com.datadoghq.sketch.ddsketch.encoding

Class VarEncodingHelper

java.lang.Object

com.datadoghq.sketch.ddsketch.encoding.VarEncodingHelper

public final class VarEncodingHelper
extends java.lang.Object

Method Summary

Modifier and Type	Method and Description
static long	decodeSignedVarLong(Input input) decodeSignedVarLong deserializes long values that have been encoded using encodeSignedVarLong(Output, long).
static long	decodeUnsignedVarLong(Input input) decodeUnsignedVarLong deserializes long values that have been encoded using encodeUnsignedVarLong(Output, long).
static double	decodeVarDouble(Input input) decodeSignedVarLong deserializes double values that have been encoded using encodeVarDouble(Output, double).
static void	encodeSignedVarLong(Output output, long value) encodeSignedVarLong serializes long values using zig-zag encoding, which ensures small-scale integers are turned into integers that have leading zeros, whether they are positive or negative, hence allows for space-efficient encoding of those values.
static void	encodeUnsignedVarLong(Output output, long value) encodeUnsignedVarLong serializes long values 7 bits at a time, starting with the least significant bits.
static void	encodeVarDouble(Output output, double value) encodeVarDouble serializes double values using a method that is similar to the varint encoding and that is space-efficient for non-negative integer values.
static byte	signedVarLongEncodedLength(long value) signedVarLongEncodedLength returns the number of bytes that encodeSignedVarLong(Output, long) encodes a long value into.
static byte	unsignedVarLongEncodedLength(long value) unsignedVarLongEncodedLength returns the number of bytes that encodeUnsignedVarLong(Output, long) encodes a long value into.
static byte	varDoubleEncodedLength(double value) varDoubleEncodedLength returns the number of bytes that encodeVarDouble(Output, double) encodes a double value into.

Methods inherited from class java.lang.Object

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

Method Detail

encodeUnsignedVarLong

public static void encodeUnsignedVarLong(Output output,
                                         long value)
                                  throws java.io.IOException

encodeUnsignedVarLong serializes long values 7 bits at a time, starting with the least significant bits. The most significant bit in each output byte is the continuation bit and indicates whether there are additional non-zero bits encoded in following bytes. There are at most 9 output bytes and the last one does not have a continuation bit, allowing for it to encode 8 bits (\(8*7+8 = 64\)).

Parameters:

output - what to write to

value - the value to encode

Throws:

java.io.IOException - if an IOException is thrown while writing to output

decodeUnsignedVarLong

public static long decodeUnsignedVarLong(Input input)
                                  throws java.io.IOException

decodeUnsignedVarLong deserializes long values that have been encoded using encodeUnsignedVarLong(Output, long).

Parameters:

input - what to read from

Returns:

the decoded value

Throws:

java.io.IOException - if an IOException is thrown while reading from input

unsignedVarLongEncodedLength

public static byte unsignedVarLongEncodedLength(long value)

unsignedVarLongEncodedLength returns the number of bytes that encodeUnsignedVarLong(Output, long) encodes a long value into.

Parameters:

value - the value to encode

Returns:

the number of bytes that encodeUnsignedVarLong(Output, long) encodes a long value into

encodeSignedVarLong

public static void encodeSignedVarLong(Output output,
                                       long value)
                                throws java.io.IOException

encodeSignedVarLong serializes long values using zig-zag encoding, which ensures small-scale integers are turned into integers that have leading zeros, whether they are positive or negative, hence allows for space-efficient encoding of those values.

Parameters:

output - what to write to

value - the value to encode

Throws:

java.io.IOException - if an IOException is thrown while writing to output

decodeSignedVarLong

public static long decodeSignedVarLong(Input input)
                                throws java.io.IOException

decodeSignedVarLong deserializes long values that have been encoded using encodeSignedVarLong(Output, long).

Parameters:

input - what to read from

Returns:

the decoded value

Throws:

java.io.IOException - if an IOException is thrown while reading from input

signedVarLongEncodedLength

public static byte signedVarLongEncodedLength(long value)

signedVarLongEncodedLength returns the number of bytes that encodeSignedVarLong(Output, long) encodes a long value into.

Parameters:

value - the value to encode

Returns:

the number of bytes that encodeSignedVarLong(Output, long) encodes a long value into

encodeVarDouble

public static void encodeVarDouble(Output output,
                                   double value)
                            throws java.io.IOException

encodeVarDouble serializes double values using a method that is similar to the varint encoding and that is space-efficient for non-negative integer values. The output takes at most 9 bytes.

Input values are first shifted as floating-point values (+1), then transmuted to integer values, then shifted again as integer values (-Double.doubleToRawLongBits(1)). That is in order to minimize the number of non-zero bits when dealing with non-negative integer values.

After that transformation, any input integer value no greater than \(2^{53}\) (the largest integer value that can be encoded exactly as a 64-bit floating-point value) will have at least 6 leading zero bits. By rotating bits to the left, those bits end up at the right of the binary representation.

The resulting bits are then encoded similarly to the varint method, but starting with the most significant bits.

Parameters:

output - what to write to

value - the value to encode

Throws:

java.io.IOException - if an IOException is thrown while writing to output

decodeVarDouble

public static double decodeVarDouble(Input input)
                              throws java.io.IOException

decodeSignedVarLong deserializes double values that have been encoded using encodeVarDouble(Output, double).

Parameters:

input - what to read from

Returns:

the decoded value

Throws:

java.io.IOException - if an IOException is thrown while reading from input

varDoubleEncodedLength

public static byte varDoubleEncodedLength(double value)

varDoubleEncodedLength returns the number of bytes that encodeVarDouble(Output, double) encodes a double value into.

Parameters:

value - the value to encode

Returns:

the number of bytes that encodeVarDouble(Output, double) encodes a double value into