Class FormatableBitSet

java.lang.Object
org.apache.derby.iapi.services.io.FormatableBitSet
All Implemented Interfaces:
Externalizable, Serializable, Cloneable, Formatable, TypedFormat

public final class FormatableBitSet extends Object implements Formatable, Cloneable
FormatableBitSet is implemented as a packed array of bytes.
See Also:
  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    private byte
     
    private int
     
    private byte[]
    Bits are stored as an array of bytes.
  • Constructor Summary

    Constructors
    Constructor
    Description
    Niladic Constructor
    FormatableBitSet(byte[] newValue)
    Constructs a Bit from an array of bytes.
    FormatableBitSet(int numBits)
    Constructs a Bit with the initial number of bits
    Copy constructor
  • Method Summary

    Modifier and Type
    Method
    Description
    void
    Bitwise AND this FormatableBitSet with another FormatableBitSet.
    int
    If any bit is set, return the zero-based bit index of the first bit that is set.
    int
    anySetBit(int beyondBit)
    Like anySetBit(), but return any set bit whose number is bigger than beyondBit.
    private int
    calculateLength(int realByteLength)
     
    private final void
     
    void
    Clear all the bits in this FormatableBitSet
    void
    clear(int position)
    Bit clear
     
    int
    Bit comparison.
    void
    Copy the bytes from another FormatableBitSet.
    boolean
    equals(Object other)
    Bit equivalence.
    private static byte
    firstSet(byte v)
    A utility method which treats the byte argument as an 8-bit bitset and finds the first set bit in that byte.
    final boolean
    get(int position)
    Bit get -- alias for isSet()
    byte[]
    Get the value of the byte array
    int
    Get the length in bits
    int
    Get the length in bytes of a Bit value
    int
    Get a count of the number of bits that are set.
    int
    Get the formatID which corresponds to this class.
    void
    grow(int n)
    Grow (widen) a FormatableBitSet so that it contains at least N bits.
    int
    Produce a hash code by putting the value bytes into an int, exclusive OR'ing if there are more than 4 bytes.
    private void
    initializeBits(int numBits)
     
    boolean
    This method returns true if the following conditions hold: 1.
    final boolean
    isSet(int position)
    Bit isSet
    static int
    maxBitsForSpace(int numBytes)
    Statically calculates how many bits can fit into the number of bytes if this Bit object is externalized.
    private static byte
    Figure out how many bits are in the last byte from the total number of bits.
    private static int
    numBytesFromBits(int bits)
    Figure out how many bytes are needed to store the input number of bits.
    void
    or(FormatableBitSet otherBit)
    Bitwise OR this FormatableBitSet with another FormatableBitSet.
    void
    Note: gracefully handles zero length bits -- will create a zero length array with no bits being used.
    void
    set(int position)
    Bit set
    void
    shrink(int n)
    Shrink (narrow) a FormatableBitSet to N bits.
    int
    Get the length in bits -- alias for getLength()
    Format the string into BitSet format: {0, 2, 4, 8} if bits 0, 2, 4, 8 are set.
    private static int
    udiv8(int i)
     
    private static byte
    umod8(int i)
     
    private static int
    umul8(int i)
     
    void
    Format: int length in bits byte[]
    void
    Bitwise XOR this FormatableBitSet with another FormatableBitSet.

    Methods inherited from class java.lang.Object

    finalize, getClass, notify, notifyAll, wait, wait, wait
  • Field Details

    • value

      private byte[] value
      Bits are stored as an array of bytes. Bits are numbered starting at 0. Bits 0..7 go in byte[0], 8..15 in byte[1] and so on. The number of bytes is tracked as part of the byte array. The number of bits being used is derived by the number of bytes being used and the number of bits being used by the last byte. The partially unused byte is always byte[byte.length] with the lowest bits being unused. Zero length bits are stored using a zero length byte array, with all bits marked as unused.
    • bitsInLastByte

      private byte bitsInLastByte
    • lengthAsBits

      private transient int lengthAsBits
  • Constructor Details

    • FormatableBitSet

      public FormatableBitSet()
      Niladic Constructor
    • FormatableBitSet

      public FormatableBitSet(int numBits)
      Constructs a Bit with the initial number of bits
    • FormatableBitSet

      public FormatableBitSet(byte[] newValue)
      Constructs a Bit from an array of bytes. Assume bytes are all being used.
      Parameters:
      newValue - The array of bytes to make up the new Bit
    • FormatableBitSet

      public FormatableBitSet(FormatableBitSet original)
      Copy constructor
      Parameters:
      original - the FormatableBitSet to make a copy from
  • Method Details

