CUDA学习笔记三

HOG行人检测算法CUDA并行实现 这个版本的封装级别还不是特别高 所以很多还是可以看懂

这个示例可以看到写并行程序的不易 首先要对算法的实现有十分清晰的理解 也展现了很多CUDA优化的方法 包括shared memory的使用 循环展开

#include "internal_shared.hpp"

#ifndef CV_PI_F
  #ifndef CV_PI
    #define CV_PI_F 3.14159265f
  #else
    #define CV_PI_F ((float)CV_PI)
  #endif
#endif

// Other values are not supported
#define CELL_WIDTH 8
#define CELL_HEIGHT 8
#define CELLS_PER_BLOCK_X 2
#define CELLS_PER_BLOCK_Y 2

namespace cv { namespace gpu { namespace hog {

__constant__ int cnbins;
__constant__ int cblock_stride_x;
__constant__ int cblock_stride_y;
__constant__ int cnblocks_win_x;
__constant__ int cnblocks_win_y;
__constant__ int cblock_hist_size;
__constant__ int cblock_hist_size_2up;
__constant__ int cdescr_size;
__constant__ int cdescr_width;


/* Returns the nearest upper power of two, works only for 
the typical GPU thread count (pert block) values */
int power_2up(unsigned int n)
{
    if (n < 1) return 1;
    else if (n < 2) return 2;
    else if (n < 4) return 4;
    else if (n < 8) return 8;
    else if (n < 16) return 16;
    else if (n < 32) return 32;
    else if (n < 64) return 64;
    else if (n < 128) return 128;
    else if (n < 256) return 256;
    else if (n < 512) return 512;
    else if (n < 1024) return 1024;
    return -1; // Input is too big
}


void set_up_constants(int nbins, int block_stride_x, int block_stride_y, 
                      int nblocks_win_x, int nblocks_win_y)
{
    uploadConstant("cv::gpu::hog::cnbins", nbins);
    uploadConstant("cv::gpu::hog::cblock_stride_x", block_stride_x);
    uploadConstant("cv::gpu::hog::cblock_stride_y", block_stride_y);
    uploadConstant("cv::gpu::hog::cnblocks_win_x", nblocks_win_x);
    uploadConstant("cv::gpu::hog::cnblocks_win_y", nblocks_win_y);

    int block_hist_size = nbins * CELLS_PER_BLOCK_X * CELLS_PER_BLOCK_Y;
    uploadConstant("cv::gpu::hog::cblock_hist_size", block_hist_size);

    int block_hist_size_2up = power_2up(block_hist_size);    
    uploadConstant("cv::gpu::hog::cblock_hist_size_2up", block_hist_size_2up);

    int descr_width = nblocks_win_x * block_hist_size;
    uploadConstant("cv::gpu::hog::cdescr_width", descr_width);

    int descr_size = descr_width * nblocks_win_y;
    uploadConstant("cv::gpu::hog::cdescr_size", descr_size);
}


//----------------------------------------------------------------------------
// Histogram computation


template  // Number of histogram blocks processed by single GPU thread block
__global__ void compute_hists_kernel_many_blocks(const int img_block_width, const PtrElemStepf grad, 
                                                 const PtrElemStep qangle, float scale, float* block_hists)
{
    const int block_x = threadIdx.z;
    const int cell_x = threadIdx.x / 16;
    const int cell_y = threadIdx.y;
    const int cell_thread_x = threadIdx.x & 0xF;

    if (blockIdx.x * blockDim.z + block_x >= img_block_width)
        return;

    extern __shared__ float smem[];
    float* hists = smem;
    float* final_hist = smem + cnbins * 48 * nblocks;

    const int offset_x = (blockIdx.x * blockDim.z + block_x) * cblock_stride_x + 
                         4 * cell_x + cell_thread_x;
    const int offset_y = blockIdx.y * cblock_stride_y + 4 * cell_y;

    const float* grad_ptr = grad.ptr(offset_y) + offset_x * 2;
    const unsigned char* qangle_ptr = qangle.ptr(offset_y) + offset_x * 2;

