source: downloads/OgreMain/include/OgreBitwise.h @ 3

/*
-----------------------------------------------------------------------------
This source file is part of OGRE
    (Object-oriented Graphics Rendering Engine)
For the latest info, see http://www.ogre3d.org/

Copyright (c) 2000-2006 Torus Knot Software Ltd
Also see acknowledgements in Readme.html

This program is free software; you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License as published by the Free Software
Foundation; either version 2 of the License, or (at your option) any later
version.

This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with
this program; if not, write to the Free Software Foundation, Inc., 59 Temple
Place - Suite 330, Boston, MA 02111-1307, USA, or go to
http://www.gnu.org/copyleft/lesser.txt.

You may alternatively use this source under the terms of a specific version of
the OGRE Unrestricted License provided you have obtained such a license from
Torus Knot Software Ltd.
-----------------------------------------------------------------------------
*/
#ifndef _Bitwise_H__
#define _Bitwise_H__

#include "OgrePrerequisites.h"

namespace Ogre {

    /** Class for manipulating bit patterns.
    */
    class Bitwise {
    public:
        /** Returns the most significant bit set in a value.
        */
        static FORCEINLINE unsigned int mostSignificantBitSet(unsigned int value)
        {
            unsigned int result = 0;
            while (value != 0) {
                ++result;
                value >>= 1;
            }
            return result-1;
        }
        /** Returns the closest power-of-two number greater or equal to value.
            @note 0 and 1 are powers of two, so 
                firstPO2From(0)==0 and firstPO2From(1)==1.
        */
        static FORCEINLINE uint32 firstPO2From(uint32 n)
        {
            --n;            
            n |= n >> 16;
            n |= n >> 8;
            n |= n >> 4;
            n |= n >> 2;
            n |= n >> 1;
            ++n;
            return n;
        }
        /** Determines whether the number is power-of-two or not.
            @note 0 and 1 are tread as power of two.
        */
        template<typename T>
        static FORCEINLINE bool isPO2(T n)
        {
            return (n & (n-1)) == 0;
        }
        /** Returns the number of bits a pattern must be shifted right by to
            remove right-hand zeroes.
        */
                template<typename T>
        static FORCEINLINE unsigned int getBitShift(T mask)
                {
                        if (mask == 0)
                                return 0;

                        unsigned int result = 0;
                        while ((mask & 1) == 0) {
                                ++result;
                                mask >>= 1;
                        }
                        return result;
                }

        /** Takes a value with a given src bit mask, and produces another
            value with a desired bit mask.
            @remarks
                This routine is useful for colour conversion.
        */
                template<typename SrcT, typename DestT>
        static inline DestT convertBitPattern(SrcT srcValue, SrcT srcBitMask, DestT destBitMask)
                {
                        // Mask off irrelevant source value bits (if any)
                        srcValue = srcValue & srcBitMask;

                        // Shift source down to bottom of DWORD
                        const unsigned int srcBitShift = getBitShift(srcBitMask);
                        srcValue >>= srcBitShift;

                        // Get max value possible in source from srcMask
                        const SrcT srcMax = srcBitMask >> srcBitShift;

                        // Get max avaiable in dest
                        const unsigned int destBitShift = getBitShift(destBitMask);
                        const DestT destMax = destBitMask >> destBitShift;

                        // Scale source value into destination, and shift back
                        DestT destValue = (srcValue * destMax) / srcMax;
                        return (destValue << destBitShift);
                }

        /**
         * Convert N bit colour channel value to P bits. It fills P bits with the
         * bit pattern repeated. (this is /((1<<n)-1) in fixed point)
         */
        static inline unsigned int fixedToFixed(uint32 value, unsigned int n, unsigned int p) 
        {
            if(n > p) 
            {
                // Less bits required than available; this is easy
                value >>= n-p;
            } 
            else if(n < p)
            {
                // More bits required than are there, do the fill
                // Use old fashioned division, probably better than a loop
                if(value == 0)
                        value = 0;
                else if(value == (static_cast<unsigned int>(1)<<n)-1)
                        value = (1<<p)-1;
                else    value = value*(1<<p)/((1<<n)-1);
            }
            return value;    
        }

        /**
         * Convert floating point colour channel value between 0.0 and 1.0 (otherwise clamped) 
         * to integer of a certain number of bits. Works for any value of bits between 0 and 31.
         */
        static inline unsigned int floatToFixed(const float value, const unsigned int bits)
        {
            if(value <= 0.0f) return 0;
            else if (value >= 1.0f) return (1<<bits)-1;
            else return (unsigned int)(value * (1<<bits));     
        }