    • checkPosition

      private final void checkPosition(int p)
    • udiv8

      private static int udiv8(int i)
    • umod8

      private static byte umod8(int i)
    • umul8

      private static int umul8(int i)
    • initializeBits

      private void initializeBits(int numBits)
    • clone

      public Object clone()
      Overrides:
      clone in class Object
    • invariantHolds

      public boolean invariantHolds()
      This method returns true if the following conditions hold: 1. The number of bits in the bitset will fit into the allocated byte array. 2. 'lengthAsBits' and 'bitsInLastByte' are consistent. 3. All unused bits in the byte array are unset. This represents an invariant for the class, so this method should always return true. The method is public, but is primarily intended for testing and ASSERTS.
      Returns:
      true if invariant holds, false otherwise
    • getLengthInBytes

      public int getLengthInBytes()
      Get the length in bytes of a Bit value
      Returns:
      The length in bytes of this value
    • getLength

      public int getLength()
      Get the length in bits
      Returns:
      The length in bits for this value NOTE: could possibly be changed to a long. As is we are restricted to 2^(31-3) -> 256meg instead of 2^31 (Integer.MAX_VALUE) like other datatypes (or 2 gig). If it is ever changed to a long be sure to change read/writeExternal which write out the length in bits.
    • calculateLength

      private int calculateLength(int realByteLength)
    • size

      public int size()
      Get the length in bits -- alias for getLength()
      Returns:
      The length in bits for this value
    • getByteArray

      public byte[] getByteArray()
      Get the value of the byte array
      Returns:
      The value of the byte array
    • grow

      public void grow(int n)
      Grow (widen) a FormatableBitSet so that it contains at least N bits. If the bitset already has more than n bits, this is a noop. Negative values of n are not allowed. ASSUMPTIONS: that all extra bits in the last byte are zero.
      Parameters:
      n - The number of bits you want. The bits are always added as 0 and are appended to the least significant end of the bit array.
    • shrink

      public void shrink(int n)
      Shrink (narrow) a FormatableBitSet to N bits. N may not be larger than the current bitset size, or negative.
      Parameters:
      n - The number of bits the caller wants. The bits are always removed from the least significant end of the bit array.
    • equals

      public boolean equals(Object other)
      Bit equivalence. Compare this with other. If the length is different, then cannot be equal so short circuit. Otherwise, rely on compare(). Note that two zero length bits are considered equal.
      Overrides:
      equals in class Object
      Parameters:
      other - the other bit to compare to
      Returns:
      TRUE|FALSE
    • compare

      public int compare(FormatableBitSet other)
      Bit comparison. Compare this with other. Will always do a byte by byte compare. Given 2 similar bits of unequal lengths (x and y), where x.getLength() < y.getLength() but where: x[0..x.getLength()] == y[0..x.getLength()] then x < y.
      Parameters:
      other - the other bit to compare to
      Returns:
      -1 - if other < this 0 - if other == this 1 - if other > this
    • hashCode

      public int hashCode()
      Produce a hash code by putting the value bytes into an int, exclusive OR'ing if there are more than 4 bytes.
      Overrides:
      hashCode in class Object
      Returns:
      the hash code
    • isSet

      public final boolean isSet(int position)
      Bit isSet
      Parameters:
      position - the bit to check
    • get

      public final boolean get(int position)
      Bit get -- alias for isSet()
      Parameters:
      position - the bit to check
    • set

      public void set(int position)
      Bit set
      Parameters:
      position - the bit to set
    • clear

      public void clear(int position)
      Bit clear
      Parameters:
      position - the bit to clear
    • clear

      public void clear()
      Clear all the bits in this FormatableBitSet
    • numBytesFromBits

