OpenCL

Overview 

• OpenCL Presentation on SIGGRAPH 2008

Introduction

• Hello OpenCL

// Hello World for OpenCL
// Copyright 2009 David Black-Schaffer
//

#include "OpenCL/opencl.h"
#include 
#include 

#define LENGTH 10240


// Define our kernel. It just calculates the sin of the input data.
char *source = {
 "kernel calcSin(global float *data) {\n"
 "  int id = get_global_id(0);\n"
 "  data[id] = sin(data[id]);\n"
 "}\n"
};

// Note: there is no error handling here. This is bad practice in general.

int main (int argc, const char * argv[]) {
 
 // OpenCL Objects
 cl_device_id device;
 cl_context context;
 cl_command_queue queue;
 cl_program program;
 cl_kernel kernel;
 cl_mem buffer; 
 
 
 
 // Create and initialize the input data
 cl_float *data;
 data = (cl_float*)malloc(sizeof(cl_float)*LENGTH);

 for (int i=0; iLENGTH; i++) 
 {
  data[i] = i;
 }
 
 
 
 // Setup OpenCL
 clGetDeviceIDs(NULL, CL_DEVICE_TYPE_DEFAULT, 1, &device, NULL);
 context = clCreateContext(NULL, 1, &device, NULL, NULL, NULL);
 queue = clCreateCommandQueue(context, device, (cl_command_queue_properties)0, NULL);
 
 
 
 // Setup the input
 buffer = clCreateBuffer(context, CL_MEM_COPY_HOST_PTR, sizeof(cl_float)*10240, data, NULL);
 
 
 
 // Build the kernel
 program = clCreateProgramWithSource(context, 1, (const char**)&source, NULL, NULL);
 clBuildProgram(program, 0, NULL, NULL, NULL, NULL);
 kernel = clCreateKernel(program, "calcSin", NULL);
 
 
 
 // Execute the kernel
 clSetKernelArg(kernel, 0, sizeof(buffer), &buffer);
 size_t global_dimensions[] = {LENGTH,0,0};
 clEnqueueNDRangeKernel(queue, kernel, 1, NULL, global_dimensions, NULL, 0, NULL, NULL);
 
 
 
 // Read back the results
 clEnqueueReadBuffer(queue, buffer, CL_TRUE, 0, sizeof(cl_float)*LENGTH, data, 0, NULL, NULL);
 
 
 
 // Clean up
 clReleaseMemObject(buffer);
 clReleaseKernel(kernel);
 clReleaseProgram(program);
 clReleaseCommandQueue(queue);
 clReleaseContext(context);
 
 
 
 // Print out the results
 for (int i=0; i LENGTH; i++)
  printf("sin(%d) = %f\n", i, data[i]);
 
 
 
 free(data);
}