Multiply32.hh

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#ifndef MULTIPLY32_HH
#define MULTIPLY32_HH
 
#include <array>
#include <bit>
#include <concepts>
#include <cstdint>
 
namespace openmsx {
 
template<std::unsigned_integral Pixel> class PixelOperations;
 
template<std::unsigned_integral Pixel> class Multiply32;
 
template<> class Multiply32<uint32_t>
{
public:
        explicit Multiply32(const PixelOperations<uint32_t>& /*format*/) {
                // nothing
        }
 
        inline void setFactor32(unsigned f)
        {
                factor = f;
        }
 
        [[nodiscard]] inline uint32_t mul32(uint32_t p) const
        {
                return ((((p       & 0x00FF00FF) * factor) & 0xFF00FF00) >> 8)
                     | ((((p >> 8) & 0x00FF00FF) * factor) & 0xFF00FF00);
        }
 
        [[nodiscard]] inline uint32_t conv32(uint32_t p) const
        {
                return p;
        }
 
private:
        unsigned factor = 0;
};
 
template<> class Multiply32<uint16_t>
{
public:
        explicit Multiply32(const PixelOperations<uint16_t>& pixelOps);
 
        void setFactor32(unsigned factor);
 
        [[nodiscard]] inline uint32_t mul32(uint16_t p) const
        {
                return tab[p];
        }
 
        [[nodiscard]] inline uint16_t conv32(uint32_t p) const
        {
                return uint16_t(
                        (std::rotr(p, Rshift3) & Rmask1) |
                        (std::rotr(p, Gshift3) & Gmask1) |
                        (std::rotr(p, Bshift3) & Bmask1));
        }
 
private:
        std::array<uint32_t, 0x10000> tab = {}; // fill with zero
        unsigned factor = 0;
        int Rshift1, Gshift1, Bshift1;
        int Rshift2, Gshift2, Bshift2;
        int Rshift3, Gshift3, Bshift3;
        uint16_t Rmask1, Gmask1, Bmask1;
        uint16_t Rmask2, Gmask2, Bmask2;
};
 
} // namespace openmsx
 
#endif