    // 12 means that 12 pixels affect on block's cell (in one row)
    if (cell_thread_x < 12)
    {
        float* hist = hists + 12 * (cell_y * blockDim.z * CELLS_PER_BLOCK_Y + 
                                    cell_x + block_x * CELLS_PER_BLOCK_X) + 
                                   cell_thread_x;
        for (int bin_id = 0; bin_id < cnbins; ++bin_id)
            hist[bin_id * 48 * nblocks] = 0.f;

        const int dist_x = -4 + (int)cell_thread_x - 4 * cell_x;

        const int dist_y_begin = -4 - 4 * (int)threadIdx.y;
        for (int dist_y = dist_y_begin; dist_y < dist_y_begin + 12; ++dist_y)
        {
            float2 vote = *(const float2*)grad_ptr;
            uchar2 bin = *(const uchar2*)qangle_ptr;

            grad_ptr += grad.step;
            qangle_ptr += qangle.step;

            int dist_center_y = dist_y - 4 * (1 - 2 * cell_y);
            int dist_center_x = dist_x - 4 * (1 - 2 * cell_x);

            float gaussian = expf(-(dist_center_y * dist_center_y + 
                                    dist_center_x * dist_center_x) * scale);
            float interp_weight = (8.f - fabs(dist_y + 0.5f)) * 
                                  (8.f - fabs(dist_x + 0.5f)) / 64.f;

            hist[bin.x * 48 * nblocks] += gaussian * interp_weight * vote.x;
            hist[bin.y * 48 * nblocks] += gaussian * interp_weight * vote.y;
        }

        volatile float* hist_ = hist;
        for (int bin_id = 0; bin_id < cnbins; ++bin_id, hist_ += 48 * nblocks)
        {
            if (cell_thread_x < 6) hist_[0] += hist_[6];
            if (cell_thread_x < 3) hist_[0] += hist_[3];
            if (cell_thread_x == 0) 
                final_hist[((cell_x + block_x * 2) * 2 + cell_y) * cnbins + bin_id] 
                    = hist_[0] + hist_[1] + hist_[2];
        }
    }

    __syncthreads();

    float* block_hist = block_hists + (blockIdx.y * img_block_width + 
                                       blockIdx.x * blockDim.z + block_x) * 
                                      cblock_hist_size;        

    int tid = (cell_y * CELLS_PER_BLOCK_Y + cell_x) * 16 + cell_thread_x;
    if (tid < cblock_hist_size)
        block_hist[tid] = final_hist[block_x * cblock_hist_size + tid];     
}


void compute_hists(int nbins, int block_stride_x, int block_stride_y, 
                   int height, int width, const DevMem2Df& grad, 
                   const DevMem2D& qangle, float sigma, float* block_hists)                             
{
    const int nblocks = 1;

    int img_block_width = (width - CELLS_PER_BLOCK_X * CELL_WIDTH + block_stride_x) / 
                          block_stride_x;
    int img_block_height = (height - CELLS_PER_BLOCK_Y * CELL_HEIGHT + block_stride_y) / 
                           block_stride_y;

    dim3 grid(divUp(img_block_width, nblocks), img_block_height);
    dim3 threads(32, 2, nblocks);

    cudaSafeCall(cudaFuncSetCacheConfig(compute_hists_kernel_many_blocks, 
                                        cudaFuncCachePreferL1));
 
    // Precompute gaussian spatial window parameter
    float scale = 1.f / (2.f * sigma * sigma);

    int hists_size = (nbins * CELLS_PER_BLOCK_X * CELLS_PER_BLOCK_Y * 12 * nblocks) * sizeof(float);
    int final_hists_size = (nbins * CELLS_PER_BLOCK_X * CELLS_PER_BLOCK_Y * nblocks) * sizeof(float);
    int smem = hists_size + final_hists_size;
    compute_hists_kernel_many_blocks<<>>(
        img_block_width, grad, qangle, scale, block_hists);
    cudaSafeCall( cudaGetLastError() );

    cudaSafeCall( cudaDeviceSynchronize() );
}


//-------------------------------------------------------------
//  Normalization of histograms via L2Hys_norm
//


template 
__device__ float reduce_smem(volatile float* smem)
{        
    unsigned int tid = threadIdx.x;
    float sum = smem[tid];

    if (size >= 512) { if (tid < 256) smem[tid] = sum = sum + smem[tid + 256]; __syncthreads(); }
    if (size >= 256) { if (tid < 128) smem[tid] = sum = sum + smem[tid + 128]; __syncthreads(); }
    if (size >= 128) { if (tid < 64) smem[tid] = sum = sum + smem[tid + 64]; __syncthreads(); }
    
    if (tid < 32)
    {        
        if (size >= 64) smem[tid] = sum = sum + smem[tid + 32];
        if (size >= 32) smem[tid] = sum = sum + smem[tid + 16];
        if (size >= 16) smem[tid] = sum = sum + smem[tid + 8];
        if (size >= 8) smem[tid] = sum = sum + smem[tid + 4];
        if (size >= 4) smem[tid] = sum = sum + smem[tid + 2];
        if (size >= 2) smem[tid] = sum = sum + smem[tid + 1];
    }

