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#if !defined CUDA_DISABLER

#include "opencv2/gpu/device/common.hpp"
#include "opencv2/gpu/device/functional.hpp"
#include "opencv2/gpu/device/emulation.hpp"
#include "opencv2/gpu/device/transform.hpp"

using namespace cv::gpu;
using namespace cv::gpu::device;

namespace hist
{
    __global__ void histogram256Kernel(const uchar* src, int cols, int rows, size_t step, int* hist)
    {
        __shared__ int shist[256];

        const int y = blockIdx.x * blockDim.y + threadIdx.y;
        const int tid = threadIdx.y * blockDim.x + threadIdx.x;

        shist[tid] = 0;
        __syncthreads();

        if (y < rows)
        {
            const unsigned int* rowPtr = (const unsigned int*) (src + y * step);

            const int cols_4 = cols / 4;
            for (int x = threadIdx.x; x < cols_4; x += blockDim.x)
            {
                unsigned int data = rowPtr[x];

                Emulation::smem::atomicAdd(&shist[(data >>  0) & 0xFFU], 1);
                Emulation::smem::atomicAdd(&shist[(data >>  8) & 0xFFU], 1);
                Emulation::smem::atomicAdd(&shist[(data >> 16) & 0xFFU], 1);
                Emulation::smem::atomicAdd(&shist[(data >> 24) & 0xFFU], 1);
            }

            if (cols % 4 != 0 && threadIdx.x == 0)
            {
                for (int x = cols_4 * 4; x < cols; ++x)
                {
                    unsigned int data = ((const uchar*)rowPtr)[x];
                    Emulation::smem::atomicAdd(&shist[data], 1);
                }
            }
        }

        __syncthreads();

        const int histVal = shist[tid];
        if (histVal > 0)
            ::atomicAdd(hist + tid, histVal);
    }

    void histogram256(PtrStepSzb src, int* hist, cudaStream_t stream)
    {
        const dim3 block(32, 8);
        const dim3 grid(divUp(src.rows, block.y));

        histogram256Kernel<<<grid, block, 0, stream>>>(src.data, src.cols, src.rows, src.step, hist);
        cudaSafeCall( cudaGetLastError() );

        if (stream == 0)
            cudaSafeCall( cudaDeviceSynchronize() );
    }
}

/////////////////////////////////////////////////////////////////////////

namespace hist
{
    __constant__ int c_lut[256];

    struct EqualizeHist : unary_function<uchar, uchar>
    {
        float scale;

        __host__ EqualizeHist(float _scale) : scale(_scale) {}

        __device__ __forceinline__ uchar operator ()(uchar val) const
        {
            const int lut = c_lut[val];
            return __float2int_rn(scale * lut);
        }
    };
}

namespace cv { namespace gpu { namespace device
{
    template <> struct TransformFunctorTraits<hist::EqualizeHist> : DefaultTransformFunctorTraits<hist::EqualizeHist>
    {
        enum { smart_shift = 4 };
    };
}}}

namespace hist
{
    void equalizeHist(PtrStepSzb src, PtrStepSzb dst, const int* lut, cudaStream_t stream)
    {
        if (stream == 0)
            cudaSafeCall( cudaMemcpyToSymbol(c_lut, lut, 256 * sizeof(int), 0, cudaMemcpyDeviceToDevice) );
        else
            cudaSafeCall( cudaMemcpyToSymbolAsync(c_lut, lut, 256 * sizeof(int), 0, cudaMemcpyDeviceToDevice, stream) );

        const float scale = 255.0f / (src.cols * src.rows);

        transform(src, dst, EqualizeHist(scale), WithOutMask(), stream);
    }
}

#endif /* CUDA_DISABLER */
