cuda-samples/Samples/2_Concepts_and_Techniques/dct8x8/dct8x8_kernel_quantization.cuh

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/**
**************************************************************************
* \file dct8x8_kernel_quantization.cu
* \brief Contains unoptimized quantization routines. Device code.
*
* This code implements CUDA versions of quantization of Discrete Cosine
* Transform coefficients with 8x8 blocks for float and short arrays.
*/

#pragma once
#include <cooperative_groups.h>

namespace cg = cooperative_groups;
#include "Common.h"

/**
*  JPEG quality=0_of_12 quantization matrix
*/
__constant__ short Q[] = {
  32,  33,  51,  81,  66,  39,  34,  17,
  33,  36,  48,  47,  28,  23,  12,  12,
  51,  48,  47,  28,  23,  12,  12,  12,
  81,  47,  28,  23,  12,  12,  12,  12,
  66,  28,  23,  12,  12,  12,  12,  12,
  39,  23,  12,  12,  12,  12,  12,  12,
  34,  12,  12,  12,  12,  12,  12,  12,
  17,  12,  12,  12,  12,  12,  12,  12
};

/**
**************************************************************************
*  Performs in-place quantization of given DCT coefficients plane using
*  predefined quantization matrices (for floats plane). Unoptimized.
*
* \param SrcDst         [IN/OUT] - DCT coefficients plane
* \param Stride         [IN] - Stride of SrcDst
*
* \return None
*/
__global__ void CUDAkernelQuantizationFloat(float *SrcDst, int Stride) {
  // Block index
  int bx = blockIdx.x;
  int by = blockIdx.y;

  // Thread index (current coefficient)
  int tx = threadIdx.x;
  int ty = threadIdx.y;

  // copy current coefficient to the local variable
  float curCoef =
      SrcDst[(by * BLOCK_SIZE + ty) * Stride + (bx * BLOCK_SIZE + tx)];
  float curQuant = (float)Q[ty * BLOCK_SIZE + tx];

  // quantize the current coefficient
  float quantized = roundf(curCoef / curQuant);
  curCoef = quantized * curQuant;

  // copy quantized coefficient back to the DCT-plane
  SrcDst[(by * BLOCK_SIZE + ty) * Stride + (bx * BLOCK_SIZE + tx)] = curCoef;
}

/**
**************************************************************************
*  Performs in-place quantization of given DCT coefficients plane using
*  predefined quantization matrices (for shorts plane). Unoptimized.
*
* \param SrcDst         [IN/OUT] - DCT coefficients plane
* \param Stride         [IN] - Stride of SrcDst
*
* \return None
*/
__global__ void CUDAkernelQuantizationShort(short *SrcDst, int Stride) {
  // Handle to thread block group
  cg::thread_block cta = cg::this_thread_block();
  // Block index
  int bx = blockIdx.x;
  int by = blockIdx.y;

  // Thread index (current coefficient)
  int tx = threadIdx.x;
  int ty = threadIdx.y;

  // copy current coefficient to the local variable
  short curCoef =
      SrcDst[(by * BLOCK_SIZE + ty) * Stride + (bx * BLOCK_SIZE + tx)];
  short curQuant = Q[ty * BLOCK_SIZE + tx];

  // quantize the current coefficient
  if (curCoef < 0) {
    curCoef = -curCoef;
    curCoef += curQuant >> 1;
    curCoef /= curQuant;
    curCoef = -curCoef;
  } else {
    curCoef += curQuant >> 1;
    curCoef /= curQuant;
  }

  cg::sync(cta);

  curCoef = curCoef * curQuant;

  // copy quantized coefficient back to the DCT-plane
  SrcDst[(by * BLOCK_SIZE + ty) * Stride + (bx * BLOCK_SIZE + tx)] = curCoef;
}