template and bit-field

[mathieu]

Hello,

I am trying to use template programing and bit-field and I came up
with (*). I was not able to make a really clean solution but instead
separate into 3 cases:
1. mask is declare before the value
2. value is declare before the mask
3. for zero bit field mask need to be unnamed

Is there another solution that would have been cleaner (less
specific cases) ?

Thanks
-Mathieu

(*)
/*
Bits Allocated = 16
Bits Stored = 12
High Bit = 11

|<------------------ pixel -----------------

>|

______________ ______________ ______________
______________
|XXXXXXXXXXXXXX | | |
|
|______________ |______________ |______________ |
______________|
15 12 11 8 7 4 3
0

---------------------------

Bits Allocated = 16
Bits Stored = 12
High Bit = 15

|<------------------ pixel ----------------->|
______________ ______________ ______________
______________
| | | |
XXXXXXXXXXXXXX|
|______________ |______________ |______________ |
______________|
15 12 11 8 7 4 3
0

---------------------------

Bits Allocated = 12
Bits Stored = 12
High Bit = 11

------ 2 ----->|<------------------ pixel 1 ---------------

>|

______________ ______________ ______________
______________
| | | |
|
|______________ |______________ |______________ |
______________|
15 12 11 8 7 4 3
0
-------------- 3 ------------>|<------------ 2
--------------
______________ ______________ ______________
______________
| | | |
|
|______________ |______________ |______________ |
______________|
15 12 11 8 7 4 3
0
|<------------------ pixel 4 --------------->|<----- 3
------
______________ ______________ ______________
______________
| | | |
|
|______________ |______________ |______________ |
______________|
15 12 11 8 7 4 3
0
*/

#include <iostream>

template <intstruct BitsAllocatedTo Type;
template<struct BitsAllocatedTo Type<16{ typedef unsigned short
Type; };
template<struct BitsAllocatedTo Type<12{ typedef unsigned short
Type; };
template<struct BitsAllocatedTo Type<8{ typedef unsigned char
Type; };

template <int BitsAllocated, int BitsStored, int typestruct
PixelDetail;
// mask last:
template<int BitsAllocated, int BitsStored>
struct PixelDetail<Bit sAllocated, BitsStored, 1>
{
typedef typename BitsAllocatedTo Type<BitsAlloca ted>::Type Type;
public:
Type v:BitsStored;
private:
Type mask:(BitsAlloc ated-BitsStored);
};
// mask first:
template<int BitsAllocated, int BitsStored>
struct PixelDetail<Bit sAllocated, BitsStored, -1>
{
typedef typename BitsAllocatedTo Type<BitsAlloca ted>::Type Type;
private:
Type mask:(BitsAlloc ated-BitsStored);
public:
Type v:BitsStored;
};
// unamed zero bit-field:
template<int BitsAllocated, int BitsStored>
struct PixelDetail<Bit sAllocated, BitsStored, 0>
{
// static_assert( BitsAllocated == BitsStored )
typedef typename BitsAllocatedTo Type<BitsAlloca ted>::Type Type;
private:
Type :(BitsAllocated-BitsStored);
public:
Type v:BitsStored;
};
// Bits Allocated
// Bits Stored
// High Bit
template <int BitsAllocated, int BitsStored, int HighBits>
struct Pixel : public PixelDetail<Bit sAllocated, BitsStored,
(BitsAllocated - BitsStored) ? ((BitsStored < HighBits) ? 1 : -1) : 0>
{
typedef typename BitsAllocatedTo Type<BitsAlloca ted>::Type Type;
operator Type () const { return this->v; }
};

int main()
{
Pixel<16,12,15p ixel1;
Pixel<16,12,11p ixel2;
Pixel<12,12,11p ixel3;
Pixel<16,16,15p ixel4;

const unsigned short v = 0xcdef;
memcpy(&pixel1, &v,sizeof(unsig ned short));
memcpy(&pixel2, &v,sizeof(unsig ned short));
memcpy(&pixel3, &v,sizeof(unsig ned short));
memcpy(&pixel4, &v,sizeof(unsig ned short));

std::cout << std::hex << pixel1 << std::endl;
std::cout << std::hex << pixel2 << std::endl;
std::cout << std::hex << pixel3 << std::endl;
std::cout << std::hex << pixel4 << std::endl;

return 0;
}