output.txt

=== -std=C++98, -Os ======
6.393718s wall, 1.480000s user + 4.110000s system = 5.590000s CPU (87.4%)
6.441048s wall, 2.010000s user + 3.770000s system = 5.780000s CPU (89.7%)
24.594495s wall, 5.680000s user + 13.500000s system = 19.180000s CPU (78.0%)
23.071802s wall, 5.590000s user + 12.920000s system = 18.510000s CPU (80.2%)

=== -std=C++11, -Os ======
6.956083s wall, 1.510000s user + 4.330000s system = 5.840000s CPU (84.0%)
6.532527s wall, 2.030000s user + 3.820000s system = 5.850000s CPU (89.6%)
11.977692s wall, 4.160000s user + 5.210000s system = 9.370000s CPU (78.2%)
13.777258s wall, 4.620000s user + 5.380000s system = 10.000000s CPU (72.6%)

valarray_apply_copy_cost.cpp

#include <valarray>
#include <boost/timer/timer.hpp>

namespace {
    float generator(float in)
    {
        return in + 1.0f;
    }
}

int main(void)
{
    const size_t LENGTH = 10e8;
    {
        std::valarray<float> target(0.0f, LENGTH);
        {
            boost::timer::auto_cpu_timer timer;
            for (float* iter = &target[0]; iter != &target[0] + LENGTH; ++iter) {
                *iter = generator(*iter);
            }
        }
    }
    {
        std::valarray<float> target(0.0f, LENGTH);
        {
            boost::timer::auto_cpu_timer timer;
            target += 1.0f;
        }
    }
    {
        std::valarray<float> target(0.0f, LENGTH);
        {
            boost::timer::auto_cpu_timer timer;
            target = target.apply(generator);
        }
    }
    {
        std::valarray<float> target(0.0f, LENGTH);
        std::valarray<float> target_copy(0.0f, LENGTH);
        {
            boost::timer::auto_cpu_timer timer;
            target_copy = target.apply(generator);
        }
    }
    return 0;
}