thrust/dependencies/cub/examples/device/example_device_select_if.cu

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/******************************************************************************
 * Simple example of DeviceSelect::If().
 *
 * Selects items from from a sequence of int keys using a
 * section functor (greater-than)
 *
 * To compile using the command line:
 *   nvcc -arch=sm_XX example_device_select_if.cu -I../.. -lcudart -O3
 *
 ******************************************************************************/

// Ensure printing of CUDA runtime errors to console
#define CUB_STDERR

#include <stdio.h>

#include <cub/util_allocator.cuh>
#include <cub/device/device_select.cuh>

#include "../../test/test_util.h"

using namespace cub;


//---------------------------------------------------------------------
// Globals, constants and typedefs
//---------------------------------------------------------------------

bool                    g_verbose = false;  // Whether to display input/output to console
CachingDeviceAllocator  g_allocator(true);  // Caching allocator for device memory


/// Selection functor type
struct GreaterThan
{
    int compare;

    __host__ __device__ __forceinline__
    GreaterThan(int compare) : compare(compare) {}

    __host__ __device__ __forceinline__
    bool operator()(const int &a) const {
        return (a > compare);
    }
};


//---------------------------------------------------------------------
// Test generation
//---------------------------------------------------------------------

/**
 * Initialize problem, setting runs of random length chosen from [1..max_segment]
 */
void Initialize(
    int     *h_in,
    int     num_items,
    int     max_segment)
{
    int key = 0;
    int i = 0;
    while (i < num_items)
    {
        // Randomly select number of repeating occurrences uniformly from [1..max_segment]
        unsigned short max_short = (unsigned short) -1;
        unsigned short repeat;
        RandomBits(repeat);
        repeat = (unsigned short) ((float(repeat) * (float(max_segment) / float(max_short))));
        repeat = CUB_MAX(1, repeat);

        int j = i;
        while (j < CUB_MIN(i + repeat, num_items))
        {
            h_in[j] = key;
            j++;
        }

        i = j;
        key++;
    }

    if (g_verbose)
    {
        printf("Input:\n");
        DisplayResults(h_in, num_items);
        printf("\n\n");
    }
}


/**
 * Solve unique problem
 */
template <typename SelectOp>
int Solve(
    int             *h_in,
    SelectOp        select_op,
    int             *h_reference,
    int             num_items)
{
    int num_selected = 0;
    for (int i = 0; i < num_items; ++i)
    {
        if (select_op(h_in[i]))
        {
            h_reference[num_selected] = h_in[i];
            num_selected++;
        }
        else
        {
            h_reference[num_items - (i - num_selected) - 1] = h_in[i];
        }
    }

    return num_selected;
}


//---------------------------------------------------------------------
// Main
//---------------------------------------------------------------------

/**
 * Main
 */
int main(int argc, char** argv)
{
    int num_items           = 150;
    int max_segment         = 40;       // Maximum segment length

    // Initialize command line
    CommandLineArgs args(argc, argv);
    g_verbose = args.CheckCmdLineFlag("v");
    args.GetCmdLineArgument("n", num_items);
    args.GetCmdLineArgument("maxseg", max_segment);

    // Print usage
    if (args.CheckCmdLineFlag("help"))
    {
        printf("%s "
            "[--n=<input items> "
            "[--device=<device-id>] "
            "[--maxseg=<max segment length>]"
            "[--v] "
            "\n", argv[0]);
        exit(0);
    }

    // Initialize device
    CubDebugExit(args.DeviceInit());

    // Allocate host arrays
    int *h_in        = new int[num_items];
    int *h_reference = new int[num_items];

    // Select a pivot index
    unsigned int pivot_index;
    unsigned int max_int = (unsigned int) -1;
    RandomBits(pivot_index);
    pivot_index = (unsigned int) ((float(pivot_index) * (float(num_items - 1) / float(max_int))));
    printf("Pivot idx: %d\n", pivot_index); fflush(stdout);

    // Initialize problem and solution
    Initialize(h_in, num_items, max_segment);
    GreaterThan select_op(h_in[pivot_index]);

    int num_selected = Solve(h_in, select_op, h_reference, num_items);

    printf("cub::DeviceSelect::If %d items, %d selected (avg run length %d), %d-byte elements\n",
        num_items, num_selected, (num_selected > 0) ? num_items / num_selected : 0, (int) sizeof(int));
    fflush(stdout);

    // Allocate problem device arrays
    int *d_in = NULL;
    CubDebugExit(g_allocator.DeviceAllocate((void**)&d_in, sizeof(int) * num_items));

    // Initialize device input
    CubDebugExit(cudaMemcpy(d_in, h_in, sizeof(int) * num_items, cudaMemcpyHostToDevice));

    // Allocate device output array and num selected
    int     *d_out            = NULL;
    int     *d_num_selected_out   = NULL;
    CubDebugExit(g_allocator.DeviceAllocate((void**)&d_out, sizeof(int) * num_items));
    CubDebugExit(g_allocator.DeviceAllocate((void**)&d_num_selected_out, sizeof(int)));

    // Allocate temporary storage
    void            *d_temp_storage = NULL;
    size_t          temp_storage_bytes = 0;
    CubDebugExit(DeviceSelect::If(d_temp_storage, temp_storage_bytes, d_in, d_out, d_num_selected_out, num_items, select_op));
    CubDebugExit(g_allocator.DeviceAllocate(&d_temp_storage, temp_storage_bytes));

    // Run
    CubDebugExit(DeviceSelect::If(d_temp_storage, temp_storage_bytes, d_in, d_out, d_num_selected_out, num_items, select_op));

    // Check for correctness (and display results, if specified)
    int compare = CompareDeviceResults(h_reference, d_out, num_selected, true, g_verbose);
    printf("\t Data %s ", compare ? "FAIL" : "PASS");
    compare = compare | CompareDeviceResults(&num_selected, d_num_selected_out, 1, true, g_verbose);
    printf("\t Count %s ", compare ? "FAIL" : "PASS");
    AssertEquals(0, compare);

    // Cleanup
    if (h_in) delete[] h_in;
    if (h_reference) delete[] h_reference;
    if (d_in) CubDebugExit(g_allocator.DeviceFree(d_in));
    if (d_out) CubDebugExit(g_allocator.DeviceFree(d_out));
    if (d_num_selected_out) CubDebugExit(g_allocator.DeviceFree(d_num_selected_out));
    if (d_temp_storage) CubDebugExit(g_allocator.DeviceFree(d_temp_storage));

    printf("\n\n");

    return 0;
}