Bit field class

phaana (Irfan Hamid) — Thu, 15 May 2008 11:48:59 GMT

// A bit field is an important data structure in computer science, major uses include memory allocators and Bloom filters.
// The code is in the form of a header file and an implementation file.





// This class is a code snippet, it can be freely used and distributed.

// Author: irfan[dot]hamid[at]gmail[dot]com

//

// Bit fields are a widely used mechanism in computing applications.

// Typical applications include memory allocators and Bloom filters. This class

// provides a generic bit field implementation for an arbitrary number of bits.

//

// Implementation notes:

// The use of C++ allows the clean separation of the data structure from the

// interface. The bit field is implemented as a vector of unsigned int that is

// allocated at object creation.

//

// field: The vector that represents the bit field itself

// bit_count: The total number of bits in the bit field



#ifndef __BITFIELD_H__

#define __BITFIELD_H__

#include 

#define SZ_UINT sizeof(unsigned int)



class Bitfield

{

protected:

	unsigned int *field;

	unsigned int bit_count;



public:

	Bitfield (int bc);

	~Bitfield ();



	int set (int bit);

	int get (int bit);

	int reset (int bit);

};



#endif







#include 

#include "bitfield.h"



// The constructor takes an int param which gives the number of bits in this

// bit field.

Bitfield::Bitfield (int bc)

{

	bit_count = bc;



	// E.g, ceil(257/32*8) = 65, 64 ints fully used, last one partially used

	field = (unsigned int*) malloc(((int) ceil(bc/SZ_UINT*8)));

}



Bitfield::~Bitfield ()

{

	if (field)

		free(field);

}



// This function sets the corresponding bit in the field equal to 1.

//

// Returns: 0 on success, -1 on error.

int Bitfield::set (int bit)

{

	// Sanity check

	if (bit >= bit_count || !field)

		return -1;



	// The correct index into the vector will be given by bit/SZ_UNIT. The

	// index into the correct vector element is given by bit%SZ_UNIT, to

	// achieve this, simply left shift 0x01 the appropriate number of times.

	field[bit/SZ_UINT] |= (0x00000001 << (bit%(SZ_UINT*8)-1));

	return 0;

}



// This function sets the corresponding bit in the field equal to 0.

//

// Returns: 0 on success, -1 on error.

int Bitfield::reset (int bit)

{

	if (bit >= bit_count || !field)

		return -1;

	field[bit/SZ_UINT] &= ~(0x00000001 << (bit%(SZ_UINT*8)-1));

	return 0;

}



// This function returns the value of the corresponding bit.

//

// Returns: The value of the bit, if the field is initialized and bit index is

// within bounds, -1 otherwise.

int Bitfield::get (int bit)

{

	if (bit >= bit_count || !field)

		return -1;

	return (field[bit/SZ_UINT] & (0x00000001 << (bit%(SZ_UINT*8)-1)) ? 1 : 0);

}

Bitwise Operation: Quickly Convert Binary Bit to Integer and vice versa using Javascript Shell

agilekai (kai) — Wed, 07 Nov 2007 05:56:13 GMT

using JavaScript shell found at www.squarefree.com/shell/ , it's very easy to convert binary bit to integer and vice versa

convert integer to binary bit string



num = 1024

num.toString(2)

convert binary bit string to integer



parseInt('111', 2)

Count number of set bits in an integer

peter (Peter Cooperx) — Mon, 02 Jul 2007 01:12:15 GMT



count = 0

count += byte & 1 and byte >>= 1 until byte == 0

DZone Snippets: bitwise code

Bit field class

Bitwise Operation: Quickly Convert Binary Bit to Integer and vice versa using Javascript Shell

Count number of set bits in an integer