    __syncthreads();
    sum = smem[0];
    
    return sum;
}


template  // Number of block hisograms processed by one GPU thread block
__global__ void normalize_hists_kernel_many_blocks(const int block_hist_size,
                                                   const int img_block_width, 
                                                   float* block_hists, float threshold)
{
    if (blockIdx.x * blockDim.z + threadIdx.z >= img_block_width)
        return;

    float* hist = block_hists + (blockIdx.y * img_block_width + 
                                 blockIdx.x * blockDim.z + threadIdx.z) * 
                                block_hist_size + threadIdx.x;
    
    __shared__ float sh_squares[nthreads * nblocks];
    float* squares = sh_squares + threadIdx.z * nthreads;
    
    float elem = 0.f;
    if (threadIdx.x < block_hist_size)
        elem = hist[0];
    
    squares[threadIdx.x] = elem * elem;        

    __syncthreads();
    float sum = reduce_smem(squares);
    
    float scale = 1.0f / (sqrtf(sum) + 0.1f * block_hist_size);        
    elem = min(elem * scale, threshold);
    
    __syncthreads();
    squares[threadIdx.x] = elem * elem;

    __syncthreads();
    sum = reduce_smem(squares);
    scale = 1.0f / (sqrtf(sum) + 1e-3f);
    
    if (threadIdx.x < block_hist_size)
        hist[0] = elem * scale;
}


void normalize_hists(int nbins, int block_stride_x, int block_stride_y, 
                     int height, int width, float* block_hists, float threshold)
{   
    const int nblocks = 1;

    int block_hist_size = nbins * CELLS_PER_BLOCK_X * CELLS_PER_BLOCK_Y;
    int nthreads = power_2up(block_hist_size);
    dim3 threads(nthreads, 1, nblocks);

    int img_block_width = (width - CELLS_PER_BLOCK_X * CELL_WIDTH + block_stride_x) / block_stride_x;
    int img_block_height = (height - CELLS_PER_BLOCK_Y * CELL_HEIGHT + block_stride_y) / block_stride_y;
    dim3 grid(divUp(img_block_width, nblocks), img_block_height);

    if (nthreads == 32)
        normalize_hists_kernel_many_blocks<32, nblocks><<>>(block_hist_size, img_block_width, block_hists, threshold);
    else if (nthreads == 64)
        normalize_hists_kernel_many_blocks<64, nblocks><<>>(block_hist_size, img_block_width, block_hists, threshold);
    else if (nthreads == 128)
        normalize_hists_kernel_many_blocks<64, nblocks><<>>(block_hist_size, img_block_width, block_hists, threshold);
    else if (nthreads == 256)
        normalize_hists_kernel_many_blocks<256, nblocks><<>>(block_hist_size, img_block_width, block_hists, threshold);
    else if (nthreads == 512)
        normalize_hists_kernel_many_blocks<512, nblocks><<>>(block_hist_size, img_block_width, block_hists, threshold);
    else
        cv::gpu::error("normalize_hists: histogram's size is too big, try to decrease number of bins", __FILE__, __LINE__);

    cudaSafeCall( cudaGetLastError() );

    cudaSafeCall( cudaDeviceSynchronize() );
}


//---------------------------------------------------------------------
//  Linear SVM based classification
//


template  // Number of histogram block processed by single GPU thread block
__global__ void classify_hists_kernel_many_blocks(const int img_win_width, const int img_block_width, 
                                                  const int win_block_stride_x, const int win_block_stride_y,
                                                  const float* block_hists, const float* coefs,
                                                  float free_coef, float threshold, unsigned char* labels)
{            
    const int win_x = threadIdx.z;
    if (blockIdx.x * blockDim.z + win_x >= img_win_width)
        return;

    const float* hist = block_hists + (blockIdx.y * win_block_stride_y * img_block_width + 
                                       blockIdx.x * win_block_stride_x * blockDim.z + win_x) * 
                                      cblock_hist_size;

    float product = 0.f;
    for (int i = threadIdx.x; i < cdescr_size; i += nthreads)
    {
        int offset_y = i / cdescr_width;
        int offset_x = i - offset_y * cdescr_width;
        product += coefs[i] * hist[offset_y * img_block_width * cblock_hist_size + offset_x];
    }

