/* -*- Mode: C; c-basic-offset:4 ; -*- */
/*
 * Copyright (c) 2004-2006 The Trustees of Indiana University and Indiana
 *                         University Research and Technology
 *                         Corporation.  All rights reserved.
 * Copyright (c) 2004-2007 The University of Tennessee and The University
 *                         of Tennessee Research Foundation.  All rights
 *                         reserved.
 * Copyright (c) 2004-2007 High Performance Computing Center Stuttgart, 
 *                         University of Stuttgart.  All rights reserved.
 * Copyright (c) 2004-2005 The Regents of the University of California.
 *                         All rights reserved.
 * Copyright (c) 2008      UT-Battelle, LLC
 * Copyright (c) 2008-2009 Cisco Systems, Inc.  All rights reserved.
 * Copyright (c) 2009      Sun Microsystems, Inc.  All rights reserved.
 * $COPYRIGHT$
 * 
 * Additional copyrights may follow
 * 
 * $HEADER$
 */
/**
 * @file
 *
 * Public interface for the MPI_Op handle.
 */

#ifndef OMPI_OP_H
#define OMPI_OP_H

#include "ompi_config.h"

#include "mpi.h"
#include "ompi/datatype/datatype.h"
#include "opal/class/opal_object.h"
#include "ompi/mpi/f77/fint_2_int.h"

#include <stdio.h>

#if defined(c_plusplus) || defined(__cplusplus)
extern "C" {
#endif

/**
 * Fortran handles; must be [manually set to be] equivalent to the
 * values in mpif.h.
 */
enum {
  OMPI_OP_FORTRAN_NULL = 0,
  /**< Corresponds to Fortran MPI_OP_NULL */
  OMPI_OP_FORTRAN_MAX,
  /**< Corresponds to Fortran MPI_MAX */
  OMPI_OP_FORTRAN_MIN,
  /**< Corresponds to Fortran MPI_MIN */
  OMPI_OP_FORTRAN_SUM,
  /**< Corresponds to Fortran MPI_SUM */
  OMPI_OP_FORTRAN_PROD,
  /**< Corresponds to Fortran MPI_PROD */
  OMPI_OP_FORTRAN_LAND,
  /**< Corresponds to Fortran MPI_LAND */
  OMPI_OP_FORTRAN_BAND,
  /**< Corresponds to Fortran MPI_BAND */
  OMPI_OP_FORTRAN_LOR,
  /**< Corresponds to Fortran MPI_LOR */
  OMPI_OP_FORTRAN_BOR,
  /**< Corresponds to Fortran MPI_BOR */
  OMPI_OP_FORTRAN_LXOR,
  /**< Corresponds to Fortran MPI_LXOR */
  OMPI_OP_FORTRAN_BXOR,
  /**< Corresponds to Fortran MPI_BXOR */
  OMPI_OP_FORTRAN_MAXLOC,
  /**< Corresponds to Fortran MPI_MAXLOC */
  OMPI_OP_FORTRAN_MINLOC,
  /**< Corresponds to Fortran MPI_MINLOC */
  OMPI_OP_FORTRAN_REPLACE,
  /**< Corresponds to Fortran MPI_REPLACE */

  OMPI_OP_FORTRAN_MAX_TYPE
  /**< Maximum value */
};

/**
 * Corresponding to the types that we can reduce over.  See
 * MPI-1:4.9.2, p114-115 and
 * MPI-2:4.15, p76-77
 */
enum {
  OMPI_OP_TYPE_UNSIGNED_CHAR,
  /**< C integer: unsigned char */
  OMPI_OP_TYPE_SIGNED_CHAR,
  /**< C integer: signed char */
  OMPI_OP_TYPE_INT,
  /**< C integer: int */
  OMPI_OP_TYPE_LONG,
  /**< C integer: long */
  OMPI_OP_TYPE_SHORT,
  /**< C integer: short */
  OMPI_OP_TYPE_UNSIGNED_SHORT,
  /**< C integer: unsigned short */
  OMPI_OP_TYPE_UNSIGNED,
  /**< C integer: unsigned */
  OMPI_OP_TYPE_UNSIGNED_LONG,
  /**< C integer: unsigned long */

