org.apache.lucene.util

Class NumericUtils

java.lang.Object

org.apache.lucene.util.NumericUtils

public final class NumericUtils
extends Object

This is a helper class to generate prefix-encoded representations for numerical values and supplies converters to represent float/double values as sortable integers/longs.

To quickly execute range queries in Apache Lucene, a range is divided recursively into multiple intervals for searching: The center of the range is searched only with the lowest possible precision in the trie, while the boundaries are matched more exactly. This reduces the number of terms dramatically.

This class generates terms to achieve this: First the numerical integer values need to be converted to bytes. For that integer values (32 bit or 64 bit) are made unsigned and the bits are converted to ASCII chars with each 7 bit. The resulting byte[] is sortable like the original integer value (even using UTF-8 sort order). Each value is also prefixed (in the first char) by the shift value (number of bits removed) used during encoding.

To also index floating point numbers, this class supplies two methods to convert them to integer values by changing their bit layout: doubleToSortableLong(double), floatToSortableInt(float). You will have no precision loss by converting floating point numbers to integers and back (only that the integer form is not usable). Other data types like dates can easily converted to longs or ints (e.g. date to long: Date.getTime()).

For easy usage, the trie algorithm is implemented for indexing inside NumericTokenStream that can index int, long, float, and double. For querying, NumericRangeQuery and NumericRangeFilter implement the query part for the same data types.

This class can also be used, to generate lexicographically sortable (according to BytesRef.getUTF8SortedAsUTF16Comparator()) representations of numeric data types for other usages (e.g. sorting).

Since:

2.9, API changed non backwards-compliant in 4.0

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

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	NumericUtils.IntRangeBuilder Callback for splitIntRange(org.apache.lucene.util.NumericUtils.IntRangeBuilder, int, int, int).
static class	NumericUtils.LongRangeBuilder Callback for splitLongRange(org.apache.lucene.util.NumericUtils.LongRangeBuilder, int, long, long).

Field Summary

Fields

Modifier and Type	Field and Description
static int	BUF_SIZE_INT The maximum term length (used for byte[] buffer size) for encoding int values.
static int	BUF_SIZE_LONG The maximum term length (used for byte[] buffer size) for encoding long values.
static int	PRECISION_STEP_DEFAULT The default precision step used by IntField, FloatField, LongField, DoubleField, NumericTokenStream, NumericRangeQuery, and NumericRangeFilter.
static byte	SHIFT_START_INT Integers are stored at lower precision by shifting off lower bits.
static byte	SHIFT_START_LONG Longs are stored at lower precision by shifting off lower bits.

Method Summary

Methods

Modifier and Type	Method and Description
static long	doubleToSortableLong(double val) Converts a double value to a sortable signed long.
static int	floatToSortableInt(float val) Converts a float value to a sortable signed int.
static int	getPrefixCodedIntShift(BytesRef val) Returns the shift value from a prefix encoded int.
static int	getPrefixCodedLongShift(BytesRef val) Returns the shift value from a prefix encoded long.
static int	intToPrefixCoded(int val, int shift, BytesRef bytes) Returns prefix coded bits after reducing the precision by shift bits.
static int	longToPrefixCoded(long val, int shift, BytesRef bytes) Returns prefix coded bits after reducing the precision by shift bits.
static int	prefixCodedToInt(BytesRef val) Returns an int from prefixCoded bytes.
static long	prefixCodedToLong(BytesRef val) Returns a long from prefixCoded bytes.
static float	sortableIntToFloat(int val) Converts a sortable int back to a float.
static double	sortableLongToDouble(long val) Converts a sortable long back to a double.
static void	splitIntRange(NumericUtils.IntRangeBuilder builder, int precisionStep, int minBound, int maxBound) Splits an int range recursively.
static void	splitLongRange(NumericUtils.LongRangeBuilder builder, int precisionStep, long minBound, long maxBound) Splits a long range recursively.

Methods inherited from class java.lang.Object

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

Field Detail

PRECISION_STEP_DEFAULT

public static final int PRECISION_STEP_DEFAULT

The default precision step used by IntField, FloatField, LongField, DoubleField, NumericTokenStream, NumericRangeQuery, and NumericRangeFilter.

See Also:

Constant Field Values

SHIFT_START_LONG

public static final byte SHIFT_START_LONG

Longs are stored at lower precision by shifting off lower bits. The shift count is stored as SHIFT_START_LONG+shift in the first byte

See Also:

Constant Field Values

BUF_SIZE_LONG

public static final int BUF_SIZE_LONG

The maximum term length (used for byte[] buffer size) for encoding long values.