    __shared__ float products[nthreads * nblocks];

    const int tid = threadIdx.z * nthreads + threadIdx.x;
    products[tid] = product;

    __syncthreads();

    if (nthreads >= 512) 
    { 
        if (threadIdx.x < 256) products[tid] = product = product + products[tid + 256];
        __syncthreads(); 
    }
    if (nthreads >= 256) 
    { 
        if (threadIdx.x < 128) products[tid] = product = product + products[tid + 128]; 
        __syncthreads(); 
    }
    if (nthreads >= 128) 
    { 
        if (threadIdx.x < 64) products[tid] = product = product + products[tid + 64]; 
        __syncthreads(); 
    }
    
    if (threadIdx.x < 32)
    {        
        volatile float* smem = products;
        if (nthreads >= 64) smem[tid] = product = product + smem[tid + 32];
        if (nthreads >= 32) smem[tid] = product = product + smem[tid + 16];
        if (nthreads >= 16) smem[tid] = product = product + smem[tid + 8];
        if (nthreads >= 8) smem[tid] = product = product + smem[tid + 4];
        if (nthreads >= 4) smem[tid] = product = product + smem[tid + 2];
        if (nthreads >= 2) smem[tid] = product = product + smem[tid + 1];
    }

    if (threadIdx.x == 0)
        labels[blockIdx.y * img_win_width + blockIdx.x * blockDim.z + win_x] = (product + free_coef >= threshold);
}


void classify_hists(int win_height, int win_width, int block_stride_y, int block_stride_x, 
                    int win_stride_y, int win_stride_x, int height, int width, float* block_hists, 
                    float* coefs, float free_coef, float threshold, unsigned char* labels)
{   
    const int nthreads = 256;
    const int nblocks = 1;

    int win_block_stride_x = win_stride_x / block_stride_x;
    int win_block_stride_y = win_stride_y / block_stride_y;
    int img_win_width = (width - win_width + win_stride_x) / win_stride_x;
    int img_win_height = (height - win_height + win_stride_y) / win_stride_y;

    dim3 threads(nthreads, 1, nblocks);
    dim3 grid(divUp(img_win_width, nblocks), img_win_height);

    cudaSafeCall(cudaFuncSetCacheConfig(classify_hists_kernel_many_blocks, cudaFuncCachePreferL1));

    int img_block_width = (width - CELLS_PER_BLOCK_X * CELL_WIDTH + block_stride_x) / block_stride_x;
    classify_hists_kernel_many_blocks<<>>(
        img_win_width, img_block_width, win_block_stride_x, win_block_stride_y, 
        block_hists, coefs, free_coef, threshold, labels);
    cudaSafeCall( cudaGetLastError() );

    cudaSafeCall( cudaDeviceSynchronize() );
}

//----------------------------------------------------------------------------
// Extract descriptors


template 
__global__ void extract_descrs_by_rows_kernel(const int img_block_width, const int win_block_stride_x, const int win_block_stride_y, 
											  const float* block_hists, PtrElemStepf descriptors)
{
    // Get left top corner of the window in src
    const float* hist = block_hists + (blockIdx.y * win_block_stride_y * img_block_width + 
                                       blockIdx.x * win_block_stride_x) * cblock_hist_size;

    // Get left top corner of the window in dst
    float* descriptor = descriptors.ptr(blockIdx.y * gridDim.x + blockIdx.x);

    // Copy elements from src to dst
    for (int i = threadIdx.x; i < cdescr_size; i += nthreads)
    {
        int offset_y = i / cdescr_width;
        int offset_x = i - offset_y * cdescr_width;
        descriptor[i] = hist[offset_y * img_block_width * cblock_hist_size + offset_x];
    }
}


void extract_descrs_by_rows(int win_height, int win_width, int block_stride_y, int block_stride_x, int win_stride_y, int win_stride_x, 
							int height, int width, float* block_hists, DevMem2Df descriptors)
{
    const int nthreads = 256;