  OMPI_OP_TYPE_LONG_LONG_INT,
  /**< C integer: long long int (optional) */
  OMPI_OP_TYPE_UNSIGNED_LONG_LONG,
  /**< C integer: unsigned long long (optional) */

  OMPI_OP_TYPE_INTEGER,
  /**< Fortran integer */
  OMPI_OP_TYPE_INTEGER1,
  /**< Fortran integer*1 */
  OMPI_OP_TYPE_INTEGER2,
  /**< Fortran integer*2 */
  OMPI_OP_TYPE_INTEGER4,
  /**< Fortran integer*4 */
  OMPI_OP_TYPE_INTEGER8,
  /**< Fortran integer*8 */
  OMPI_OP_TYPE_INTEGER16,
  /**< Fortran integer*16 */

  OMPI_OP_TYPE_FLOAT,
  /**< Floating point: float */
  OMPI_OP_TYPE_DOUBLE,
  /**< Floating point: double */
  OMPI_OP_TYPE_REAL,
  /**< Floating point: real */
  OMPI_OP_TYPE_REAL2,
  /**< Floating point: real*2 */
  OMPI_OP_TYPE_REAL4,
  /**< Floating point: real*4 */
  OMPI_OP_TYPE_REAL8,
  /**< Floating point: real*8 */
  OMPI_OP_TYPE_REAL16,
  /**< Floating point: real*16 */
  OMPI_OP_TYPE_DOUBLE_PRECISION,
  /**< Floating point: double precision */
  OMPI_OP_TYPE_LONG_DOUBLE,
  /**< Floating point: long double */

  OMPI_OP_TYPE_LOGICAL,
  /**< Logical */
  OMPI_OP_TYPE_BOOL,
  /**< Bool */

  OMPI_OP_TYPE_COMPLEX,
  /**< Complex */
  OMPI_OP_TYPE_DOUBLE_COMPLEX,
  /**< Double complex */
  OMPI_OP_TYPE_COMPLEX8,
  /**< Complex8 */
  OMPI_OP_TYPE_COMPLEX16,
  /**< Complex16 */
  OMPI_OP_TYPE_COMPLEX32,
  /**< Complex32 */

  OMPI_OP_TYPE_BYTE,
  /**< Byte */

  OMPI_OP_TYPE_2REAL,
  /**< 2 location Fortran: 2 real */
  OMPI_OP_TYPE_2DOUBLE_PRECISION,
  /**< 2 location Fortran: 2 double precision */
  OMPI_OP_TYPE_2INTEGER,
  /**< 2 location Fortran: 2 integer */

  OMPI_OP_TYPE_FLOAT_INT,
  /**< 2 location C: float int */
  OMPI_OP_TYPE_DOUBLE_INT,
  /**< 2 location C: double int */
  OMPI_OP_TYPE_LONG_INT,
  /**< 2 location C: long int */
  OMPI_OP_TYPE_2INT,
  /**< 2 location C: int int */
  OMPI_OP_TYPE_SHORT_INT,
  /**< 2 location C: short int */
  OMPI_OP_TYPE_LONG_DOUBLE_INT,
  /**< 2 location C: long double int */

  OMPI_OP_TYPE_WCHAR,
  /**< 2 location C: wchar_t */

  OMPI_OP_TYPE_MAX
  /**< Maximum type */
};


/**
 * Typedef for C op functions.  
 *
 * We don't use MPI_User_function because this would create a
 * confusing dependency loop between this file and mpi.h.  So this is
 * repeated code, but it's better this way (and this typedef will
 * never change, so there's not much of a maintenance worry).
 */
typedef void (ompi_op_c_handler_fn_t)(void *, void *, int *, MPI_Datatype *);

/*
 *  Three buffer ( two input and one output) function prototype
 */
typedef void (ompi_op_3buff_c_handler_fn_t)(void * restrict , void * restrict, 
        void * restrict, int *, MPI_Datatype *);


