相关疑难解决方法(0)

这是一段看似非常特殊的C++代码.出于某种奇怪的原因,奇迹般地对数据进行排序使得代码几乎快了六倍.

#include <algorithm>
#include <ctime>
#include <iostream>

int main()
{
    // Generate data
    const unsigned arraySize = 32768;
    int data[arraySize];

    for (unsigned c = 0; c < arraySize; ++c)
        data[c] = std::rand() % 256;

    // !!! With this, the next loop runs faster.
    std::sort(data, data + arraySize);

    // Test
    clock_t start = clock();
    long long sum = 0;

    for (unsigned i = 0; i < 100000; ++i)
    {
        // Primary loop
        for (unsigned c = 0; c < arraySize; ++c) …

我听说有英特尔在线书籍描述了特定汇编指令所需的CPU周期,但我无法找到它(经过努力).有人能告诉我如何找到CPU周期吗？

下面是一个例子,在下面的代码中,mov/lock是1个CPU周期,xchg是3个CPU周期.

// This part is Platform dependent!
#ifdef WIN32
inline int CPP_SpinLock::TestAndSet(int* pTargetAddress, 
                                              int nValue)
{
    __asm
    {
        mov edx, dword ptr [pTargetAddress]
        mov eax, nValue
        lock xchg eax, dword ptr [edx]
    }
    // mov = 1 CPU cycle
    // lock = 1 CPU cycle
    // xchg = 3 CPU cycles
}

#endif // WIN32

顺便说一句:这是我发布的代码的URL:http://www.codeproject.com/KB/threads/spinlocks.aspx