# dct

**Repository Path**: fsfzp888_admin/dct

## Basic Information

- **Project Name**: dct
- **Description**: 二维离散余弦正弦变换
支持2D DCT/DST/DSCT/DCST
openmp/cuda并行
- **Primary Language**: C++
- **License**: BSD-3-Clause
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2022-11-04
- **Last Updated**: 2024-05-31

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

# dct

#### 介绍
离散余弦正弦变换

#### 使用说明
参考main.cpp的用法，比如进行二维的DCT或者DST变换：
``` c++
        unsigned int dim = 4096;
	std::vector<float> data(dim * dim);
	for (unsigned int r = 0; r < dim; ++r)
	{
		for (unsigned int c = 0; c < dim; ++c)
		{
			data[r * dim + c] = (float)rand() / (RAND_MAX - 1);
		}
	}
	auto data2 = data;
	dct::transpose(data.data(), data2.data(), dim, dim);
	for (unsigned int r = 0; r < dim; ++r)
	{
		for (unsigned int c = 0; c < dim; ++c)
		{
			assert(data[r * dim + c] == data2[c * dim + r]);
		}
	}
	std::vector<float> cos_dct(dim), cos_idct(dim);
	dct::precompute_dct_cos(cos_dct.data(), dim);
	dct::precompute_idct_cos(cos_idct.data(), dim);
	std::vector<float> out1(dim * dim), out2(dim * dim), buf(dim * dim);
	clock_t start_time, end_time;
	start_time = clock();
	dct::dct2d(data.data(), out1.data(), buf.data(), cos_dct.data(), cos_dct.data(), dim, dim, 1);
	end_time = clock();
	std::cout << "dct2d time: " << (double)(end_time - start_time) / CLOCKS_PER_SEC << std::endl;
	start_time = clock();
	dct::idct2d(out1.data(), out2.data(), buf.data(), cos_idct.data(), cos_idct.data(), dim, dim, 1);
	end_time = clock();
	std::cout << "idct2d time: " << (double)(end_time - start_time) / CLOCKS_PER_SEC << std::endl;
	double sum1 = 0.0, sum2 = 0.0;
	for (unsigned int r = 0; r < dim; ++r)
	{
		for (unsigned int c = 0; c < dim; ++c)
		{
			double dr = (data[r * dim + c] - out2[r * dim + c]);
			sum1 += dr * dr;
			sum2 += data[r * dim + c] * out2[r * dim + c];
		}
	}
	std::cout << std::sqrt(sum1 / sum2) << std::endl;
	start_time = clock();
	dct::dst2d(data.data(), out1.data(), buf.data(), cos_dct.data(), cos_dct.data(), dim, dim, 1);
	end_time = clock();
	std::cout << "dst2d time: " << (double)(end_time - start_time) / CLOCKS_PER_SEC << std::endl;
	start_time = clock();
	dct::idst2d(out1.data(), out2.data(), buf.data(), cos_idct.data(), cos_idct.data(), dim, dim, 1);
	end_time = clock();
	std::cout << "idst2d time: " << (double)(end_time - start_time) / CLOCKS_PER_SEC << std::endl;
	sum1 = 0.0;
	sum2 = 0.0;
	for (unsigned int r = 0; r < dim; ++r)
	{
		for (unsigned int c = 0; c < dim; ++c)
		{
			double dr = (data[r * dim + c] - out2[r * dim + c]);
			sum1 += dr * dr;
			sum2 += data[r * dim + c] * out2[r * dim + c];
		}
	}
	std::cout << std::sqrt(sum1 / sum2) << std::endl;
```
也支持二维的DSCT和DCST变换

## 对比GPU运行速度
GPU: RTX 4090
结果

``` txt
dim is 4096x4096
CPU dct2d time: 0.946874
CPU idct2d time: 0.861657
DCT/IDCT error:0.000355373
CPU dst2d time: 1.01149
CPU idst2d time: 0.914253
DST/IDST error:0.000946313

GPU Device 0 with compute capability 8.9
transpose error: 0
GPU dct2d time: 0.028985
GPU idct2d time: 0.027435
DCT/IDCT error: 0.000251305
GPU dst2d time: 0.02841
GPU idst2d time: 0.027059
DST/IDST error: 0.000355395

dim is 2048x2048
CPU dct2d time: 0.225318
CPU idct2d time: 0.194414
DCT/IDCT error:0.000225355
CPU dst2d time: 0.247617
CPU idst2d time: 0.216328
DST/IDST error:0.000594362

GPU Device 0 with compute capability 8.9
transpose error: 0
GPU dct2d time: 0.006581
GPU idct2d time: 0.005803
DCT/IDCT error: 0.000159346
GPU dst2d time: 0.00663
GPU idst2d time: 0.00589
DST/IDST error: 0.000225348

dim is 1024x1024
CPU dct2d time: 0.05079
CPU idct2d time: 0.047894
DCT/IDCT error:0.000128235
CPU dst2d time: 0.057469
CPU idst2d time: 0.049495
DST/IDST error:0.000342496

GPU Device 0 with compute capability 8.9
transpose error: 0
GPU dct2d time: 0.001625
GPU idct2d time: 0.001378
DCT/IDCT error: 9.06671e-05
GPU dst2d time: 0.001654
GPU idst2d time: 0.001373
DST/IDST error: 0.000128222

dim is 512x512
CPU dct2d time: 0.011406
CPU idct2d time: 0.010484
DCT/IDCT error:6.01641e-05
CPU dst2d time: 0.012733
CPU idst2d time: 0.011252
DST/IDST error:0.00015519

GPU Device 0 with compute capability 8.9
transpose error: 0
GPU dct2d time: 0.000582
GPU idct2d time: 0.00047
DCT/IDCT error: 4.25335e-05
GPU dst2d time: 0.000615
GPU idst2d time: 0.00048
DST/IDST error: 6.01513e-05
```

GPU版本仍有优化空间，可通过如下命令获取一些nsight的建议继续优化

``` bash
sudo /usr/local/cuda/bin/ncu ./dct_operator  > ../gpu_kernel_ns_result.txt
```