/**
 * Typedef for fortran op functions.
 */
typedef void (ompi_op_fortran_handler_fn_t)(void *, void *, 
                                            MPI_Fint *, MPI_Fint *);
/*
 * Three buffer (2 input one output) function prototype
 */
typedef void (ompi_op_3buff_fortran_handler_fn_t)(void * restrict, 
        void * restrict , void * restrict , MPI_Fint *, MPI_Fint *);


/**
 * Typedef for C++ op functions intercept.
 *
 * See the lengthy explanation for why this is different than the C
 * intercept in ompi/mpi/cxx/intercepts.cc in the
 * ompi_mpi_cxx_op_intercept() function.
 */
typedef void (ompi_op_cxx_handler_fn_t)(void *, void *, int *, 
                                        MPI_Datatype *, MPI_User_function *op);

/*
 * Three buffer (two input, one output) function prototype
 */
typedef void (ompi_op_3buff_cxx_handler_fn_t)(void * restrict, void * restrict,
        void * restrict, int *, MPI_Datatype *, MPI_User_function *op);


/*
 * Flags for MPI_Op
 */
/** Set if the MPI_Op is a built-in operation */
#define OMPI_OP_FLAGS_INTRINSIC    0x0001
/** Set if the callback function is in Fortran */
#define OMPI_OP_FLAGS_FORTRAN_FUNC 0x0002
/** Set if the callback function is in C++ */
#define OMPI_OP_FLAGS_CXX_FUNC     0x0004
/** Set if the callback function is associative (MAX and SUM will both
    have ASSOC set -- in fact, it will only *not* be set if we
    implement some extensions to MPI, because MPI says that all
    MPI_Op's should be associative, so this flag is really here for
    future expansion) */
#define OMPI_OP_FLAGS_ASSOC        0x0008
/** Set if the callback function is associative for floating point
    operands (e.g., MPI_SUM will have ASSOC set, but will *not* have
    FLOAT_ASSOC set)  */
#define OMPI_OP_FLAGS_FLOAT_ASSOC  0x0010
/** Set if the callback function is communative */
#define OMPI_OP_FLAGS_COMMUTE      0x0020


/**
 * Back-end type of MPI_Op
 */
struct ompi_op_t {
  opal_object_t super;
  /**< Parent class, for reference counting */

  char o_name[MPI_MAX_OBJECT_NAME];
  /**< Name, for debugging purposes */

  uint32_t o_flags;
  /**< Flags about the op */

  union {
      /** C handler function pointer */
      ompi_op_c_handler_fn_t *c_fn;
      /** Fortran handler function pointer */
      ompi_op_fortran_handler_fn_t *fort_fn;
      /** C++ intercept function pointer -- see lengthy comment in
          ompi/mpi/cxx/intercepts.cc::ompi_mpi_cxx_op_intercept() for
          an explanation */
      ompi_op_cxx_handler_fn_t *cxx_intercept_fn;
  } o_func[OMPI_OP_TYPE_MAX];
  /**< Array of function pointers, indexed on the operation type.  For
       non-intrinsice MPI_Op's, only the 0th element will be
       meaningful. */

  /** Index in Fortran <-> C translation array */
  int o_f_to_c_index;

  union {
      /** C handler function pointer */
      ompi_op_3buff_c_handler_fn_t *c_fn;
      /** Fortran handler function pointer */
      ompi_op_3buff_fortran_handler_fn_t *fort_fn;
      /** C++ intercept function pointer -- see lengthy comment in
          ompi/mpi/cxx/intercepts.cc::ompi_mpi_cxx_op_intercept() for
          an explanation */
      ompi_op_3buff_cxx_handler_fn_t *cxx_intercept_fn;
  } o_3buff_func[OMPI_OP_TYPE_MAX];
  /**< Array of three buffer function pointers, indexed on the operation 
    type.  For non-intrinsice MPI_Op's, only the 0th element will be
    meaningful. */
};

/**
 * Convenience typedef 
 */
typedef struct ompi_op_t ompi_op_t;
OMPI_DECLSPEC OBJ_CLASS_DECLARATION(ompi_op_t);

