Package org.eclipse.rdf4j.sail.lmdb

Class Varint

java.lang.Object

org.eclipse.rdf4j.sail.lmdb.Varint

public final class Varint
extends Object

Encodes and decodes unsigned values using variable-length encoding.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	Varint.GroupMatcher	A matcher for partial equality tests of varint lists.

Method Summary

Modifier and Type	Method	Description
static int	calcLengthUnsigned(long value)	Calculates required length in bytes to encode the given long value using variable-length encoding.
static int	calcListLengthUnsigned(long a, long b, long c, long d)	Calculates required length in bytes to encode a list of four long values using variable-length encoding.
static int	firstToLength(byte a0)	Determines length of an encoded varint value by inspecting the first byte.
static long	readListElementUnsigned(ByteBuffer bb, int index)	Decodes a single element of a list of variable-length long values from a buffer.
static void	readListUnsigned(ByteBuffer bb, int[] indexMap, long[] values)	Decodes multiple values using variable-length encoding from the given buffer.
static void	readListUnsigned(ByteBuffer bb, long[] values)	Decodes multiple values using variable-length encoding from the given buffer.
static long	readUnsigned(ByteBuffer bb)	Decodes a value using the variable-length encoding of SQLite.
static long	readUnsigned(ByteBuffer bb, int pos)	Decodes a value using the variable-length encoding of SQLite.
static void	writeListUnsigned(ByteBuffer bb, long[] values)	Encodes multiple values using variable-length encoding into the given buffer.
static void	writeUnsigned(ByteBuffer bb, long value)	Encodes a value using the variable-length encoding of SQLite.

Methods inherited from class java.lang.Object

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

Method Detail

writeUnsigned

public static void writeUnsigned(ByteBuffer bb,
                                 long value)

Encodes a value using the variable-length encoding of SQLite.

The encoding has the following properties:

1. Smaller (and more common) values use fewer bytes and take up less space than larger (and less common) values.
2. The length of any varint can be determined by looking at just the first byte of the encoding.
3. Lexicographical and numeric ordering for varints are the same. Hence if a group of varints are ordered lexicographically (that is to say, if they are ordered by Arrays.compare(byte[], byte[]) with shorter varints coming first) then those varints will also be in numeric order. This property means that varints can be used as keys in the key/value backend storage and the records will occur in numerical order of the keys.

A0	Value
0–240	A0
241–248	240 + 256 × (A0 – 241) + A1
249	2288 + 256 × A1 + A2
250	A1…A3 as a 3-byte big-endian integer
251	A1…A4 as a 4-byte big-endian integer
252	A1…A5 as a 5-byte big-endian integer
253	A1…A6 as a 6-byte big-endian integer
254	A1…A7 as a 7-byte big-endian integer
255	A1…A8 as a 8-byte big-endian integer

Parameters:

bb - buffer for writing bytes

value - value to encode

calcLengthUnsigned

public static int calcLengthUnsigned(long value)

Calculates required length in bytes to encode the given long value using variable-length encoding.

Parameters:

value - the value value

Returns:

length in bytes

calcListLengthUnsigned

public static int calcListLengthUnsigned(long a,
                                         long b,
                                         long c,
                                         long d)

Calculates required length in bytes to encode a list of four long values using variable-length encoding.

Parameters:

a - first value

b - second value

c - third value

d - fourth value

Returns:

length in bytes

readUnsigned

public static long readUnsigned(ByteBuffer bb)
                         throws IllegalArgumentException

Decodes a value using the variable-length encoding of SQLite.

Parameters:

bb - buffer for reading bytes

Returns:

decoded value

Throws:

IllegalArgumentException - if encoded varint is longer than 9 bytes

See Also:

writeUnsigned(ByteBuffer, long)

readUnsigned

public static long readUnsigned(ByteBuffer bb,
                                int pos)
                         throws IllegalArgumentException

Decodes a value using the variable-length encoding of SQLite.

Parameters:

bb - buffer for reading bytes

Returns:

decoded value

Throws:

IllegalArgumentException - if encoded varint is longer than 9 bytes

See Also:

writeUnsigned(ByteBuffer, long)

firstToLength

public static int firstToLength(byte a0)

Determines length of an encoded varint value by inspecting the first byte.

Parameters:

a0 - first byte of varint value

Returns:

decoded value

readListElementUnsigned

public static long readListElementUnsigned(ByteBuffer bb,
                                           int index)

Decodes a single element of a list of variable-length long values from a buffer.

Parameters:

bb - buffer for reading bytes

index - the element's index

Returns:

the decoded value

writeListUnsigned

public static void writeListUnsigned(ByteBuffer bb,
                                     long[] values)

Encodes multiple values using variable-length encoding into the given buffer.

Parameters:

bb - buffer for writing bytes

values - array with values to write

readListUnsigned

public static void readListUnsigned(ByteBuffer bb,
                                    long[] values)

Decodes multiple values using variable-length encoding from the given buffer.

Parameters:

bb - buffer for writing bytes

values - array for the result values

readListUnsigned

public static void readListUnsigned(ByteBuffer bb,
                                    int[] indexMap,
                                    long[] values)

Decodes multiple values using variable-length encoding from the given buffer.

Parameters:

bb - buffer for writing bytes

indexMap - map for indexes of values within values array

values - array for the result values