c - 高值段错误 (Xeon Phi)

Question

我正在通过 Stampede 使用 Xeon Phi 解决 Collat​​z 猜想问题。我已经测试过我的代码，对于高达 100,000 的值可以正常工作，但是测试高达 100 万的值时，我几乎立即收到段错误(“SIGSEV”)。我已经把头撞在墙上好几天了，但就是无法找出这个错误。非常感谢任何帮助。

typedef unsigned long long bigInt;

// Number to test to (starting from 1)
   #define bigSize     100000

typedef struct {
    int numSteps;
    bigInt stopPoint;
} batcher;

typedef struct {
    bigInt num;
    batcher to_batch;
} to_ret;
int main () {
    //Stores values as [num][#steps to smaller val][smaller val]
    to_ret retlist[bigSize];
    //Stores values as [#steps to smaller val][smaller val], sorted by num
    batcher results[bigSize];
    ...

    #pragma offload target(mic:0) inout(retlist) shared(retlist)
    {
        #pragma omp parallel for
        for(i = 1; i < bigSize; i++){
            retlist[i].num = i + 1;
            bigInt next = retlist[i].num;
            int count = 0;

            do {
                count++;

                if (next%2 == 1)
                    next=(3*next+1)/2;
                else
                    next/=2;

            } while(next > retlist[i].num);

            retlist[i].to_batch.numSteps = count;
            retlist[i].to_batch.stopPoint = next;
        }
    }

    ///Organizes data into a sorted array
    #pragma omp parallel for
    for (i = 0; i < bigSize; i++){
        results[retlist[i].num - 1] = retlist[i].to_batch;
    }
    ...
}

我非常有信心问题出在上面代码段的某个地方。

Answer 1

以下代码可以正确编译:

• 不会溢出堆栈
• 不会用一堆结构的 typedef 来混淆代码

• 不隐藏 bigNum 是一个 unsigned long long int。

• 确实包含索引变量“i”的声明

我无法访问优化编译指示，因此暂时将它们注释掉。

//typedef unsigned long long bigInt;

// Number to test to (starting from 1)
#define bigSize     (100000)

struct batcher
{
    int numSteps;
    //bigInt stopPoint;
    unsigned long long stopPoint;
};

struct to_ret
{
    //bigInt num;
    unsigned long long num;
    struct batcher to_batch;
};

//Stores values as [num][#steps to smaller val][smaller val]
static struct to_ret retlist[bigSize];
//Stores values as [#steps to smaller val][smaller val], sorted by num
static struct batcher results[bigSize];

int main ()
{
    int i;
    // more code here

    ////#pragma offload target(mic:0) inout(retlist) shared(retlist)
    {
        ////#pragma omp parallel for
        for(i = 1; i < bigSize; i++)
        {
            retlist[i].num = i + 1;
            //bigInt next = retlist[i].num;
            unsigned long long next = retlist[i].num;
            int count = 0;

            do
            {
                count++;

                if (next%2 == 1)
                    next=(3*next+1)/2;
                else
                    next/=2;

            } while(next > retlist[i].num);

            retlist[i].to_batch.numSteps = count;
            retlist[i].to_batch.stopPoint = next;
        }
    }

    ///Organizes data into a sorted array
    ////#pragma omp parallel for
    for (i = 0; i < bigSize; i++){
        results[retlist[i].num - 1] = retlist[i].to_batch;
    }
    // more code here

    return(0);
} // end function: main