/**
 * Padded struct to maintain back compatibiltiy.
 * See ompi/communicator/communicator.h comments with struct ompi_communicator_t
 * for full explanation why we chose the following padding construct for predefines.
 */
#define PREDEFINED_OP_PAD (sizeof(void*) * 256)

struct ompi_predefined_op_t {
    struct ompi_op_t op;
    char padding[PREDEFINED_OP_PAD - sizeof(ompi_op_t)];
};

typedef struct ompi_predefined_op_t ompi_predefined_op_t;

/**
 * Array to map ddt->id values to the corresponding position in the op
 * function array.
 *
 * NOTE: It is possible to have an implementation without this map.
 * There are basically 3 choices for implementing "how to find the
 * right position in the op array based on the datatype":
 *
 * 1. Use the exact same ordering as ddt->id in the op map.  This is
 * nice in that it's always a direct lookup via one memory
 * de-reference.  But it makes a sparse op array, and it's at least
 * somewhat wasteful.  It also chains the ddt and op implementations
 * together.  If the ddt ever changes its ordering, op is screwed.  It
 * seemed safer from a maintenance point of view not to do it that
 * way.
 *
 * 2. Re-arrange the ddt ID values so that all the reducable types are
 * at the beginning.  This means that we can have a dense array here
 * in op, but then we have the same problem as number one -- and so
 * this didn't seem like a good idea from a maintenance point of view.
 *
 * 3. Create a mapping between the ddt->id values and the position in
 * the op array.  This allows a nice dense op array, and if we make
 * the map based on symbolic values, then if ddt ever changes its
 * ordering, it won't matter to op.  This seemed like the safest thing
 * to do from a maintenance perspective, and since it only costs one
 * extra lookup, and that lookup is way cheaper than the function call
 * to invoke the reduction operation, it seemed like the best idea.
 */
OMPI_DECLSPEC extern int ompi_op_ddt_map[DT_MAX_PREDEFINED];

/**
 * Global variable for MPI_OP_NULL
 */
OMPI_DECLSPEC extern ompi_predefined_op_t ompi_mpi_op_null;

/**
 * Global variable for MPI_MAX
 */
OMPI_DECLSPEC extern ompi_predefined_op_t ompi_mpi_op_max;

/**
 * Global variable for MPI_MIN
 */
OMPI_DECLSPEC extern ompi_predefined_op_t ompi_mpi_op_min;

/**
 * Global variable for MPI_SUM
 */
OMPI_DECLSPEC extern ompi_predefined_op_t ompi_mpi_op_sum;

/**
 * Global variable for MPI_PROD
 */
OMPI_DECLSPEC extern ompi_predefined_op_t ompi_mpi_op_prod;

/**
 * Global variable for MPI_LAND
 */
OMPI_DECLSPEC extern ompi_predefined_op_t ompi_mpi_op_land;

/**
 * Global variable for MPI_BAND
 */
OMPI_DECLSPEC extern ompi_predefined_op_t ompi_mpi_op_band;

/**
 * Global variable for MPI_LOR
 */
OMPI_DECLSPEC extern ompi_predefined_op_t ompi_mpi_op_lor;

/**
 * Global variable for MPI_BOR
 */
OMPI_DECLSPEC extern ompi_predefined_op_t ompi_mpi_op_bor;

/**
 * Global variable for MPI_LXOR
 */
OMPI_DECLSPEC extern ompi_predefined_op_t ompi_mpi_op_lxor;

/**
 * Global variable for MPI_BXOR
 */
OMPI_DECLSPEC extern ompi_predefined_op_t ompi_mpi_op_bxor;

/**
 * Global variable for MPI_MAXLOC
 */
OMPI_DECLSPEC extern ompi_predefined_op_t ompi_mpi_op_maxloc;

/**
 * Global variable for MPI_MINLOC
 */
OMPI_DECLSPEC extern ompi_predefined_op_t ompi_mpi_op_minloc;

/**
 * Global variable for MPI_REPLACE
 */
OMPI_DECLSPEC extern ompi_predefined_op_t ompi_mpi_op_replace;


