Open CL program to convert from upper to lower case

tolower.c

#include <stdio.h>
#include "string.h"

#include <fcntl.h>
#include "CL/cl.h"

// #define DATA_SIZE 10
#define BUF_SIZE 128
#define ERROR -1

#define END 0

char *KernelSource = "";

char* read_file(char* filename, int* len) {
    int ip_file, rd_cnt, tot_cnt = 0;
    int buf_size = BUF_SIZE;
    char * tmp_buf = malloc(buf_size * sizeof(char));
    char * offset = tmp_buf;
    ip_file = open(filename, O_RDONLY);
    if ( ip_file == ERROR ) {
        perror("Error accessing file.");
        return (char*)-1;
    }
    do {
        rd_cnt = read(ip_file,offset,BUF_SIZE);
        offset += rd_cnt;
        tot_cnt += rd_cnt;
    }while(rd_cnt != END);
    (*len) = tot_cnt;
    return tmp_buf;
}

const char *getErrorString(cl_int error)
{
switch(error){
    // run-time and JIT compiler errors
    case 0: return "CL_SUCCESS";
    case -1: return "CL_DEVICE_NOT_FOUND";
    case -2: return "CL_DEVICE_NOT_AVAILABLE";
    case -3: return "CL_COMPILER_NOT_AVAILABLE";
    case -4: return "CL_MEM_OBJECT_ALLOCATION_FAILURE";
    case -5: return "CL_OUT_OF_RESOURCES";
    case -6: return "CL_OUT_OF_HOST_MEMORY";
    case -7: return "CL_PROFILING_INFO_NOT_AVAILABLE";
    case -8: return "CL_MEM_COPY_OVERLAP";
    case -9: return "CL_IMAGE_FORMAT_MISMATCH";
    case -10: return "CL_IMAGE_FORMAT_NOT_SUPPORTED";
    case -11: return "CL_BUILD_PROGRAM_FAILURE";
    case -12: return "CL_MAP_FAILURE";
    case -13: return "CL_MISALIGNED_SUB_BUFFER_OFFSET";
    case -14: return "CL_EXEC_STATUS_ERROR_FOR_EVENTS_IN_WAIT_LIST";
    case -15: return "CL_COMPILE_PROGRAM_FAILURE";
    case -16: return "CL_LINKER_NOT_AVAILABLE";
    case -17: return "CL_LINK_PROGRAM_FAILURE";
    case -18: return "CL_DEVICE_PARTITION_FAILED";
    case -19: return "CL_KERNEL_ARG_INFO_NOT_AVAILABLE";

    // compile-time errors
    case -30: return "CL_INVALID_VALUE";
    case -31: return "CL_INVALID_DEVICE_TYPE";
    case -32: return "CL_INVALID_PLATFORM";
    case -33: return "CL_INVALID_DEVICE";
    case -34: return "CL_INVALID_CONTEXT";
    case -35: return "CL_INVALID_QUEUE_PROPERTIES";
    case -36: return "CL_INVALID_COMMAND_QUEUE";
    case -37: return "CL_INVALID_HOST_PTR";
    case -38: return "CL_INVALID_MEM_OBJECT";
    case -39: return "CL_INVALID_IMAGE_FORMAT_DESCRIPTOR";
    case -40: return "CL_INVALID_IMAGE_SIZE";
    case -41: return "CL_INVALID_SAMPLER";
    case -42: return "CL_INVALID_BINARY";
    case -43: return "CL_INVALID_BUILD_OPTIONS";
    case -44: return "CL_INVALID_PROGRAM";
    case -45: return "CL_INVALID_PROGRAM_EXECUTABLE";
    case -46: return "CL_INVALID_KERNEL_NAME";
    case -47: return "CL_INVALID_KERNEL_DEFINITION";
    case -48: return "CL_INVALID_KERNEL";
    case -49: return "CL_INVALID_ARG_INDEX";
    case -50: return "CL_INVALID_ARG_VALUE";
    case -51: return "CL_INVALID_ARG_SIZE";
    case -52: return "CL_INVALID_KERNEL_ARGS";
    case -53: return "CL_INVALID_WORK_DIMENSION";
    case -54: return "CL_INVALID_WORK_GROUP_SIZE";
    case -55: return "CL_INVALID_WORK_ITEM_SIZE";
    case -56: return "CL_INVALID_GLOBAL_OFFSET";
    case -57: return "CL_INVALID_EVENT_WAIT_LIST";
    case -58: return "CL_INVALID_EVENT";
    case -59: return "CL_INVALID_OPERATION";
    case -60: return "CL_INVALID_GL_OBJECT";
    case -61: return "CL_INVALID_BUFFER_SIZE";
    case -62: return "CL_INVALID_MIP_LEVEL";
    case -63: return "CL_INVALID_GLOBAL_WORK_SIZE";
    case -64: return "CL_INVALID_PROPERTY";
    case -65: return "CL_INVALID_IMAGE_DESCRIPTOR";
    case -66: return "CL_INVALID_COMPILER_OPTIONS";
    case -67: return "CL_INVALID_LINKER_OPTIONS";
    case -68: return "CL_INVALID_DEVICE_PARTITION_COUNT";

