main.c

#include <stdio.h>
#include <string.h>
#include <CL/cl.h>

int main() {
	// Find the first GPU device
	cl_device_id device = 0;
	
	cl_uint platform_count = 0;
	clGetPlatformIDs(0, NULL, &platform_count);
	cl_platform_id platform_ids[platform_count];
	clGetPlatformIDs(platform_count, platform_ids, &platform_count);
	
	size_t i;
	for(i = 0; i < platform_count; i++) {
		cl_platform_id platform_id = platform_ids[i];
		
		cl_uint device_count = 0;
		clGetDeviceIDs(platform_id, CL_DEVICE_TYPE_GPU, 0, NULL, &device_count);
		cl_device_id device_ids[device_count];
		clGetDeviceIDs(platform_id, CL_DEVICE_TYPE_GPU, device_count, device_ids, &device_count);
		
		if (device_count > 0) {
			device = device_ids[0];
			break;
		}
	}
	
	if (!device) {
		fprintf(stderr, "Failed to find any OpenCL GPU device. Sorry.\n");
		return 1;
	}
	
	
	// Setup OpenCL
	cl_context context = clCreateContext(NULL, 1, &device, NULL, NULL, NULL);
	cl_command_queue command_queue = clCreateCommandQueue(context, device, 0, NULL);
	
	// Compile the kernel
	const char* program_code = ""
		"kernel void main(global uchar* in, global uchar* out)\n"
		"{\n"
		"	size_t i = get_global_id(0);\n"
		"	out[i] = in[i] - 3;\n"
		"}\n"
	;
	cl_program program = clCreateProgramWithSource(context, 1, (const char*[]){program_code}, NULL, NULL);
	cl_int error = clBuildProgram(program, 0, NULL, "", NULL, NULL);
	if (error) {
		char compiler_log[4096];
		clGetProgramBuildInfo(program, device, CL_PROGRAM_BUILD_LOG, sizeof(compiler_log), compiler_log, NULL);
		printf("OpenCL compiler failed:\n%s", compiler_log);
		return 2;
	}
	cl_kernel kernel = clCreateKernel(program, "main", NULL);
	
	// Setup GPU buffers
	char* transformed = "Khoor#Zruog$";
	size_t transformed_length = strlen(transformed);
	cl_mem buffer_in = clCreateBuffer(context, CL_MEM_READ_ONLY | CL_MEM_COPY_HOST_PTR, transformed_length, transformed, NULL);
	cl_mem buffer_out = clCreateBuffer(context, CL_MEM_WRITE_ONLY, transformed_length, NULL, NULL);
	
	// Execute kernel
	clSetKernelArg(kernel, 0, sizeof(buffer_in), &buffer_in);
	clSetKernelArg(kernel, 1, sizeof(buffer_out), &buffer_out);
	clEnqueueNDRangeKernel(command_queue, kernel, 1, NULL, (const size_t[]){ transformed_length }, NULL, 0, NULL, NULL);
	
	// Output result
	char* result = clEnqueueMapBuffer(command_queue, buffer_out, CL_TRUE, CL_MAP_READ, 0, transformed_length, 0, NULL, NULL, NULL);
		printf("in:  %.*s\n", (int)transformed_length, transformed);
		printf("out: %.*s\n", (int)transformed_length, result);
	clEnqueueUnmapMemObject(command_queue, buffer_out, result, 0, NULL, NULL);
	
	// Clean up
	clReleaseMemObject(buffer_in);
	clReleaseMemObject(buffer_out);
	clReleaseProgram(program);
	clReleaseCommandQueue(command_queue);
	clReleaseContext(context);
	
	return 0;
}