//

// File:       hello.c

//

// Abstract:   A simple "Hello World" compute example showing basic usage of OpenCL which

//             calculates the mathematical square (X[i] = pow(X[i],2)) for a buffer of

//             floating point values.

//             

//

// Version:    <1.0>

//

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// Copyright ( C ) 2008 Apple Inc. All Rights Reserved.

//

////////////////////////////////////////////////////////////////////////////////

#include <fcntl.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <math.h>

#include <unistd.h>

#include <sys/types.h>

#include <sys/stat.h>

#include <OpenCL/opencl.h>

////////////////////////////////////////////////////////////////////////////////

// Use a static data size for simplicity

//

#define DATA_SIZE (1024)

////////////////////////////////////////////////////////////////////////////////

// Simple compute kernel which computes the square of an input array 

//

const char *KernelSource = "\n" \

"__kernel void square(                                                       \n" \

"   __global float* input,                                              \n" \

"   __global float* output,                                             \n" \

"   const unsigned int count)                                           \n" \

"{                                                                      \n" \

"   int i = get_global_id(0);                                           \n" \

"   if(i < count)                                                       \n" \

"       output[i] = input[i] * input[i];                                \n" \

"}                                                                      \n" \

"\n";

////////////////////////////////////////////////////////////////////////////////

int main(int argc, char** argv)

{

    int err;                            // error code returned from api calls

    float data[DATA_SIZE];              // original data set given to device

    float results[DATA_SIZE];           // results returned from device

    unsigned int correct;               // number of correct results returned

    size_t global;                      // global domain size for our calculation

    size_t local;                       // local domain size for our calculation

    cl_device_id device_id;             // compute device id 

    cl_context context;                 // compute context

    cl_command_queue commands;          // compute command queue

    cl_program program;                 // compute program

    cl_kernel kernel;                   // compute kernel

    cl_mem input;                       // device memory used for the input array

    cl_mem output;                      // device memory used for the output array

    // Fill our data set with random float values

    //

    int i = 0;

    unsigned int count = DATA_SIZE;

    for(i = 0; i < count; i++)

        data[i] = rand() / (float)RAND_MAX;

    // Connect to a compute device

    //

    int gpu = 1;

    err = clGetDeviceIDs(NULL, gpu ? CL_DEVICE_TYPE_GPU : CL_DEVICE_TYPE_CPU, 1, &device_id, NULL);

    if (err != CL_SUCCESS)

    {

        printf("Error: Failed to create a device group!\n");

        return EXIT_FAILURE;

    }

    // Create a compute context 

    //

    context = clCreateContext(0, 1, &device_id, NULL, NULL, &err);

    if (!context)

    {

        printf("Error: Failed to create a compute context!\n");

        return EXIT_FAILURE;

    }

    // Create a command commands

    //

    commands = clCreateCommandQueue(context, device_id, 0, &err);

    if (!commands)

    {

        printf("Error: Failed to create a command commands!\n");

        return EXIT_FAILURE;

    }

    // Create the compute program from the source buffer

    //

    program = clCreateProgramWithSource(context, 1, (const char **) & KernelSource, NULL, &err);

    if (!program)

    {

        printf("Error: Failed to create compute program!\n");

        return EXIT_FAILURE;

    }

    // Build the program executable

    //

    err = clBuildProgram(program, 0, NULL, NULL, NULL, NULL);

    if (err != CL_SUCCESS)

    {

        size_t len;

        char buffer[2048];

        printf("Error: Failed to build program executable!\n");

        clGetProgramBuildInfo(program, device_id, CL_PROGRAM_BUILD_LOG, sizeof(buffer), buffer, &len);

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

        exit(1);

    }

    // Create the compute kernel in the program we wish to run

    //

    kernel = clCreateKernel(program, "square", &err);

    if (!kernel || err != CL_SUCCESS)

    {

        printf("Error: Failed to create compute kernel!\n");

        exit(1);

    }

    // Create the input and output arrays in device memory for our calculation

    //

    input = clCreateBuffer(context,  CL_MEM_READ_ONLY,  sizeof(float) * count, NULL, NULL);

    output = clCreateBuffer(context, CL_MEM_WRITE_ONLY, sizeof(float) * count, NULL, NULL);

    if (!input || !output)

    {

        printf("Error: Failed to allocate device memory!\n");

        exit(1);

    }    

    // Write our data set into the input array in device memory 

    //

    err = clEnqueueWriteBuffer(commands, input, CL_TRUE, 0, sizeof(float) * count, data, 0, NULL, NULL);

    if (err != CL_SUCCESS)

    {

        printf("Error: Failed to write to source array!\n");

        exit(1);

    }

    // Set the arguments to our compute kernel

    //

    err = 0;

    err  = clSetKernelArg(kernel, 0, sizeof(cl_mem), &input);

    err |= clSetKernelArg(kernel, 1, sizeof(cl_mem), &output);

    err |= clSetKernelArg(kernel, 2, sizeof(unsigned int), &count);

    if (err != CL_SUCCESS)

    {

        printf("Error: Failed to set kernel arguments! %d\n", err);

        exit(1);

    }

    // Get the maximum work group size for executing the kernel on the device

    //

    err = clGetKernelWorkGroupInfo(kernel, device_id, CL_KERNEL_WORK_GROUP_SIZE, sizeof(local), &local, NULL);

    if (err != CL_SUCCESS)

    {

        printf("Error: Failed to retrieve kernel work group info! %d\n", err);

        exit(1);

    }

    // Execute the kernel over the entire range of our 1d input data set

    // using the maximum number of work group items for this device

    //

    global = count;

    err = clEnqueueNDRangeKernel(commands, kernel, 1, NULL, &global, &local, 0, NULL, NULL);

    if (err)

    {

        printf("Error: Failed to execute kernel!\n");

        return EXIT_FAILURE;

    }

    // Wait for the command commands to get serviced before reading back results

    //

    clFinish(commands);

    // Read back the results from the device to verify the output

    //

    err = clEnqueueReadBuffer( commands, output, CL_TRUE, 0, sizeof(float) * count, results, 0, NULL, NULL );  

    if (err != CL_SUCCESS)

    {

        printf("Error: Failed to read output array! %d\n", err);

        exit(1);

    }

    // Validate our results

    //

    correct = 0;

    for(i = 0; i < count; i++)

    {

        if(results[i] == data[i] * data[i])

            correct++;

    }

    // Print a brief summary detailing the results

    //

    printf("Computed '%d/%d' correct values!\n", correct, count);

    // Shutdown and cleanup

    //

    clReleaseMemObject(input);

    clReleaseMemObject(output);

    clReleaseProgram(program);

    clReleaseKernel(kernel);

    clReleaseCommandQueue(commands);

    clReleaseContext(context);

    return 0;

}