      private static int numBytesFromBits(int bits)
      Figure out how many bytes are needed to store the input number of bits.
      Parameters:
      bits - bits
      Returns:
      the number of bytes
    • numBitsInLastByte

      private static byte numBitsInLastByte(int bits)
      Figure out how many bits are in the last byte from the total number of bits.
      Parameters:
      bits - bits
      Returns:
      the number of bits
    • toString

      public String toString()
      Format the string into BitSet format: {0, 2, 4, 8} if bits 0, 2, 4, 8 are set.
      Overrides:
      toString in class Object
      Returns:
      A new String containing the formatted Bit value
    • maxBitsForSpace

      public static int maxBitsForSpace(int numBytes)
      Statically calculates how many bits can fit into the number of bytes if this Bit object is externalized. Only valid for this implementation of Bit.
    • firstSet

      private static byte firstSet(byte v)
      A utility method which treats the byte argument as an 8-bit bitset and finds the first set bit in that byte. Assumes that at least one bit in v is set (v!=0).
      Parameters:
      v - a non-zero byte to check for set bits
      Returns:
      the zero-based index of the first set bit in the argument byte
    • anySetBit

      public int anySetBit()
      If any bit is set, return the zero-based bit index of the first bit that is set. If no bit is set, return -1. By using anySetBit() and anySetBit(beyondBit), one can quickly go thru the entire bit array to return all set bit.
      Returns:
      the zero-based index of the first bit that is set, or -1 if no bit is set
    • anySetBit

      public int anySetBit(int beyondBit)
      Like anySetBit(), but return any set bit whose number is bigger than beyondBit. If no bit is set after beyondBit, -1 is returned. By using anySetBit() and anySetBit(beyondBit), one can quickly go thru the entire bit array to return all set bit.
      Parameters:
      beyondBit - Only look at bit that is greater than this bit number. Supplying a value of -1 makes the call equivalent to anySetBit().
      Returns:
      the bit number of a bit that is set, or -1 if no bit after beyondBit is set
    • or

      public void or(FormatableBitSet otherBit)
      Bitwise OR this FormatableBitSet with another FormatableBitSet. The result is stored in this bitset. The operand is unaffected. A null operand is treated as an empty bitset (i.e. a noop). A bitset that is smaller than its operand is expanded to the same size.
      Parameters:
      otherBit - bitset operand
    • copyFrom

      public void copyFrom(FormatableBitSet that)
      Copy the bytes from another FormatableBitSet. Assumes that this bit set is at least as large as the argument's bit set.
    • and

      public void and(FormatableBitSet otherBit)
      Bitwise AND this FormatableBitSet with another FormatableBitSet. The result is stored in this bitset. The operand is unaffected. A null operand is treated as an empty bitset (i.e. clearing this bitset). A bitset that is smaller than its operand is expanded to the same size.
      Parameters:
      otherBit - bitset operand
    • xor

      public void xor(FormatableBitSet otherBit)
      Bitwise XOR this FormatableBitSet with another FormatableBitSet. The result is stored in this bitset. The operand is unaffected. A null operand is treated as an empty bitset (i.e. a noop). A bitset that is smaller than its operand is expanded to the same size.
      Parameters:
      otherBit - bitset operand
    • getNumBitsSet

      public int getNumBitsSet()
      Get a count of the number of bits that are set.
      Returns:
      The number of bits that are set.
    • writeExternal

      public void writeExternal(ObjectOutput out) throws IOException
      Format:
      • int length in bits
      • byte[]
      Specified by:
      writeExternal in interface Externalizable
      Throws:
      IOException
      See Also:
    • readExternal

      public void readExternal(ObjectInput in) throws IOException
      Note: gracefully handles zero length bits -- will create a zero length array with no bits being used. Fortunately in.read() is ok with a zero length array so no special code.

      WARNING: this method cannot be changed w/o changing SQLBit because SQLBit calls this directly w/o calling read/writeObject(), so the format id is not stored in that case.

      Specified by:
      readExternal in interface Externalizable
      Throws:
      IOException
      See Also:
    • getTypeFormatId

      public int getTypeFormatId()
      Get the formatID which corresponds to this class.
      Specified by:
      getTypeFormatId in interface TypedFormat
      Returns:
      the formatID of this class