org.apache.lucene.util

Class SmallFloat

java.lang.Object

org.apache.lucene.util.SmallFloat

public class SmallFloat
extends Object

Floating point numbers smaller than 32 bits.

NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

Method Summary

Modifier and Type	Method and Description
static float	byte315ToFloat(byte b) byteToFloat(b, mantissaBits=3, zeroExponent=15)
static int	byte4ToInt(byte b) Decode values that have been encoded with intToByte4(int).
static float	byteToFloat(byte b, int numMantissaBits, int zeroExp) Converts an 8 bit float to a 32 bit float.
static byte	floatToByte(float f, int numMantissaBits, int zeroExp) Converts a 32 bit float to an 8 bit float.
static byte	floatToByte315(float f) floatToByte(b, mantissaBits=3, zeroExponent=15) smallest non-zero value = 5.820766E-10 largest value = 7.5161928E9 epsilon = 0.125
static long	int4ToLong(int i) Decode values encoded with longToInt4(long).
static byte	intToByte4(int i) Encode an integer to a byte.
static int	longToInt4(long i) Float-like encoding for positive longs that preserves ordering and 4 significant bits.

Methods inherited from class java.lang.Object

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

Method Detail

floatToByte

public static byte floatToByte(float f,
                               int numMantissaBits,
                               int zeroExp)

Converts a 32 bit float to an 8 bit float.
Values less than zero are all mapped to zero.
Values are truncated (rounded down) to the nearest 8 bit value.
Values between zero and the smallest representable value are rounded up.

Parameters:

f - the 32 bit float to be converted to an 8 bit float (byte)

numMantissaBits - the number of mantissa bits to use in the byte, with the remainder to be used in the exponent

zeroExp - the zero-point in the range of exponent values

Returns:

the 8 bit float representation

byteToFloat

public static float byteToFloat(byte b,
                                int numMantissaBits,
                                int zeroExp)

Converts an 8 bit float to a 32 bit float.

floatToByte315

public static byte floatToByte315(float f)

floatToByte(b, mantissaBits=3, zeroExponent=15)
smallest non-zero value = 5.820766E-10
largest value = 7.5161928E9
epsilon = 0.125

byte315ToFloat

public static float byte315ToFloat(byte b)

byteToFloat(b, mantissaBits=3, zeroExponent=15)

longToInt4

public static int longToInt4(long i)

Float-like encoding for positive longs that preserves ordering and 4 significant bits.

int4ToLong

public static final long int4ToLong(int i)

Decode values encoded with longToInt4(long).

intToByte4

public static byte intToByte4(int i)

Encode an integer to a byte. It is built upon longToInt4(long) and leverages the fact that longToInt4(Integer.MAX_VALUE) is less than 255 to encode low values more accurately.

byte4ToInt

public static int byte4ToInt(byte b)

Decode values that have been encoded with intToByte4(int).