        /**
         * Fixed point to float
         */
        static inline float fixedToFloat(unsigned value, unsigned int bits)
        {
            return (float)value/(float)((1<<bits)-1);
        }

        /**
         * Write a n*8 bits integer value to memory in native endian.
         */
        static inline void intWrite(void *dest, const int n, const unsigned int value)
        {
            switch(n) {
                case 1:
                    ((uint8*)dest)[0] = (uint8)value;
                    break;
                case 2:
                    ((uint16*)dest)[0] = (uint16)value;
                    break;
                case 3:
#if OGRE_ENDIAN == OGRE_ENDIAN_BIG      
                    ((uint8*)dest)[0] = (uint8)((value >> 16) & 0xFF);
                    ((uint8*)dest)[1] = (uint8)((value >> 8) & 0xFF);
                    ((uint8*)dest)[2] = (uint8)(value & 0xFF);
#else
                    ((uint8*)dest)[2] = (uint8)((value >> 16) & 0xFF);
                    ((uint8*)dest)[1] = (uint8)((value >> 8) & 0xFF);
                    ((uint8*)dest)[0] = (uint8)(value & 0xFF);
#endif
                    break;
                case 4:
                    ((uint32*)dest)[0] = (uint32)value;                
                    break;                
            }        
        }
        /**
         * Read a n*8 bits integer value to memory in native endian.
         */
        static inline unsigned int intRead(const void *src, int n) {
            switch(n) {
                case 1:
                    return ((uint8*)src)[0];
                case 2:
                    return ((uint16*)src)[0];
                case 3:
#if OGRE_ENDIAN == OGRE_ENDIAN_BIG      
                    return ((uint32)((uint8*)src)[0]<<16)|
                            ((uint32)((uint8*)src)[1]<<8)|
                            ((uint32)((uint8*)src)[2]);
#else
                    return ((uint32)((uint8*)src)[0])|
                            ((uint32)((uint8*)src)[1]<<8)|
                            ((uint32)((uint8*)src)[2]<<16);
#endif
                case 4:
                    return ((uint32*)src)[0];
            } 
            return 0; // ?
        }

        /** Convert a float32 to a float16 (NV_half_float)
                Courtesy of OpenEXR
        */
        static inline uint16 floatToHalf(float i)
        {
            union { float f; uint32 i; } v;
            v.f = i;
            return floatToHalfI(v.i);
        }
                /** Converts float in uint32 format to a a half in uint16 format
                */
        static inline uint16 floatToHalfI(uint32 i)
        {
            register int s =  (i >> 16) & 0x00008000;
            register int e = ((i >> 23) & 0x000000ff) - (127 - 15);
            register int m =   i        & 0x007fffff;
        
            if (e <= 0)
            {
                if (e < -10)
                {
                    return 0;
                }
                m = (m | 0x00800000) >> (1 - e);
        
                return s | (m >> 13);
            }
            else if (e == 0xff - (127 - 15))
            {
                if (m == 0) // Inf
                {
                    return s | 0x7c00;
                } 
                else    // NAN
                {
                    m >>= 13;
                    return s | 0x7c00 | m | (m == 0);
                }
            }
            else
            {
                if (e > 30) // Overflow
                {
                    return s | 0x7c00;
                }
        
                return s | (e << 10) | (m >> 13);
            }
        }
        
        /**
         * Convert a float16 (NV_half_float) to a float32
         * Courtesy of OpenEXR
         */
        static inline float halfToFloat(uint16 y)
        {
            union { float f; uint32 i; } v;
            v.i = halfToFloatI(y);
            return v.f;
        }
                /** Converts a half in uint16 format to a float
                        in uint32 format
                 */
        static inline uint32 halfToFloatI(uint16 y)
        {
            register int s = (y >> 15) & 0x00000001;
            register int e = (y >> 10) & 0x0000001f;
            register int m =  y        & 0x000003ff;
        
            if (e == 0)
            {
                if (m == 0) // Plus or minus zero
                {
                    return s << 31;
                }
                else // Denormalized number -- renormalize it
                {
                    while (!(m & 0x00000400))
                    {
                        m <<= 1;
                        e -=  1;
                    }
        
                    e += 1;
                    m &= ~0x00000400;
                }
            }
            else if (e == 31)
            {
                if (m == 0) // Inf
                {
                    return (s << 31) | 0x7f800000;
                }
                else // NaN
                {
                    return (s << 31) | 0x7f800000 | (m << 13);
                }
            }
        
            e = e + (127 - 15);
            m = m << 13;
        
            return (s << 31) | (e << 23) | m;
        }
         

    };
}

#endif