/* test program that writes integers to files 
   each process write NUM_ELEMENTS integers NUM_BLOCKS times
   The output file must contain integers from 0 -> NUM_BLOCKS*NUM_ELEMENTS*num_processes - 1
*/
#include <mpi.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/uio.h>
#include <string.h>

#define NUM_BLOCKS 4 /* how many blocks each process will write */
#define NUM_ELEMENTS 4 /* number of elements each process will write in a block */

int main(int argc, char** argv)
{

    MPI_File fh;
    int size, rank, i, j, k, h;
    MPI_Datatype ftype,newtype;
    int buf_write[NUM_BLOCKS*NUM_ELEMENTS];
    int buf_read[NUM_BLOCKS*NUM_ELEMENTS];
    MPI_Aint disp[NUM_BLOCKS+1], d[3];
    int blocklength[NUM_BLOCKS+1], b[3];
    MPI_Datatype types[NUM_BLOCKS+1], t[3];
    int datsize;
    int SIZE = NUM_BLOCKS * NUM_ELEMENTS;
    MPI_Status status;

    MPI_Init (&argc, &argv);

    MPI_Comm_size (MPI_COMM_WORLD, &size);
    MPI_Comm_rank (MPI_COMM_WORLD, &rank);

    k=0;
    for (i=0; i<NUM_BLOCKS ; i++)
    {
        for (j=0 ; j<NUM_ELEMENTS ; j++)
        {
            buf_write[k++] = rank*NUM_ELEMENTS + j + i*size*NUM_ELEMENTS;
        }
    }

    MPI_Type_size(MPI_INT, &datsize);

    for (i=0 ; i<NUM_BLOCKS ; i++)
    {
        disp[i] = (rank + i*size) * NUM_ELEMENTS * datsize;
        blocklength[i] = NUM_ELEMENTS;
	types[i] = MPI_INT;
    }
    blocklength[NUM_BLOCKS] = 1;
    disp[NUM_BLOCKS] = NUM_BLOCKS*NUM_ELEMENTS*size*datsize;
    types[NUM_BLOCKS] = MPI_UB;
    
        for (i=0 ; i<=NUM_BLOCKS ; i++) {
            printf ("%d: displ[%d] = %d\n",rank,i,disp[i]);
        }

    MPI_Type_struct (NUM_BLOCKS+1, blocklength, disp, types, &ftype);
    MPI_Type_commit (&ftype);

    MPI_File_open (MPI_COMM_WORLD, argv[1], MPI_MODE_WRONLY | MPI_MODE_CREATE,
                   MPI_INFO_NULL, &fh);
    if (NULL == fh)
    {
        printf("Can't open file: %s\n",argv[1]);
        exit(1);
    }

    MPI_File_set_view(fh, 0, MPI_INT, ftype, "native", MPI_INFO_NULL);

    MPI_File_write_at_all (fh, 
                           16, 
                           buf_write, 
                           NUM_BLOCKS*NUM_ELEMENTS, 
                           MPI_INT, 
                           MPI_STATUS_IGNORE);
    
    MPI_File_close(&fh);

    MPI_Type_free (&ftype);
    MPI_Finalize ();
    
    return 0;
}