branch-pre

gistfile1.cpp

#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;

    std::sort(data, data + arraySize); //排序这行不注释掉下面的for循环会快得多

    // 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) {
            if (data[c] >= 128)
                sum += data[c];
        }
    }

    double elapsedTime = static_cast<double>(clock() - start) / CLOCKS_PER_SEC;
    std::cout << elapsedTime << std::endl;
    std::cout << "sum = " << sum << std::endl;
}