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//                           License Agreement
//                For Open Source Computer Vision Library
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// Copyright (c) 2016-2017 Fabian David Tschopp, all rights reserved.
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__kernel void col2im(const int n, __global const T* data_col,
                     const int data_col_offset,
                     const int channels,
                     const int height, const int width,
                     const int height_col, const int width_col,
                     const int coeff_h, const int coeff_w,
                     __global const T* biasvec,
                     const int bias_offset,
                     __global T* data_im,
                     const int data_im_offset)
{
    data_col = data_col + data_col_offset;
    biasvec = biasvec + bias_offset;
    data_im = data_im + data_im_offset;
    int index = get_global_id(0);

    if(index < n)
    {
        T val = 0.f;
        int w = index % width + PAD_W;
        int h = (index / width) % height + PAD_H;
        int c = index / (width * height);
        int h_col_start = (h < KERNEL_H) ? 0 : (h - KERNEL_H) / STRIDE_H + 1;
        int h_col_end = min(h / STRIDE_H + 1, height_col);
        int plane_size_col = height_col * width_col;
        int offset = (c * KERNEL_H * KERNEL_W + h * KERNEL_W + w) * plane_size_col;

        int w_col_start = (w < KERNEL_W) ? 0 : (w - KERNEL_W) / STRIDE_W + 1;
        int w_col_end = min(w / STRIDE_W + 1, width_col);

        for (int h_col = h_col_start; h_col < h_col_end; ++h_col)
            for (int w_col = w_col_start; w_col < w_col_end; ++w_col)
                val += data_col[offset + h_col * coeff_h + w_col * coeff_w];

        data_im[index] = val + biasvec[c];
    }
}