for filter in 0..num_filters
    for channel in 0..input_channels
        for out_h in 0..output_height
            for out_w in 0..output_width
                for k_h in 0..kernel_height
                    for k_w in 0..kernel_width
                        output[filter, out_h, out_w] += 
                            kernel[filter, channel, k_h, k_w] * 
                            input[channel, out_h + k_h, out_w + k_w]