Question

我正在尝试学习OpenCL基础知识。

我在内核中想到了这段代码：

out[ 1 & ((a+b)==(b+a)) ] = (char)1;

会产生与以下相同的结果：

out[ 1 ] = (char)1;

有人能告诉我为什么会产生不同的结果吗？

以下是我内核的完整源代码：

#pragma OPENCL EXTENSION cl_khr_byte_addressable_store : enable
__kernel void hello(__global char * out)
{
    size_t tid = get_global_id(0);
    int a = tid & 0xff;
    int b = (tid >> 8) & 0xff;
    out[ 1 & ((a+b)==(b+a)) ] = (char)1;
}

如果我用“out [1] =（char）1”替换最后一个语句;“那么“out [0]”将不会被写入。但上面的内核会将“1”写入out [0]。

编辑：这是我的C ++代码：

#include <utility>
#define __NO_STD_VECTOR // Use cl::vector instead of STL version
#include <CL/cl.hpp>

#include <cstdio>
#include <cstdlib>
#include <fstream>
#include <iostream>
#include <string>
#include <iterator>

inline void checkErr(cl_int err, const char * name)
{
    if (err != CL_SUCCESS) {
        std::cerr << "ERROR: " << name
                 << " (" << err << ")" << std::endl;
        std::exit(EXIT_FAILURE);
    }
}

int main()
{
    cl_int err;

    cl::vector< cl::Platform > platformList;
    cl::Platform::get(&platformList);
    checkErr(platformList.size()!=0 ? CL_SUCCESS : -1, "cl::Platform::get");
    std::cerr << "Platform number is: " << platformList.size() << std::endl;

    std::string platformVendor;
    platformList[0].getInfo((cl_platform_info)CL_PLATFORM_VENDOR, &platformVendor);
    std::cerr << "Platform is by: " << platformVendor << "\n";
    cl_context_properties cprops[3] = 
        {CL_CONTEXT_PLATFORM, (cl_context_properties)(platformList[0])(), 0};

    cl::Context context(
       CL_DEVICE_TYPE_GPU, 
       cprops,
       NULL,
       NULL,
       &err);
    checkErr(err, "Conext::Context()"); 


    unsigned char outH[2] = {0};
    cl::Buffer outCL(
        context,
        CL_MEM_WRITE_ONLY | CL_MEM_USE_HOST_PTR,
        sizeof(outH),
        outH,
        &err);
    checkErr(err, "Buffer::Buffer()");


    cl::vector<cl::Device> devices;
    devices = context.getInfo<CL_CONTEXT_DEVICES>();
    checkErr(
        devices.size() > 0 ? CL_SUCCESS : -1, "devices.size() > 0");


    std::ifstream file("condition1.cl");
    checkErr(file.is_open() ? CL_SUCCESS:-1, "condition1.cl");
    const std::string prog(std::istreambuf_iterator<char>(file), (std::istreambuf_iterator<char>()));

    cl::Program::Sources source(1, std::make_pair(prog.c_str(), prog.length()+1));
    cl::Program program(context, source);
    err = program.build(devices,""); 
    checkErr(err, "Program::build()"); 


    cl::Kernel kernel(program, "hello", &err);
    checkErr(err, "Kernel::Kernel()");

    err = kernel.setArg(0, outCL);
    checkErr(err, "Kernel::setArg()");


    cl::CommandQueue queue(context, devices[0], 0, &err);
    checkErr(err, "CommandQueue::CommandQueue()");


    cl::Event event;
    err = queue.enqueueNDRangeKernel(
        kernel, 
        cl::NullRange,
        cl::NDRange(65536),
         cl::NDRange(1, 1), 
        NULL, 
        &event);
    checkErr(err, "ComamndQueue::enqueueNDRangeKernel()");

    event.wait();    
    err = queue.enqueueReadBuffer(
        outCL,
        CL_TRUE,
        0,
        sizeof(outH),
        outH);
    checkErr(err, "ComamndQueue::enqueueReadBuffer()");

    for (int i = 0; i < sizeof(outH); i++)
        std::cout << (int)outH[i] << " ";

    std::string str;
    std::getline(std::cin, str);

    return EXIT_SUCCESS;
}

EDIT2：

至少不是由“未定义的行为”引起的。我也得到了这个内核代码的奇怪结果：

char result = 0;
for (int a = 0; a < 2; a++) {
    for (int b = 0; b < 2; b++) {
        if ((a+b) != (b+a))
            result |= (1 << (a+2*b));
    }
}

我希望“result”得到值0.但它得到值6.如果我将！=更改为==那么结果得到值9.所以在这段代码中，当“a”是不等于“b”，则（a + b）不等于（b + a）。

如果我更改代码并为“a”或“b”设置已知值，则结果将为0，如我所料。例如：

char result = 0;
int a = 1;
/*for (int a = 0; a < 2; a++)*/ {
    for (int b = 0; b < 2; b++) {
        if ((a+b) != (b+a))
            result |= (1 << (a+2*b));
    }
}

OpenCL输出缓冲区

0 个答案: