Package 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

  • Field Details

  • Method Details

    • 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)

    • longToPrefixCodedBytes

      public static void longToPrefixCodedBytes(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

    • intToPrefixCodedBytes

      public static void intToPrefixCodedBytes(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

    • 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:

    • 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:

    • 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

      public static double sortableLongToDouble(long val)
      Converts a sortable long back to a double.
      See Also:

    • 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

      public static float sortableIntToFloat(int val)
      Converts a sortable int back to a float.
      See Also:

    • 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.

    • filterPrefixCodedLongs

      public static TermsEnum filterPrefixCodedLongs(TermsEnum termsEnum)
      Filters the given TermsEnum by accepting only prefix coded 64 bit terms with a shift value of 0.
      Parameters:
      termsEnum - the terms enum to filter
      Returns:
      a filtered TermsEnum that only returns prefix coded 64 bit terms with a shift value of 0.

    • filterPrefixCodedInts

      public static TermsEnum filterPrefixCodedInts(TermsEnum termsEnum)
      Filters the given TermsEnum by accepting only prefix coded 32 bit terms with a shift value of 0.
      Parameters:
      termsEnum - the terms enum to filter
      Returns:
      a filtered TermsEnum that only returns prefix coded 32 bit terms with a shift value of 0.