    int win_block_stride_x = win_stride_x / block_stride_x;
    int win_block_stride_y = win_stride_y / block_stride_y;
    int img_win_width = (width - win_width + win_stride_x) / win_stride_x;
    int img_win_height = (height - win_height + win_stride_y) / win_stride_y;
    dim3 threads(nthreads, 1);
    dim3 grid(img_win_width, img_win_height);

    int img_block_width = (width - CELLS_PER_BLOCK_X * CELL_WIDTH + block_stride_x) / block_stride_x;
    extract_descrs_by_rows_kernel<<>>(
        img_block_width, win_block_stride_x, win_block_stride_y, block_hists, descriptors);
    cudaSafeCall( cudaGetLastError() );

    cudaSafeCall( cudaDeviceSynchronize() );
}


template 
__global__ void extract_descrs_by_cols_kernel(const int img_block_width, const int win_block_stride_x, 
                                              const int win_block_stride_y, const float* block_hists, 
                                              PtrElemStepf descriptors)
{
    // Get left top corner of the window in src
    const float* hist = block_hists + (blockIdx.y * win_block_stride_y * img_block_width + 
                                       blockIdx.x * win_block_stride_x) * cblock_hist_size;

    // Get left top corner of the window in dst
    float* descriptor = descriptors.ptr(blockIdx.y * gridDim.x + blockIdx.x);

    // Copy elements from src to dst
    for (int i = threadIdx.x; i < cdescr_size; i += nthreads)
    {
        int block_idx = i / cblock_hist_size;
        int idx_in_block = i - block_idx * cblock_hist_size;

        int y = block_idx / cnblocks_win_x;
        int x = block_idx - y * cnblocks_win_x;

        descriptor[(x * cnblocks_win_y + y) * cblock_hist_size + idx_in_block] 
            = hist[(y * img_block_width  + x) * cblock_hist_size + idx_in_block];
    }
}


void extract_descrs_by_cols(int win_height, int win_width, int block_stride_y, int block_stride_x, 
                            int win_stride_y, int win_stride_x, int height, int width, float* block_hists, 
                            DevMem2Df descriptors)
{
    const int nthreads = 256;

    int win_block_stride_x = win_stride_x / block_stride_x;
    int win_block_stride_y = win_stride_y / block_stride_y;
    int img_win_width = (width - win_width + win_stride_x) / win_stride_x;
    int img_win_height = (height - win_height + win_stride_y) / win_stride_y;
    dim3 threads(nthreads, 1);
    dim3 grid(img_win_width, img_win_height);

    int img_block_width = (width - CELLS_PER_BLOCK_X * CELL_WIDTH + block_stride_x) / block_stride_x;
    extract_descrs_by_cols_kernel<<>>(
        img_block_width, win_block_stride_x, win_block_stride_y, block_hists, descriptors);
    cudaSafeCall( cudaGetLastError() );

    cudaSafeCall( cudaDeviceSynchronize() );
}

//----------------------------------------------------------------------------
// Gradients computation


template 
__global__ void compute_gradients_8UC4_kernel(int height, int width, const PtrElemStep img, 
                                              float angle_scale, PtrElemStepf grad, PtrElemStep qangle)
{
    const int x = blockIdx.x * blockDim.x + threadIdx.x;

    const uchar4* row = (const uchar4*)img.ptr(blockIdx.y);

    __shared__ float sh_row[(nthreads + 2) * 3];

    uchar4 val;
    if (x < width) 
        val = row[x]; 
    else 
        val = row[width - 2];

    sh_row[threadIdx.x + 1] = val.x;
    sh_row[threadIdx.x + 1 + (nthreads + 2)] = val.y;
    sh_row[threadIdx.x + 1 + 2 * (nthreads + 2)] = val.z;

    if (threadIdx.x == 0)
    {
        val = row[max(x - 1, 1)];
        sh_row[0] = val.x;
        sh_row[(nthreads + 2)] = val.y;
        sh_row[2 * (nthreads + 2)] = val.z;
    }

    if (threadIdx.x == blockDim.x - 1)
    {
        val = row[min(x + 1, width - 2)];
        sh_row[blockDim.x + 1] = val.x;
        sh_row[blockDim.x + 1 + (nthreads + 2)] = val.y;
        sh_row[blockDim.x + 1 + 2 * (nthreads + 2)] = val.z;
    }

