gmpdemo.cpp

denormalized.cpp

/*
 * about denormalized float number
 */

#include <iostream>
#include <string>

using namespace std;

int main(int argc, char const *argv[])
{
    const float x = 1.1;
    const float z = 1.123;
    float y = x;
    for (int j = 0; j < 90000000; j++)
    {
        y *= x;
        y /= z;
        y += 0.1f;
        y -= 0.1f;
    }

    getchar();
    return 0;
}

#include <iostream>
#include <string>

using namespace std;

int main(int argc, char const *argv[])
{
    const float x = 1.1;
    const float z = 1.123;
    float y = x;
    for (int j = 0; j < 90000000; j++)
    {
        y *= x;
        y /= z;
        y += 0;
        y -= 0;
    }
    getchar();
    return 0;
}

// fixed code
#include <iostream>
#include <string>
#include <fenv.h>

using namespace std;

int main(int argc, char const *argv[])
{
    fesetenv(FE_DEL_DISABLE_SSE_DENORMS_ENV);
    const float x = 1.1;
    const float z = 1.123;
    float y = x;
    for (int j = 0; j < 90000000; j++)
    {
        y *= x;
        y /= z;
        y += 0;
        y -= 0;
    }
    getchar();
    return 0;
}

// snippet1
const float x[16] = {  1.1,   1.2,   1.3,     1.4,   1.5,   1.6,   1.7,   1.8,
                       1.9,   2.0,   2.1,     2.2,   2.3,   2.4,   2.5,   2.6
                    };
const float z[16] = {1.123, 1.234, 1.345, 156.467, 1.578, 1.689, 1.790, 1.812,
                     1.923, 2.034, 2.145,   2.256, 2.367, 2.478, 2.589, 2.690
                    };
float y[16];
for (int i = 0; i < 16; i++)
{
    y[i] = x[i];
}

for (int j = 0; j < 9000000; j++)
{
    for (int i = 0; i < 16; i++)
    {
        y[i] *= x[i];
        y[i] /= z[i];
        y[i] = y[i] + 0.1f; // <--
        y[i] = y[i] - 0.1f; // <--
    }
}

// snippet2
const float x[16] = {  1.1,   1.2,   1.3,     1.4,   1.5,   1.6,   1.7,   1.8,
                       1.9,   2.0,   2.1,     2.2,   2.3,   2.4,   2.5,   2.6
                    };
const float z[16] = {1.123, 1.234, 1.345, 156.467, 1.578, 1.689, 1.790, 1.812,
                     1.923, 2.034, 2.145,   2.256, 2.367, 2.478, 2.589, 2.690
                    };
float y[16];
for (int i = 0; i < 16; i++)
{
    y[i] = x[i];
}

for (int j = 0; j < 9000000; j++)
{
    for (int i = 0; i < 16; i++)
    {
        y[i] *= x[i];
        y[i] /= z[i];
        y[i] = y[i] + 0; // <--
        y[i] = y[i] - 0; // <--
    }
}

// snippet3
int main() {

    double start = omp_get_wtime();

    const float x[16] = {1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6};
    const float z[16] = {1.123, 1.234, 1.345, 156.467, 1.578, 1.689, 1.790, 1.812, 1.923, 2.034, 2.145, 2.256, 2.367, 2.478, 2.589, 2.690};
    float y[16];
    for (int i = 0; i < 16; i++)
    {
        y[i] = x[i];
    }
    for (int j = 0; j < 9000000; j++)
    {
        for (int i = 0; i < 16; i++)
        {
            y[i] *= x[i];
            y[i] /= z[i];
#ifdef FLOATING
            y[i] = y[i] + 0.1f;
            y[i] = y[i] - 0.1f;
#else
            y[i] = y[i] + 0;
            y[i] = y[i] - 0;
#endif

            if (j > 10000)
                cout << y[i] << "  ";
        }
        if (j > 10000)
            cout << endl;
    }

    double end = omp_get_wtime();
    cout << end - start << endl;

    system("pause");
    return 0;
}