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/* ----------------------------------------------------------------------- *
 * This file is part of GEL, http://www.imm.dtu.dk/GEL
 * Copyright (C) the authors and DTU Informatics
 * For license and list of authors, see ../../doc/intro.pdf
 * ----------------------------------------------------------------------- */

/** @file BitMask.h
 * @brief BitMask class for selecting bit subsets ... possibly a bit dusty
 */

#ifndef __CGLA__BITMASK_H__
#define __CGLA__BITMASK_H__

#include "Vec3i.h"

namespace CGLA
{
        const int MASKS[33] = 
                {
                        0x00000000,
                        0x00000001,
                        0x00000003,
                        0x00000007,
                        0x0000000f,
                        0x0000001f,
                        0x0000003f,
                        0x0000007f,
                        0x000000ff,
                        0x000001ff,
                        0x000003ff,
                        0x000007ff,
                        0x00000fff,
                        0x00001fff,
                        0x00003fff,
                        0x00007fff,
                        0x0000ffff,
                        0x0001ffff,
                        0x0003ffff,
                        0x0007ffff,
                        0x000fffff,
                        0x001fffff,
                        0x003fffff,
                        0x007fffff,
                        0x00ffffff,
                        0x01ffffff,
                        0x03ffffff,
                        0x07ffffff,
                        0x0fffffff,
                        0x1fffffff,
                        0x3fffffff,
                        0x7fffffff,
                        static_cast<int>(0xffffffff)
                };

        /** \brief The BitMask class is mostly a utility class.

                        The main purpose is to be able to extract a set of bits from
                        an integer. For instance this can be useful if we traverse
                        some tree structure and the integer is the index. */
        class BitMask
        {
                int fb, lb, bdiff;
                int msk;

        public:

                /** Mask _fb-_lb+1 bits beginning from _fb. First bit is 0.
                                Say _fb=_lb=0. In this case, mask 1 bit namely 0.*/
                BitMask(int _fb, int _lb):
                        fb(_fb), lb(_lb), 
                        bdiff(lb-fb+1), msk(MASKS[bdiff]<<fb)
                {}
        
                /// first bit is 0 mask num bits.
                BitMask(int num):
                        fb(0),lb(two_to_what_power(num)-1), 
                        bdiff(lb-fb+1), msk(MASKS[bdiff]<<fb)
                {}
        
                /// Mask everything.
                BitMask():
                        fb(0), lb(15),
                        bdiff(lb-fb+1), msk(MASKS[bdiff]<<fb)
                {}

                /// get number of first bit in mask
                int first_bit() const {return fb;} 

                /// get number of last bit in mask
                int last_bit() const {return lb;}

                /// Return number of masked bits
                int no_bits() const {return bdiff;}

                /// Mask a number
                int mask(int var) const {return msk&var;}
                
                /** Mask a number and shift back so the first bit inside
                                the mask becomes bit 0. */
                int mask_shift(int var) const {return (msk&var)>>fb;}

                /** Mask a vector by masking each coordinate. */
                Vec3i mask(const Vec3i& v) const 
                {
                        return Vec3i(mask(v[0]),mask(v[1]),mask(v[2]));
                }
  
                /** Mask each coord of a vector and shift */
                Vec3i maskshift(const Vec3i& v) const 
                {
                        return Vec3i(mask_shift(v[0]),mask_shift(v[1]),mask_shift(v[2]));
                }
  
        };

}
#endif