cern.colt.matrix.tbit

Class QuickBitVector

java.lang.Object

cern.colt.matrix.tbit.QuickBitVector

public class QuickBitVector
extends java.lang.Object

Implements quick non polymorphic non bounds checking low level bitvector operations. Includes some operations that interpret sub-bitstrings as long integers.

WARNING: Methods of this class do not check preconditions. Provided with invalid parameters these method may return (or set) invalid values without throwing any exception. You should only use this class when performance is critical and you are absolutely sure that indexes are within bounds.

A bitvector is modelled as a long array, i.e. long[] bits holds bits of a bitvector. Each long value holds 64 bits. The i-th bit is stored in bits[i/64] at bit position i % 64 (where bit position 0 refers to the least significant bit and 63 refers to the most significant bit).

See Also:

BitVector, BitMatrix, BitSet

Method Summary

Modifier and Type	Method and Description
static long	bitMaskWithBitsSetFromTo(int from, int to) Returns a bit mask with bits in the specified range set to 1, all the rest set to 0.
static void	clear(long[] bits, int bitIndex) Changes the bit with index bitIndex in the bitvector bits to the "clear" (false) state.
static boolean	get(long[] bits, int bitIndex) Returns from the bitvector the value of the bit with the specified index.
static long	getLongFromTo(long[] bits, int from, int to) Returns a long value representing bits of a bitvector from index from to index to.
static int	leastSignificantBit(int value) Returns the index of the least significant bit in state "true".
static long[]	makeBitVector(int size, int bitsPerElement) Constructs a low level bitvector that holds size elements, with each element taking bitsPerElement bits.
static int	mostSignificantBit(int value) Returns the index of the most significant bit in state "true".
static void	put(long[] bits, int bitIndex, boolean value) Sets the bit with index bitIndex in the bitvector bits to the state specified by value.
static void	putLongFromTo(long[] bits, long value, int from, int to) Sets bits of a bitvector from index from to index to to the bits of value.
static void	set(long[] bits, int bitIndex) Changes the bit with index bitIndex in the bitvector bits to the "set" (true) state.

Methods inherited from class java.lang.Object

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

Method Detail

bitMaskWithBitsSetFromTo

public static final long bitMaskWithBitsSetFromTo(int from,
                                                  int to)

Returns a bit mask with bits in the specified range set to 1, all the rest set to 0. In other words, returns a bit mask having 0,1,2,3,...,64 bits set. If to-from+1==0 then returns zero (0L). Precondition (not checked): to-from+1 >= 0 && to-from+1 <= 64.

Parameters:

from - index of start bit (inclusive)

to - index of end bit (inclusive).

Returns:

the bit mask having all bits between from and to set to 1.

clear

public static void clear(long[] bits,
                         int bitIndex)

Changes the bit with index bitIndex in the bitvector bits to the "clear" (false) state.

Parameters:

bits - the bitvector.

bitIndex - the index of the bit to be cleared.

get

public static boolean get(long[] bits,
                          int bitIndex)

Returns from the bitvector the value of the bit with the specified index. The value is true if the bit with the index bitIndex is currently set; otherwise, returns false.

Parameters:

bits - the bitvector.

bitIndex - the bit index.

Returns:

the value of the bit with the specified index.

getLongFromTo

public static long getLongFromTo(long[] bits,
                                 int from,
                                 int to)

Returns a long value representing bits of a bitvector from index from to index to. Bits are returned as a long value with the return value having bit 0 set to bit from, ..., bit to-from set to bit to. All other bits of return value are set to 0. If from > to then returns zero ( 0L). Precondition (not checked): to-from+1 <= 64.

Parameters:

bits - the bitvector.

from - index of start bit (inclusive).

to - index of end bit (inclusive).

Returns:

the specified bits as long value.

leastSignificantBit

public static int leastSignificantBit(int value)

Returns the index of the least significant bit in state "true". Returns 32 if no bit is in state "true". Examples:

         0x80000000 --> 31
         0x7fffffff --> 0
         0x00000001 --> 0
         0x00000000 --> 32
 
 

makeBitVector

public static long[] makeBitVector(int size,
                                   int bitsPerElement)

Constructs a low level bitvector that holds size elements, with each element taking bitsPerElement bits.

Parameters:

size - the number of elements to be stored in the bitvector (must be >= 0).

bitsPerElement - the number of bits one single element takes.

Returns:

a low level bitvector.

mostSignificantBit

public static int mostSignificantBit(int value)

Returns the index of the most significant bit in state "true". Returns -1 if no bit is in state "true". Examples:

         0x80000000 --> 31
         0x7fffffff --> 30
         0x00000001 --> 0
         0x00000000 --> -1
 
 

put

public static void put(long[] bits,
                       int bitIndex,
                       boolean value)

Sets the bit with index bitIndex in the bitvector bits to the state specified by value.

Parameters:

bits - the bitvector.

bitIndex - the index of the bit to be changed.

value - the value to be stored in the bit.

putLongFromTo

public static void putLongFromTo(long[] bits,
                                 long value,
                                 int from,
                                 int to)

Sets bits of a bitvector from index from to index to to the bits of value. Bit from is set to bit 0 of value, ..., bit to is set to bit to-from of value. All other bits stay unaffected. If from > to then does nothing. Precondition (not checked): to-from+1 <= 64.

Parameters:

bits - the bitvector.

value - the value to be copied into the bitvector.

from - index of start bit (inclusive).

to - index of end bit (inclusive).

set

public static void set(long[] bits,
                       int bitIndex)

Changes the bit with index bitIndex in the bitvector bits to the "set" (true) state.

Parameters:

bits - the bitvector.

bitIndex - the index of the bit to be set.