See Also:

longToPrefixCoded(long,int,BytesRef), Constant Field Values

SHIFT_START_INT

public static final byte SHIFT_START_INT

Integers are stored at lower precision by shifting off lower bits. The shift count is stored as SHIFT_START_INT+shift in the first byte

See Also:

Constant Field Values

BUF_SIZE_INT

public static final int BUF_SIZE_INT

The maximum term length (used for byte[] buffer size) for encoding int values.

See Also:

intToPrefixCoded(int,int,BytesRef), Constant Field Values

Method Detail

longToPrefixCoded

public static int longToPrefixCoded(long val,
                    int shift,
                    BytesRef bytes)

Returns prefix coded bits after reducing the precision by shift bits. This is method is used by NumericTokenStream. After encoding, bytes.offset will always be 0.

Parameters:

val - the numeric value

shift - how many bits to strip from the right

bytes - will contain the encoded value

Returns:

the hash code for indexing (TermsHash)

intToPrefixCoded

public static int intToPrefixCoded(int val,
                   int shift,
                   BytesRef bytes)

Returns prefix coded bits after reducing the precision by shift bits. This is method is used by NumericTokenStream. After encoding, bytes.offset will always be 0.

Parameters:

val - the numeric value

shift - how many bits to strip from the right

bytes - will contain the encoded value

Returns:

the hash code for indexing (TermsHash)

getPrefixCodedLongShift

public static int getPrefixCodedLongShift(BytesRef val)

Returns the shift value from a prefix encoded long.

Throws:

NumberFormatException - if the supplied BytesRef is not correctly prefix encoded.

getPrefixCodedIntShift

public static int getPrefixCodedIntShift(BytesRef val)

Returns the shift value from a prefix encoded int.

Throws:

NumberFormatException - if the supplied BytesRef is not correctly prefix encoded.

prefixCodedToLong

public static long prefixCodedToLong(BytesRef val)

Returns a long from prefixCoded bytes. Rightmost bits will be zero for lower precision codes. This method can be used to decode a term's value.

Throws:

NumberFormatException - if the supplied BytesRef is not correctly prefix encoded.

See Also:

longToPrefixCoded(long,int,BytesRef)

prefixCodedToInt

public static int prefixCodedToInt(BytesRef val)

Returns an int from prefixCoded bytes. Rightmost bits will be zero for lower precision codes. This method can be used to decode a term's value.

Throws:

NumberFormatException - if the supplied BytesRef is not correctly prefix encoded.

See Also:

intToPrefixCoded(int,int,BytesRef)

doubleToSortableLong

public static long doubleToSortableLong(double val)

Converts a double value to a sortable signed long. The value is converted by getting their IEEE 754 floating-point "double format" bit layout and then some bits are swapped, to be able to compare the result as long. By this the precision is not reduced, but the value can easily used as a long. The sort order (including Double.NaN) is defined by Double.compareTo(java.lang.Double); NaN is greater than positive infinity.

See Also:

sortableLongToDouble(long)

sortableLongToDouble

public static double sortableLongToDouble(long val)

Converts a sortable long back to a double.

See Also:

doubleToSortableLong(double)

floatToSortableInt

public static int floatToSortableInt(float val)

Converts a float value to a sortable signed int. The value is converted by getting their IEEE 754 floating-point "float format" bit layout and then some bits are swapped, to be able to compare the result as int. By this the precision is not reduced, but the value can easily used as an int. The sort order (including Float.NaN) is defined by Float.compareTo(java.lang.Float); NaN is greater than positive infinity.

See Also:

sortableIntToFloat(int)

sortableIntToFloat

public static float sortableIntToFloat(int val)

Converts a sortable int back to a float.

See Also:

floatToSortableInt(float)

splitLongRange

public static void splitLongRange(NumericUtils.LongRangeBuilder builder,
                  int precisionStep,
                  long minBound,
                  long maxBound)

Splits a long range recursively. You may implement a builder that adds clauses to a BooleanQuery for each call to its NumericUtils.LongRangeBuilder.addRange(BytesRef,BytesRef) method.

This method is used by NumericRangeQuery.

splitIntRange

public static void splitIntRange(NumericUtils.IntRangeBuilder builder,
                 int precisionStep,
                 int minBound,
                 int maxBound)

Splits an int range recursively. You may implement a builder that adds clauses to a BooleanQuery for each call to its NumericUtils.IntRangeBuilder.addRange(BytesRef,BytesRef) method.

This method is used by NumericRangeQuery.