Prev

Next

Index-> contents reference index search external

Up-> CppAD multi_thread thread_test.cpp a11c_openmp.cpp

a11c_openmp.cpp

Headings-> Purpose Source Code

# include <omp.h>
# include <limits>
# include <cmath>
# include <cassert>
// for size_t
# include <cstddef>
//
# define NUMBER_THREADS 4

namespace {
    // Beginning of Example A.1.1.1c of OpenMP 2.5 standard document ---------
    void a1(int n, float *a, float *b)
    {   // Original had 'int i;' instead of 'int i = 0;'
        // Silence warning by clang 9.0.0: variable 'i' is uninitialized.
        int i = 0;
    # pragma omp parallel for
        for(i = 1; i < n; i++) /* i is private by default */
        {   assert( omp_get_num_threads() == NUMBER_THREADS );
            b[i] = (a[i] + a[i-1]) / float(2);
        }
    }
    // End of Example A.1.1.1c of OpenMP 2.5 standard document ---------------
}
bool a11c(void)
{   bool ok = true;

    // Test setup
    size_t i, n = 1000;
    float *a = new float[n];
    float *b = new float[n];
    for(i = 0; i < n; i++)
        a[i] = float(i);

    int n_thread = NUMBER_THREADS;   // number of threads in parallel regions
    omp_set_dynamic(0);              // off dynamic thread adjust
    omp_set_num_threads(n_thread);   // set the number of threads

    a1(int(n), a, b);

    // check the result
    float eps = float(100) * std::numeric_limits<float>::epsilon();
    for(i = 1; i < n ; i++)
        ok &= std::fabs( (float(2) * b[i] - a[i] - a[i-1]) / b[i] ) <= eps;

    delete [] a;
    delete [] b;

    return ok;
}