    // extension errors
    case -1000: return "CL_INVALID_GL_SHAREGROUP_REFERENCE_KHR";
    case -1001: return "CL_PLATFORM_NOT_FOUND_KHR";
    case -1002: return "CL_INVALID_D3D10_DEVICE_KHR";
    case -1003: return "CL_INVALID_D3D10_RESOURCE_KHR";
    case -1004: return "CL_D3D10_RESOURCE_ALREADY_ACQUIRED_KHR";
    case -1005: return "CL_D3D10_RESOURCE_NOT_ACQUIRED_KHR";
    default: return "Unknown OpenCL error";
    }
}

int main(void)
{
    cl_context context;
    cl_context_properties properties[3];
    cl_kernel kernel;
    cl_command_queue command_queue;
    cl_program program;
    cl_int err;
    cl_uint num_of_platforms=0;
    cl_platform_id platform_id;
    cl_device_id device_id;
    cl_uint num_of_devices=0;
    cl_mem input, output;
    size_t global;
    int result;
    int len = 0;

    KernelSource = read_file("tolower.cl",&len);

    char inputData[]="SKGBKSLNVSKBVSJRV";
    int DATA_SIZE = strlen(inputData);
    char *results = (char*)malloc(sizeof(char)*DATA_SIZE);

    printf("%s\n",inputData);

    int i;

    // retreives a list of platforms available
    if (clGetPlatformIDs(1, &platform_id, &num_of_platforms)!= CL_SUCCESS)
    {
        printf("Unable to get platform_id\n");
        return 1;
    }

    // try to get a supported GPU device
    if (clGetDeviceIDs(platform_id, CL_DEVICE_TYPE_ALL, 1, &device_id, &num_of_devices) != CL_SUCCESS)
    {
        printf("Unable to get device_id\n");
        return 1;
    }

    // context properties list - must be terminated with 0
    properties[0]= CL_CONTEXT_PLATFORM;
    properties[1]= (cl_context_properties) platform_id;
    properties[2]= 0;

    // create a context with the GPU device
    context = clCreateContext(properties,1,&device_id,NULL,NULL,&err);

    // create command queue using the context and device
    command_queue = clCreateCommandQueue(context, device_id, 0, &err);

    // create a program from the kernel source code
    program = clCreateProgramWithSource(context,1,(const char **) &KernelSource, NULL, &err);

    // compile the program
    if (result = clBuildProgram(program, 0, NULL, NULL, NULL, NULL) != CL_SUCCESS)
    {
        printf("Error building program\n");
        printf("%s\n", getErrorString(result));
        return 1;
    }

    // specify which kernel from the program to execute
    kernel = clCreateKernel(program, "vector_add", &err);

    // create buffers for the input and ouput
    input = clCreateBuffer(context, CL_MEM_READ_ONLY, sizeof(char) * DATA_SIZE, NULL, NULL);
    output = clCreateBuffer(context, CL_MEM_WRITE_ONLY, sizeof(char) * DATA_SIZE, NULL, NULL);

    // load data into the input buffer
    clEnqueueWriteBuffer(command_queue, input, CL_TRUE, 0, sizeof(char) * DATA_SIZE, inputData, 0, NULL, NULL);

    // set the argument list for the kernel command
    clSetKernelArg(kernel, 0, sizeof(cl_mem), &input);
    clSetKernelArg(kernel, 1, sizeof(cl_mem), &output);
    global=DATA_SIZE;

    // enqueue the kernel command for execution
    clEnqueueNDRangeKernel(command_queue, kernel, 1, NULL, &global, NULL, 0, NULL, NULL);
    clFinish(command_queue);

    // copy the results from out of the output buffer
    clEnqueueReadBuffer(command_queue, output, CL_TRUE, 0, sizeof(char) * DATA_SIZE, results, 0, NULL, NULL);

    // print the results
    printf("output: ");
    // for(i=0;i<DATA_SIZE; i++)
    // {
         printf("%s ",results);
    // }

    // cleanup - release OpenCL resources
    clReleaseMemObject(input);
    clReleaseMemObject(output);
    clReleaseProgram(program);
    clReleaseKernel(kernel);
    clReleaseCommandQueue(command_queue);
    clReleaseContext(context);

    printf("\n");

    return 0;
}

tolower.cl

__kernel void vector_add(__global char *A, __global char *B)
{
  int i = get_global_id(0);
  B[i] = A[i]+32;
}