/**
 * Table for Fortran <-> C op handle conversion
 */
extern struct opal_pointer_array_t *ompi_op_f_to_c_table;

/**
 * Initialize the op interface.
 *
 * @returns OMPI_SUCCESS Upon success
 * @returns OMPI_ERROR Otherwise
 *
 * Invoked from ompi_mpi_init(); sets up the op interface, creates
 * the predefined MPI operations, and creates the corresopnding F2C
 * translation table.
 */
int ompi_op_init(void);

/**
 * Finalize the op interface.
 *
 * @returns OMPI_SUCCESS Always
 *
 * Invokes from ompi_mpi_finalize(); tears down the op interface, and
 * destroys the F2C translation table.
 */
int ompi_op_finalize(void);

/**
 * Create a ompi_op_t
 *
 * @param commute Boolean indicating whether the operation is
 *        communative or not
 * @param func Function pointer of the error handler
 *
 * @returns op Pointer to the ompi_op_t that will be
 *   created and returned
 *
 * This function is called as the back-end of all the MPI_OP_CREATE
 * functions.  It creates a new ompi_op_t object, initializes it to
 * the correct object type, and sets the callback function on it.
 *
 * The type of the function pointer is (arbitrarily) the fortran
 * function handler type.  Since this function has to accept 2
 * different function pointer types (lest we have 2 different
 * functions to create errhandlers), the fortran one was picked
 * arbitrarily.  Note that (void*) is not sufficient because at
 * least theoretically, a sizeof(void*) may not necessarily be the
 * same as sizeof(void(*)).
 *
 * NOTE: It *always* sets the "fortran" flag to false.  The Fortran
 * wrapper for MPI_OP_CREATE is expected to reset this flag to true
 * manually.
 */
ompi_op_t *ompi_op_create(bool commute, ompi_op_fortran_handler_fn_t *func);

/**
 * Mark an MPI_Op as holding a C++ callback function, and cache
 * that function in the MPI_Op.  See a lenghty comment in
 * ompi/mpi/cxx/op.c::ompi_mpi_cxx_op_intercept() for a full
 * expalantion.
 */
OMPI_DECLSPEC void ompi_op_set_cxx_callback(ompi_op_t *op, MPI_User_function *fn);

/**
 * Check to see if an op is intrinsic.
 *
 * @param op The op to check
 *
 * @returns true If the op is intrinsic
 * @returns false If the op is not intrinsic
 *
 * Self-explanitory.  This is needed in a few top-level MPI functions;
 * this function is provided to hide the internal structure field
 * names.
 */
static inline bool ompi_op_is_intrinsic(ompi_op_t *op)
{
  return (bool) (0 != (op->o_flags & OMPI_OP_FLAGS_INTRINSIC));
}


/**
 * Check to see if an op is communative or not
 *
 * @param op The op to check
 *
 * @returns true If the op is communative
 * @returns false If the op is not communative
 *
 * Self-explanitory.  This is needed in a few top-level MPI functions;
 * this function is provided to hide the internal structure field
 * names.
 */
static inline bool ompi_op_is_commute(ompi_op_t *op)
{
  return (bool) (0 != (op->o_flags & OMPI_OP_FLAGS_COMMUTE));
}

/**
 * Check to see if an op is floating point associative or not
 *
 * @param op The op to check
 *
 * @returns true If the op is floating point associative
 * @returns false If the op is not floating point associative
 *
 * Self-explanitory.  This is needed in a few top-level MPI functions;
 * this function is provided to hide the internal structure field
 * names.
 */
static inline bool ompi_op_is_float_assoc(ompi_op_t *op)
{
  return (bool) (0 != (op->o_flags & OMPI_OP_FLAGS_FLOAT_ASSOC));
}


