/* grader.c - Let's experiment with creating our own data type.
 */
#include <mpi.h>
#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#define SIZE 12

struct grade
{
  int number;
  char letter;
};

// I'm passing my rank so I can print out who is doing what.
void assign_letter(struct grade student[], int num_students, int my_rank)
{
  int i, percent;
  char letter;

  for (i = 0; i < num_students; ++i)
  {
    percent = student[i].number;
    if (percent >= 90)
      letter = 'A';
    else if (percent >= 80)
      letter = 'B';
    else if (percent >= 70)
      letter = 'C';
    else if (percent >= 60)
      letter = 'D';
    else
      letter = 'F';
    student[i].letter = letter;
    printf("Process %d determines that %d is a %c.\n", my_rank, percent, letter);
  }
}

int main()
{
  struct grade class[SIZE], *local_list;
  MPI_Datatype new_type;
  int my_rank, num_processes, i, local_size, name_length;
  int block_length[] = {1, 1};
  int displacement[] = {0, 4};
  int type[] = {MPI_INT, MPI_CHAR};
  char processor_name[MPI_MAX_PROCESSOR_NAME];

  MPI_Init(NULL, NULL);
  MPI_Comm_size(MPI_COMM_WORLD, &num_processes);
  MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
  MPI_Get_processor_name(processor_name, &name_length);
  MPI_Type_create_struct(2, block_length, displacement, type, &new_type);
  MPI_Type_commit(&new_type);

  // Let's have the main node set the numerical grades randomly.
  if (my_rank == 0)
  {
    srand (time (NULL));
    for (i = 0; i < SIZE; ++i)
      class[i].number = 50 + rand() % 50;
  }

  // Let's share the work of determining letter grades.
  // See p. 111 for format of scatter function.
  local_size = SIZE / num_processes;
  local_list = (struct grade *) malloc (sizeof(struct grade) * local_size);
  MPI_Scatter(class, local_size, new_type, local_list, local_size, new_type,
              0, MPI_COMM_WORLD);

  assign_letter(local_list, local_size, my_rank);
  MPI_Gather(local_list, local_size, new_type, class, local_size, new_type,
             0, MPI_COMM_WORLD);

  // Output
  if (my_rank == 0)
    for (i = 0; i < SIZE; ++i)
      printf("%2d %c\n", class[i].number, class[i].letter);

  MPI_Type_free(&new_type);
  MPI_Finalize();
  return 0;
}
/* Output:
Process 0 determines that 75 is a C.
Process 2 determines that 72 is a C.
Process 2 determines that 93 is a A.
Process 2 determines that 72 is a C.
Process 0 determines that 58 is a F.
Process 2 determines that 92 is a A.
Process 1 determines that 77 is a C.
Process 0 determines that 93 is a A.
Process 0 determines that 90 is a A.
Process 1 determines that 58 is a F.
Process 1 determines that 94 is a A.
Process 1 determines that 86 is a B.
75 C
58 F
93 A
90 A
77 C
58 F
94 A
86 B
72 C
93 A
72 C
92 A
*/