OpenCL-4-小试牛刀

前四章已经讲了那么多的概念，下面该真刀真枪地试一试了。

下面是宿主机端程序:

#include <stdio.h>
#include <stdlib.h>
#ifdef __APPLE__
#include <OpenCL/opencl.h>
#else
#include <CL/cl.h>
#endif

#define MAX_SOURCE_SIZE (0x100000)
int main(void) {
    //创建2个输入向量
    int i;
    const int LIST_SIZE=1024;
    int *A=(int*)malloc(sizeof(int)*LIST_SIZE);
    int *B=(int*)malloc(sizeof(int)*LIST_SIZE);
    for (i=0; i<LIST_SIZE; i++) {
        A[i]=i;
        B[i]=LIST_SIZE-i;
    }
    //载入内核源码到source_str
    FILE *fp;
    char *source_str;
    size_t source_size;
    fp=fopen("vector_add_kernel.cl","r");
    if (!fp) {
        fprintf(stderr, "Failed to load kernel\n");
        exit(1);
    }
    source_str=(char*)malloc(MAX_SOURCE_SIZE);
    source_size=fread(source_str,1,MAX_SOURCE_SIZE,fp);
    fclose(fp);
    //获得平台和设备信息
    cl_platform_id platform_id=NULL;
    cl_device_id device_id=NULL;
    cl_uint ret_num_devices;
    cl_uint ret_num_platforms;
    cl_int ret=clGetPlatformIDs(1, &platform_id, &ret_num_platforms);
    ret=clGetDeviceIDs(platform_id, CL_DEVICE_TYPE_DEFAULT, 1, &device_id, &ret_num_devices);
    //创建OpenCL上下文
    cl_context context=clCreateContext(NULL,1,&device_id,NULL,NULL,&ret);
    //创建命令队列
    cl_command_queue command_queue=clCreateCommandQueue(context,device_id,0,&ret);

    //创建内存缓冲对象，在设备上为每个向量
    cl_mem a_mem_obj=clCreateBuffer(context,CL_MEM_READ_ONLY,
            LIST_SIZE*sizeof(int),NULL,&ret);
    cl_mem b_mem_obj=clCreateBuffer(context,CL_MEM_READ_ONLY,
            LIST_SIZE*sizeof(int),NULL,&ret);
    cl_mem c_mem_obj=clCreateBuffer(context,CL_MEM_WRITE_ONLY,
    LIST_SIZE*sizeof(int),NULL,&ret);
    //拷贝数据A和B到对应的内存缓冲
    ret=clEnqueueWriteBuffer(command_queue,a_mem_obj,CL_TRUE,0,
    LIST_SIZE*sizeof(int),A,0,NULL,NULL);
    ret=clEnqueueWriteBuffer(command_queue,a_mem_obj,CL_TRUE,0,
    LIST_SIZE*sizeof(int),B,0,NULL,NULL);

    //创建程序
    cl_program program=clCreateProgramWithSource(context,1,
    (const char**)&source_str,(const size_t*)&source_size, &ret);
    //构建程序
    ret=clBuildProgram(program,1,&device_id,NULL,NULL,NULL);
    //创建OpenCL内核
    cl_kernel kernel=clCreateKernel(program,"vector_add",&ret);
    //设置内核参数
    ret=clSetKernelArg(kernel,0,sizeof(cl_mem),(void*)&a_mem_obj);
    ret=clSetKernelArg(kernel,1,sizeof(cl_mem),(void*)&b_mem_obj);
    ret=clSetKernelArg(kernel,2,sizeof(cl_mem),(void*)&c_mem_obj);
    //执行内核
    size_t global_item_size=LIST_SIZE;  //处理整个列表
    size_t local_item_size=64;          //分割为64个组
    ret=clEnqueueNDRangeKernel(command_queue,kernel,1,NULL,
    &global_item_size,&local_item_size,0,NULL,NULL);
    //读取内存缓冲C到本地变量C
    int *C=(int*)malloc(sizeof(int)*LIST_SIZE);
    ret=clEnqueueReadBuffer(command_queue,c_mem_obj,CL_TRUE,0,
    LIST_SIZE*sizeof(int),C,0,NULL,NULL);
    //显示结果
    for (i=0; i<LIST_SIZE; i++) {
        printf("%d + %d = %d\n", A[i], B[i], C[i]);
    }
    //清理资源
    ret=clFlush(command_queue);
    ret=clFinish(command_queue);
    ret=clReleaseKernel(kernel);
    ret=clReleaseProgram(program);
    ret=clReleaseMemObject(a_mem_obj);
    ret=clReleaseMemObject(b_mem_obj);
    ret=clReleaseMemObject(c_mem_obj);
    ret=clReleaseCommandQueue(command_queue);
    ret=clReleaseContext(context);
    free(A);
    free(B);
    free(C);
    return 0;
}

下面是内核程序（vector_add_kernel.cl）:

__kernel void vector_add(__global const int *A, __global const int *B, __global int *C) {
    //获得当前要处理元素的索
    int i=get_global_id(0);
    //做计算
    C[i]=A[i]+B[i];
}

之后使用命令：

gcc -o Test Test.c -I<Header_to_OpenCL_Path>

进行编译。

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原文地址：https://coderdock.com