NVIDIA-GPU-Bootcamp-Training/hpc/openacc/English/C/source_code/lab1/solutions/laplace2d.kernels.c

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#include <math.h>
#include <stdlib.h>

#define OFFSET(x, y, m) (((x)*(m)) + (y))

void initialize(double *restrict A, double *restrict Anew, int m, int n)
{
    memset(A, 0, n * m * sizeof(double));
    memset(Anew, 0, n * m * sizeof(double));

    for(int i = 0; i < m; i++){
        A[i] = 1.0;
        Anew[i] = 1.0;
    }
}

double calcNext(double *restrict A, double *restrict Anew, int m, int n)
{
    double error = 0.0;
#pragma acc kernels
#pragma acc loop independent reduction(max:error)
    for( int j = 1; j < n-1; j++)
    {
        for( int i = 1; i < m-1; i++ )
        {
            Anew[OFFSET(j, i, m)] = 0.25 * ( A[OFFSET(j, i+1, m)] + A[OFFSET(j, i-1, m)]
                                           + A[OFFSET(j-1, i, m)] + A[OFFSET(j+1, i, m)]);
            error = fmax( error, fabs(Anew[OFFSET(j, i, m)] - A[OFFSET(j, i , m)]));
        }
    }
    return error;
}
        
void swap(double *restrict A, double *restrict Anew, int m, int n)
{
#pragma acc kernels
#pragma acc loop independent
    for( int j = 1; j < n-1; j++)
    {
        for( int i = 1; i < m-1; i++ )
        {
            A[OFFSET(j, i, m)] = Anew[OFFSET(j, i, m)];    
        }
    }
}

void deallocate(double *restrict A, double *restrict Anew)
{
    free(A);
    free(Anew);
}