    __syncthreads();
    if (x < width)
    {
        float3 a, b;

        b.x = sh_row[threadIdx.x + 2];
        b.y = sh_row[threadIdx.x + 2 + (nthreads + 2)];
        b.z = sh_row[threadIdx.x + 2 + 2 * (nthreads + 2)];
        a.x = sh_row[threadIdx.x];
        a.y = sh_row[threadIdx.x + (nthreads + 2)];
        a.z = sh_row[threadIdx.x + 2 * (nthreads + 2)];

        float3 dx;
        if (correct_gamma)
            dx = make_float3(sqrtf(b.x) - sqrtf(a.x), sqrtf(b.y) - sqrtf(a.y), sqrtf(b.z) - sqrtf(a.z));    
        else
            dx = make_float3(b.x - a.x, b.y - a.y, b.z - a.z);    

        float3 dy = make_float3(0.f, 0.f, 0.f);

        if (blockIdx.y > 0 && blockIdx.y < height - 1)
        {
            val = ((const uchar4*)img.ptr(blockIdx.y - 1))[x];
            a = make_float3(val.x, val.y, val.z);

            val = ((const uchar4*)img.ptr(blockIdx.y + 1))[x];
            b = make_float3(val.x, val.y, val.z);

            if (correct_gamma)
                dy = make_float3(sqrtf(b.x) - sqrtf(a.x), sqrtf(b.y) - sqrtf(a.y), sqrtf(b.z) - sqrtf(a.z));
            else
                dy = make_float3(b.x - a.x, b.y - a.y, b.z - a.z);
        }

        float best_dx = dx.x;
        float best_dy = dy.x;

        float mag0 = dx.x * dx.x + dy.x * dy.x;
        float mag1 = dx.y * dx.y + dy.y * dy.y;
        if (mag0 < mag1) 
        {
            best_dx = dx.y;
            best_dy = dy.y;
            mag0 = mag1;
        }

        mag1 = dx.z * dx.z + dy.z * dy.z;
        if (mag0 < mag1)
        {
            best_dx = dx.z;
            best_dy = dy.z;
            mag0 = mag1;
        }

        mag0 = sqrtf(mag0);

        float ang = (atan2f(best_dy, best_dx) + CV_PI_F) * angle_scale - 0.5f;
        int hidx = (int)floorf(ang);
        ang -= hidx;
        hidx = (hidx + cnbins) % cnbins;

        ((uchar2*)qangle.ptr(blockIdx.y))[x] = make_uchar2(hidx, (hidx + 1) % cnbins);
        ((float2*)grad.ptr(blockIdx.y))[x] = make_float2(mag0 * (1.f - ang), mag0 * ang);
    }
}


void compute_gradients_8UC4(int nbins, int height, int width, const DevMem2D& img, 
                            float angle_scale, DevMem2Df grad, DevMem2D qangle, bool correct_gamma)
{
    const int nthreads = 256;

    dim3 bdim(nthreads, 1);
    dim3 gdim(divUp(width, bdim.x), divUp(height, bdim.y));

    if (correct_gamma)
        compute_gradients_8UC4_kernel<<>>(height, width, img, angle_scale, grad, qangle);
    else
        compute_gradients_8UC4_kernel<<>>(height, width, img, angle_scale, grad, qangle);

    cudaSafeCall( cudaGetLastError() );

    cudaSafeCall( cudaDeviceSynchronize() );
}

template 
__global__ void compute_gradients_8UC1_kernel(int height, int width, const PtrElemStep img, 
                                              float angle_scale, PtrElemStepf grad, PtrElemStep qangle)
{
    const int x = blockIdx.x * blockDim.x + threadIdx.x;

    const unsigned char* row = (const unsigned char*)img.ptr(blockIdx.y);

    __shared__ float sh_row[nthreads + 2];

    if (x < width) 
        sh_row[threadIdx.x + 1] = row[x]; 
    else 
        sh_row[threadIdx.x + 1] = row[width - 2];

    if (threadIdx.x == 0)
        sh_row[0] = row[max(x - 1, 1)];

    if (threadIdx.x == blockDim.x - 1)
        sh_row[blockDim.x + 1] = row[min(x + 1, width - 2)];

