/* -*- Mode: C; c-basic-offset:4 ; -*- */
/*
 *
 *  (C) 2001 by Argonne National Laboratory.
 *      See COPYRIGHT in top-level directory.
 */

#include "mpiimpl.h"
#include "group.h"

/* -- Begin Profiling Symbol Block for routine MPI_Group_difference */
#if defined(HAVE_PRAGMA_WEAK)
#pragma weak MPI_Group_difference = PMPI_Group_difference
#elif defined(HAVE_PRAGMA_HP_SEC_DEF)
#pragma _HP_SECONDARY_DEF PMPI_Group_difference  MPI_Group_difference
#elif defined(HAVE_PRAGMA_CRI_DUP)
#pragma _CRI duplicate MPI_Group_difference as PMPI_Group_difference
#endif
/* -- End Profiling Symbol Block */

/* Define MPICH_MPI_FROM_PMPI if weak symbols are not supported to build
   the MPI routines */
#ifndef MPICH_MPI_FROM_PMPI
#undef MPI_Group_difference
#define MPI_Group_difference PMPI_Group_difference

#endif

#undef FUNCNAME
#define FUNCNAME MPI_Group_difference

/*@

MPI_Group_difference - Makes a group from the difference of two groups

Input Parameters:
+ group1 - first group (handle) 
- group2 - second group (handle) 

Output Parameter:
. newgroup - difference group (handle) 

Notes:
The generated group containc the members of 'group1' that are not in 'group2'.

.N ThreadSafe

.N Fortran

.N Errors
.N MPI_SUCCESS
.N MPI_ERR_GROUP
.N MPI_ERR_EXHAUSTED

.seealso: MPI_Group_free
@*/
int MPI_Group_difference(MPI_Group group1, MPI_Group group2, MPI_Group *newgroup)
{
    static const char FCNAME[] = "MPI_Group_difference";
    int mpi_errno = MPI_SUCCESS;
    MPID_Group *group_ptr1 = NULL;
    MPID_Group *group_ptr2 = NULL;
    MPID_Group *new_group_ptr;
    int size1, size2, i, k, g1_idx, g2_idx, l1_pid, l2_pid, nnew;
    MPID_MPI_STATE_DECL(MPID_STATE_MPI_GROUP_DIFFERENCE);

    MPIR_ERRTEST_INITIALIZED_ORDIE();
    
    MPIU_THREAD_SINGLE_CS_ENTER("group");
    MPID_MPI_FUNC_ENTER(MPID_STATE_MPI_GROUP_DIFFERENCE);

    /* Validate parameters, especially handles needing to be converted */
#   ifdef HAVE_ERROR_CHECKING
    {
        MPID_BEGIN_ERROR_CHECKS;
        {
	    MPIR_ERRTEST_GROUP(group1, mpi_errno);
	    MPIR_ERRTEST_GROUP(group2, mpi_errno);
            if (mpi_errno != MPI_SUCCESS) goto fn_fail;
        }
        MPID_END_ERROR_CHECKS;
    }
#   endif
    
    /* Convert MPI object handles to object pointers */
    MPID_Group_get_ptr( group1, group_ptr1 );
    MPID_Group_get_ptr( group2, group_ptr2 );

    /* Validate parameters and objects (post conversion) */
#   ifdef HAVE_ERROR_CHECKING
    {
        MPID_BEGIN_ERROR_CHECKS;
        {
            /* Validate group_ptr */
            MPID_Group_valid_ptr( group_ptr1, mpi_errno );
            MPID_Group_valid_ptr( group_ptr2, mpi_errno );
	    /* If either group_ptr is not valid, it will be reset to null */
            if (mpi_errno) goto fn_fail;
        }
        MPID_END_ERROR_CHECKS;
    }
#   endif /* HAVE_ERROR_CHECKING */

    /* ... body of routine ...  */
    
    /* Return a group consisting of the members of group1 that are *not*
       in group2 */
    size1 = group_ptr1->size;
    size2 = group_ptr2->size;
    /* Insure that the lpid lists are setup */
    MPIR_Group_setup_lpid_pairs( group_ptr1, group_ptr2 );

    for (i=0; i<size1; i++) {
	group_ptr1->lrank_to_lpid[i].flag = 0;
    }
    g1_idx = group_ptr1->idx_of_first_lpid;
    g2_idx = group_ptr2->idx_of_first_lpid;
    
    nnew = size1;
    while (g1_idx >= 0 && g2_idx >= 0) {
	l1_pid = group_ptr1->lrank_to_lpid[g1_idx].lpid;
	l2_pid = group_ptr2->lrank_to_lpid[g2_idx].lpid;
	if (l1_pid < l2_pid) {
	    g1_idx = group_ptr1->lrank_to_lpid[g1_idx].next_lpid;
	}
	else if (l1_pid > l2_pid) {
	    g2_idx = group_ptr2->lrank_to_lpid[g2_idx].next_lpid;
	}
	else {
	    /* Equal */
	    group_ptr1->lrank_to_lpid[g1_idx].flag = 1;
	    g1_idx = group_ptr1->lrank_to_lpid[g1_idx].next_lpid;
	    g2_idx = group_ptr2->lrank_to_lpid[g2_idx].next_lpid;
	    nnew --;
	}
    }
    /* Create the group */
    if (nnew == 0) {
	/* See 5.3.2, Group Constructors.  For many group routines,
	   the standard explicitly says to return MPI_GROUP_EMPTY; 
	   for others it is implied */
	*newgroup = MPI_GROUP_EMPTY;
	goto fn_exit;
    }
    else {
	mpi_errno = MPIR_Group_create( nnew, &new_group_ptr );
	/* --BEGIN ERROR HANDLING-- */
	if (mpi_errno) {
	    goto fn_fail;
	}
	/* --END ERROR HANDLING-- */
	new_group_ptr->rank = MPI_UNDEFINED;
	k = 0;
	for (i=0; i<size1; i++) {
	    if (!group_ptr1->lrank_to_lpid[i].flag) {
		new_group_ptr->lrank_to_lpid[k].lrank = k;
		new_group_ptr->lrank_to_lpid[k].lpid = 
		    group_ptr1->lrank_to_lpid[i].lpid;
		if (i == group_ptr1->rank) 
		    new_group_ptr->rank = k;
		k++;
	    }
	}
    }

    *newgroup = new_group_ptr->handle;

    /* ... end of body of routine ... */

  fn_exit:
    MPID_MPI_FUNC_EXIT(MPID_STATE_MPI_GROUP_DIFFERENCE);
    MPIU_THREAD_SINGLE_CS_EXIT("group");
    return mpi_errno;

  fn_fail:
    /* --BEGIN ERROR HANDLING-- */
#   ifdef HAVE_ERROR_CHECKING
    {
	mpi_errno = MPIR_Err_create_code(
	    mpi_errno, MPIR_ERR_RECOVERABLE, FCNAME, __LINE__, MPI_ERR_OTHER, "**mpi_group_difference",
	    "**mpi_group_difference %G %G %p", group1, group2, newgroup);
    }
#   endif
    mpi_errno = MPIR_Err_return_comm( NULL, FCNAME, mpi_errno );
    goto fn_exit;
    /* --END ERROR HANDLING-- */
}
