

Note that packed integers are not sorted naturally for a byte-by-byte comparison because they have a preceding length and are little endian; therefore, they are typically not used for keys.

Values in the inclusive range [-119,119] are stored in a single byte. For values outside that range, the first byte stores the sign and the number of additional bytes. The additional bytes store (abs(value) - 119) as an unsigned little endian integer.

To read and write packed integer values, call readInt(byte[], int) and writeInt(byte[], int, int) or for long values readLong(byte[], int) and writeLong(byte[], int, long). To get the length of a packed integer without reading it, call getReadIntLength(byte[], int) or getReadLongLength(byte[], int). To get the length of an unpacked integer without writing it, call getWriteIntLength(int) or getWriteLongLength(long).

Because the same packed format is used for int and long values, stored int values may be expanded to long values without introducing a format incompatibility. You can treat previously stored packed int values as long values by calling readLong(byte[], int) and getReadLongLength(byte[], int).

Author:

Mark Hayes

Field Summary

Fields

Modifier and Type	Field and Description
static int	MAX_LENGTH The maximum number of bytes needed to store an int value (5).
static int	MAX_LONG_LENGTH The maximum number of bytes needed to store a long value (9).

Constructor Summary

Constructors

Constructor and Description
PackedInteger()

Method Summary

Methods

Modifier and Type	Method and Description
static int	getReadIntLength(byte[] buf, int off) Returns the number of bytes that would be read by readInt(byte[], int).
static int	getReadLongLength(byte[] buf, int off) Returns the number of bytes that would be read by readLong(byte[], int).
static int	getWriteIntLength(int value) Returns the number of bytes that would be written by writeInt(byte[], int, int).
static int	getWriteLongLength(long value) Returns the number of bytes that would be written by writeLong(byte[], int, long).
static int	readInt(byte[] buf, int off) Reads a packed integer at the given buffer offset and returns it.
static long	readLong(byte[] buf, int off) Reads a packed long integer at the given buffer offset and returns it.
static int	writeInt(byte[] buf, int offset, int value) Writes a packed integer starting at the given buffer offset and returns the next offset to be written.
static int	writeLong(byte[] buf, int offset, long value) Writes a packed long integer starting at the given buffer offset and returns the next offset to be written.

Methods inherited from class java.lang.Object

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

Field Detail

MAX_LENGTH

public static final int MAX_LENGTH

The maximum number of bytes needed to store an int value (5).

See Also:

Constant Field Values

MAX_LONG_LENGTH

public static final int MAX_LONG_LENGTH

The maximum number of bytes needed to store a long value (9).

See Also:

Constant Field Values

Constructor Detail

PackedInteger

public PackedInteger()

Method Detail

readInt

public static int readInt(byte[] buf,
          int off)

Reads a packed integer at the given buffer offset and returns it.

Parameters:

buf - the buffer to read from.

off - the offset in the buffer at which to start reading.

Returns:

the integer that was read.

readLong

public static long readLong(byte[] buf,
            int off)

Reads a packed long integer at the given buffer offset and returns it.

Parameters:

buf - the buffer to read from.

off - the offset in the buffer at which to start reading.

Returns:

the long integer that was read.

getReadIntLength

public static int getReadIntLength(byte[] buf,
                   int off)

Returns the number of bytes that would be read by readInt(byte[], int).

Because the length is stored in the first byte, this method may be called with only the first byte of the packed integer in the given buffer. This method only accesses one byte at the given offset.

Parameters:

buf - the buffer to read from.

off - the offset in the buffer at which to start reading.

Returns:

the number of bytes that would be read.

getReadLongLength

public static int getReadLongLength(byte[] buf,
                    int off)

Returns the number of bytes that would be read by readLong(byte[], int).

Because the length is stored in the first byte, this method may be called with only the first byte of the packed integer in the given buffer. This method only accesses one byte at the given offset.

Parameters:

buf - the buffer to read from.

off - the offset in the buffer at which to start reading.

Returns:

the number of bytes that would be read.

writeInt

public static int writeInt(byte[] buf,
           int offset,
           int value)

Writes a packed integer starting at the given buffer offset and returns the next offset to be written.

Parameters:

buf - the buffer to write to.

offset - the offset in the buffer at which to start writing.

value - the integer to be written.

Returns:

the offset past the bytes written.

writeLong

public static int writeLong(byte[] buf,
            int offset,
            long value)

Writes a packed long integer starting at the given buffer offset and returns the next offset to be written.

Parameters:

buf - the buffer to write to.

offset - the offset in the buffer at which to start writing.

value - the long integer to be written.

Returns:

the offset past the bytes written.

getWriteIntLength

public static int getWriteIntLength(int value)

Returns the number of bytes that would be written by writeInt(byte[], int, int).

Parameters:

value - the integer to be written.

Returns:

the number of bytes that would be used to write the given integer.

getWriteLongLength

public static int getWriteLongLength(long value)

Returns the number of bytes that would be written by writeLong(byte[], int, long).

Parameters:

value - the long integer to be written.

Returns:

the number of bytes that would be used to write the given long integer.