    __syncthreads();
    if (x < width)
    {
        float dx;

        if (correct_gamma)
            dx = sqrtf(sh_row[threadIdx.x + 2]) - sqrtf(sh_row[threadIdx.x]);
        else
            dx = sh_row[threadIdx.x + 2] - sh_row[threadIdx.x];

        float dy = 0.f;
        if (blockIdx.y > 0 && blockIdx.y < height - 1)
        {
            float a = ((const unsigned char*)img.ptr(blockIdx.y + 1))[x];
            float b = ((const unsigned char*)img.ptr(blockIdx.y - 1))[x];
            if (correct_gamma)
                dy = sqrtf(a) - sqrtf(b);
            else
                dy = a - b;
        }
        float mag = sqrtf(dx * dx + dy * dy);

        float ang = (atan2f(dy, dx) + CV_PI_F) * angle_scale - 0.5f;
        int hidx = (int)floorf(ang);
        ang -= hidx;
        hidx = (hidx + cnbins) % cnbins;

        ((uchar2*)qangle.ptr(blockIdx.y))[x] = make_uchar2(hidx, (hidx + 1) % cnbins);
        ((float2*)  grad.ptr(blockIdx.y))[x] = make_float2(mag * (1.f - ang), mag * ang);
    }
}


void compute_gradients_8UC1(int nbins, int height, int width, const DevMem2D& img, 
                            float angle_scale, DevMem2Df grad, DevMem2D qangle, bool correct_gamma)
{
    const int nthreads = 256;

    dim3 bdim(nthreads, 1);
    dim3 gdim(divUp(width, bdim.x), divUp(height, bdim.y));

    if (correct_gamma)
        compute_gradients_8UC1_kernel<<>>(height, width, img, angle_scale, grad, qangle);
    else
        compute_gradients_8UC1_kernel<<>>(height, width, img, angle_scale, grad, qangle);

    cudaSafeCall( cudaGetLastError() );

    cudaSafeCall( cudaDeviceSynchronize() );
}



//-------------------------------------------------------------------
// Resize

texture resize8UC4_tex;
texture resize8UC1_tex;

__global__ void resize_for_hog_kernel(float sx, float sy, DevMem2D_ dst, int colOfs)
{
    unsigned int x = blockIdx.x * blockDim.x + threadIdx.x;
    unsigned int y = blockIdx.y * blockDim.y + threadIdx.y;

    if (x < dst.cols && y < dst.rows)
        dst.ptr(y)[x] = tex2D(resize8UC1_tex, x * sx + colOfs, y * sy) * 255;
}

__global__ void resize_for_hog_kernel(float sx, float sy, DevMem2D_ dst, int colOfs)
{
    unsigned int x = blockIdx.x * blockDim.x + threadIdx.x;
    unsigned int y = blockIdx.y * blockDim.y + threadIdx.y;

    if (x < dst.cols && y < dst.rows)
	{        
		float4 val = tex2D(resize8UC4_tex, x * sx + colOfs, y * sy);
        dst.ptr(y)[x] = make_uchar4(val.x * 255, val.y * 255, val.z * 255, val.w * 255);
	}
}

template 
static void resize_for_hog(const DevMem2D& src, DevMem2D dst, TEX& tex)
{
    tex.filterMode = cudaFilterModeLinear;

    size_t texOfs = 0;
    int colOfs = 0;

    cudaChannelFormatDesc desc = cudaCreateChannelDesc();    
    cudaSafeCall( cudaBindTexture2D(&texOfs, tex, src.data, desc, src.cols, src.rows, src.step) );

    if (texOfs != 0) 
    {
        colOfs = static_cast( texOfs/sizeof(T) );
        cudaSafeCall( cudaUnbindTexture(tex) );
        cudaSafeCall( cudaBindTexture2D(&texOfs, tex, src.data, desc, src.cols, src.rows, src.step) );
    }    

    dim3 threads(32, 8);
    dim3 grid(divUp(dst.cols, threads.x), divUp(dst.rows, threads.y));
    
	float sx = static_cast(src.cols) / dst.cols;
    float sy = static_cast(src.rows) / dst.rows;

    resize_for_hog_kernel<<>>(sx, sy, (DevMem2D_)dst, colOfs);
    cudaSafeCall( cudaGetLastError() );

    cudaSafeCall( cudaDeviceSynchronize() );

    cudaSafeCall( cudaUnbindTexture(tex) );
}

void resize_8UC1(const DevMem2D& src, DevMem2D dst) { resize_for_hog (src, dst, resize8UC1_tex); }
void resize_8UC4(const DevMem2D& src, DevMem2D dst) { resize_for_hog(src, dst, resize8UC4_tex); }

}}}