C:/knet/include/kNet/BitOps.h

Go to the documentation of this file.

/* Copyright 2010 Jukka Jylänki

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License. */
#pragma once

#include <cassert>

#include "Types.h"

namespace kNet
{

u32 BinaryStringToValue(const char *str);

inline int CountBitsSet(u32 value)
{
   int bits = 0;
   while(value)
   {
      value &= value - 1;
      ++bits;
   }
   return bits;
}

// Clears the LSB bit and returns the zero-based index of where the bit was set.
inline int ExtractLSB(unsigned long *value)
{
   for(int i = 0; i < 32; ++i)
      if ((*value & (1 << i)) != 0)
      {
         *value &= ~(1 << i);
         return i;
      }
   return -1;
}

template<int Bits>
class LSBT
{
public:
   enum { val = (1 << Bits) - 1 };
};


template<>
class LSBT<32>
{
public:
   enum { val = 0xFFFFFFFF };
};

template<>
class LSBT<31>
{
public:
   enum { val = 0x7FFFFFFF };
};


inline u32 LSB(u32 bits)
{
   assert(bits <= 32);
   if (bits >= 32)
      return 0xFFFFFFFF;
   return (1 << bits) - 1;
}

template<int Pos, int Bits>
class BitMaskT
{
public:
// enum { val = (Pow<2, Bits>::val - 1) << Pos };        // Alternate way to calculate this value.
   enum { val = LSBT<Pos+Bits>::val & ~LSBT<Pos>::val }; // But this is nicer.
};

inline u32 BitMask(u32 pos, u32 bits)
{
   return LSB(pos + bits) & ~LSB(pos);
}

template<typename ResultType, typename InputType,
         int APos, int ABits, int RPos, int RBits,
         int GPos, int GBits, int BPos, int BBits>
ResultType PackBits(InputType a, InputType r, InputType g, InputType b)
{
   return (ResultType)(
      (ResultType)a << APos & BitMaskT<APos, ABits>::val | 
      (ResultType)r << RPos & BitMaskT<RPos, RBits>::val |
      (ResultType)g << GPos & BitMaskT<GPos, GBits>::val |
      (ResultType)b << BPos & BitMaskT<BPos, BBits>::val);
}

template<typename ResultType, typename InputType>
ResultType PackBits(int APos, int ABits, int RPos, int RBits, 
                             int GPos, int GBits, int BPos, int BBits, 
                             InputType a, InputType r, InputType g, InputType b)
{
   return (ResultType)(
      (ResultType)a << APos & BitMask(APos, ABits) | 
      (ResultType)r << RPos & BitMask(RPos, RBits) |
      (ResultType)g << GPos & BitMask(GPos, GBits) |
      (ResultType)b << BPos & BitMask(BPos, BBits));
}

template<typename ResultType, typename InputType, int Pos, int Bits>
void ExtractBits(ResultType &out, const InputType &in)
{
   out = (ResultType)(in >> Pos & BitMaskT<0, Bits>::val);
}

template<typename ResultType, typename InputType>
void ExtractBits(int pos, int bits, ResultType &out, const InputType &in)
{
   out = (ResultType)(in >> pos & BitMask(0, bits));
}

} // ~kNet