Package org.basex.util

Class Num

java.lang.Object
org.basex.util.Num
public final class Num extends Object

This class provides operations to compress and decompress 4-byte integer values in byte arrays in order to save memory.

The first two bits of a Num array indicate the range of the compressed number:

  • 00: the number (0x00-0x3F) is encoded in the remaining 6 bits of the current byte
  • 01: the number (0x40-0x3FFF) is encoded in 14 bits of the current and the following byte
  • 10: the number (0x4000-0x3FFFFFFF) is encoded in 30 bits of the current and the following three bytes
  • 11: the number (0x40000000-0xFFFFFFFF) is encoded in 32 bits of the following four bytes
Author:
BaseX Team 2005-21, BSD License, Christian Gruen

  • Method Summary

    Modifier and Type
    Method
    Description
    static byte[]
    add(byte[] array, int value)
    Compresses and adds a value to the specified array and returns the resulting array.
    static int
    get(byte[] array, int pos)
    Decompresses and returns a value from the specified byte array.
    static int
    length(byte[] array, int pos)
    Returns the compressed length of the value at the specified position.
    static int
    length(int v)
    Returns the compressed length of the specified value.
    static byte[]
    newNum(int value)
    Creates a new number array, in which the first four bytes contain the number of occupied bytes.
    static byte[]
    num(int value)
    Creates a compressed representation of the specified value.
    static int
    set(byte[] array, int value)
    Compresses and stores an integer value at the beginning of the byte array.
    static int
    size(byte[] array)
    Returns the length value of the specified array, stored in the first four bytes.
    static void
    size(byte[] array, int length)
    Stores the specified length value in the first bytes of the specified array.
    static String
    toString(byte[] num)
    Returns a string representation of the specified number array.

    Methods inherited from class java.lang.Object

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

  • Method Details

    • newNum

      public static byte[] newNum(int value)
      Creates a new number array, in which the first four bytes contain the number of occupied bytes.
      Parameters:
      value - initial value to be compressed and stored
      Returns:
      new number array

    • num

      public static byte[] num(int value)
      Creates a compressed representation of the specified value.
      Parameters:
      value - value to be compressed
      Returns:
      new number array

    • add

      public static byte[] add(byte[] array, int value)
      Compresses and adds a value to the specified array and returns the resulting array.
      Parameters:
      array - input array
      value - value to be added
      Returns:
      resulting array (may be the same as input array)

    • get

      public static int get(byte[] array, int pos)
      Decompresses and returns a value from the specified byte array.
      Parameters:
      array - array
      pos - position where the value is found
      Returns:
      decompressed value

    • set

      public static int set(byte[] array, int value)
      Compresses and stores an integer value at the beginning of the byte array.
      Parameters:
      array - array
      value - value to be stored
      Returns:
      length

    • size

      public static int size(byte[] array)
      Returns the length value of the specified array, stored in the first four bytes.
      Parameters:
      array - input array
      Returns:
      array length

    • size

      public static void size(byte[] array, int length)
      Stores the specified length value in the first bytes of the specified array.
      Parameters:
      array - input array
      length - length to be stored

    • length

      public static int length(byte[] array, int pos)
      Returns the compressed length of the value at the specified position.
      Parameters:
      array - array
      pos - position where the value is found
      Returns:
      value length

    • length

      public static int length(int v)
      Returns the compressed length of the specified value.
      Parameters:
      v - integer value
      Returns:
      value length

    • toString

      public static String toString(byte[] num)
      Returns a string representation of the specified number array.
      Parameters:
      num - numbers
      Returns:
      string