下面通过一个向量相加的程序来了解OpenCL . 有A，B两个四维向量，相加后值存在C向量里，openCL根据用户提供的维数，将向量分解成多个任务分发给DSP进行并行计算

openCL程序分为两个部份，一部份是内核代码，负责具体算法。另一部份是主程序负责初始化OpenCL和准备数据。主程序加载内核代码，并按照既定方法进行运算

kernel代码如下

__kernel voidvectoradd(__global int *a, __global int *b, __global int *c)

{

int id = get_global_id(0);

c[id] = a[id] + b[id];

}

__kernel 指明这是一个openCL内核，__global 说明指针指向的是全局的设备内存空间

HOST端代码如下

int get_ocl_string(const char *file_name, char *ocl_string)

{

FILE *fp;

int file_length;

int status = 0;

fp = fopen(file_name, "r");

if (fp == NULL)

return -1;

fseek(fp, 0, SEEK_END);

file_length = ftell(fp);

fseek(fp, 0, SEEK_SET);

status = fread(ocl_string, 1, file_length,fp);

if (status == -1)

return -1;

return file_length;

}

int main(void)

{

int array_a[10] = {0, 1, 2, 3, 4, 5, 6, 7,8, 9};

int array_b[10] = {9, 8, 7, 6, 5, 4, 3, 2,1, 0};

int array_c[10] = {0, 0, 0, 0, 0, 0, 0, 0,0, 0};

size_t datasize = 10 * sizeof(int);

size_t ocl_string_size;

char *ocl_string;

ocl_string = (char *)malloc(1024*1024);

cl_platform_id platform_id;

cl_device_id device_id;

cl_context context;

cl_command_queue command_queue;

cl_mem buffer_a, buffer_b, buffer_c;

cl_program program;

cl_kernel kernel;

clGetPlatformIDs(1, &platform_id,NULL);

clGetDeviceIDs(platform_id,CL_DEVICE_TYPE_ACCELERATOR, 1, &device_id, NULL);

//创建上下文

context = clCreateContext(NULL, 1,&device_id, NULL, NULL, NULL);

command_queue = clCreateCommandQueue(context,device_id, 0, NULL);

//分配内存

buffer_a = clCreateBuffer(context,CL_MEM_READ_ONLY, datasize, NULL, NULL);

buffer_b = clCreateBuffer(context,CL_MEM_READ_ONLY, datasize, NULL, NULL);

buffer_c = clCreateBuffer(context,CL_MEM_READ_ONLY, datasize, NULL, NULL);

//读取核函数，并且上传到DSP端

ocl_string_size =get_ocl_string("vectoradd.cl", ocl_string);

clEnqueueWriteBuffer(command_queue,buffer_a, CL_FALSE, 0, datasize, array_a, 0, NULL, NULL);

clEnqueueWriteBuffer(command_queue,buffer_b, CL_FALSE, 0, datasize, array_b, 0, NULL, NULL);

program =clCreateProgramWithSource(context, 1, (const char **)&ocl_string,&ocl_string_size, NULL);

clBuildProgram(program, 1, &device_id,NULL, NULL, NULL);

kernel = clCreateKernel(program,"vectoradd", NULL);

//传递参数

clSetKernelArg(kernel, 0,sizeof(cl_mem),&buffer_a);

clSetKernelArg(kernel, 1,sizeof(cl_mem),&buffer_b);

clSetKernelArg(kernel, 2,sizeof(cl_mem),&buffer_c);

size_t global_work_size[1] = {10};

//执行核函数

clEnqueueNDRangeKernel(command_queue,kernel, 1, NULL, global_work_size, NULL, 0, NULL, NULL);

//从核函数取回计算结果

clEnqueueReadBuffer(command_queue,buffer_c, CL_TRUE, 0, datasize, array_c, 0, NULL, NULL);

for (int i = 0 ; i < 10; i ++) {

printf("%d ", array_a);

}

printf("\n");

for (int i = 0 ; i < 10; i ++) {

printf("%d ", array_b);

}

printf("\n");

for (int i = 0 ; i < 10; i ++) {

printf("%d ", array_c);

}

printf("\n");

clReleaseKernel(kernel);

clReleaseProgram(program);

clReleaseCommandQueue(command_queue);

clReleaseMemObject(buffer_a);

clReleaseMemObject(buffer_b);

clReleaseMemObject(buffer_c);

clReleaseContext(context);

return 0;

}

将上述程序编译，结果如下

0 1 2 3 4 5 6 7 89

9 8 7 6 5 4 3 2 10

9 9 9 9 9 9 9 9 99