/**
 * Check to see if an op is valid on a given datatype
 *
 * @param op The op to check
 * @param ddt The datatype to check
 *
 * @returns true If the op is valid on that datatype
 * @returns false If the op is not valid on that datatype
 *
 * Self-explanitory.  This is needed in a few top-level MPI functions;
 * this function is provided to hide the internal structure field
 * names.
 */
static inline bool ompi_op_is_valid(ompi_op_t *op, ompi_datatype_t *ddt,
                                    char **msg, const char *func)
{
    /* Check:
       - non-intrinsic ddt's cannot be invoked on intrinsic op's
       - if intrinsic ddt invoked on intrinsic op:
           - ensure the datatype is defined in the op map
           - ensure we have a function pointer for that combination
    */

    if (ompi_op_is_intrinsic(op)) {
        if (ompi_ddt_is_predefined(ddt)) {
            /* Intrinsic ddt on intrinsic op */
            if ((-1 == ompi_op_ddt_map[ddt->id] ||
                 (0 != (op->o_flags & OMPI_OP_FLAGS_FORTRAN_FUNC) &&
                  NULL == op->o_func[ompi_op_ddt_map[ddt->id]].fort_fn) ||
                 (0 == (op->o_flags & OMPI_OP_FLAGS_FORTRAN_FUNC) &&
                  NULL == op->o_func[ompi_op_ddt_map[ddt->id]].c_fn))) {
                asprintf(msg, "%s: the reduction operation %s is not defined on the %s datatype",
                         func, op->o_name, ddt->name);
                return false;
            }
        } else {
            /* Non-intrinsic ddt on intrinsic op */
            if ('\0' != ddt->name[0]) {
                asprintf(msg, "%s: the reduction operation %s is not defined for non-intrinsic datatypes (attempted with datatype named \"%s\")",
                         func, op->o_name, ddt->name);
            } else {
                asprintf(msg, "%s: the reduction operation %s is not defined for non-intrinsic datatypes",
                         func, op->o_name);
            }
            return false;
        }
    }

    /* All other cases ok */
    return true;
}


/**
 * Perform a reduction operation.
 *
 * @param op The operation (IN)
 * @param source Source (input) buffer (IN)
 * @param target Target (output) buffer (IN/OUT)
 * @param count Number of elements (IN)
 * @param dtype MPI datatype (IN)
 *
 * @returns void As with MPI user-defined reduction functions, there
 * is no return code from this function.
 *
 * Perform a reduction operation with count elements of type dtype in
 * the buffers source and target.  The target buffer obtains the
 * result (i.e., the original values in the target buffer are reduced
 * with the values in the source buffer and the result is stored in
 * the target buffer).
 *
 * This function figures out which reduction operation function to
 * invoke and whether to invoke it with C- or Fortran-style invocation
 * methods.  If the op is intrinsic and has the operation defined for
 * dtype, the appropriate back-end function will be invoked.
 * Otherwise, the op is assumed to be a user op and the first function
 * pointer in the op array will be used.
 *
 * NOTE: This function assumes that a correct combination will be
 * given to it; it makes no provision for errors (in the name of
 * optimization).  If you give it an intrinsic op with a datatype that
 * is not defined to have that operation, it is likely to seg fault.
 */
static inline void ompi_op_reduce(ompi_op_t *op, void *source, void *target,
                                  int count, ompi_datatype_t *dtype)
{
  MPI_Fint f_dtype, f_count;

  /*
   * Call the reduction function.  Two dimensions: a) if both the op
   * and the datatype are intrinsic, we have a series of predefined
   * functions for each datatype, b) if the op has a fortran callback
   * function or not.
   *
   * NOTE: We assume here that we will get a valid result back from
   * the ompi_op_ddt_map[] (and not -1) -- if we do, then the
   * parameter check in the top-level MPI function should have caught
   * it.  If we get -1 because the top-level parameter check is turned
   * off, then it's an erroneous program and it's the user's fault.
   * :-)
   */

  if (0 != (op->o_flags & OMPI_OP_FLAGS_INTRINSIC) &&
     ompi_ddt_is_predefined(dtype)) {
    if (0 != (op->o_flags & OMPI_OP_FLAGS_FORTRAN_FUNC)) {
      f_dtype = OMPI_INT_2_FINT(dtype->d_f_to_c_index);
      f_count = OMPI_INT_2_FINT(count);
      op->o_func[ompi_op_ddt_map[dtype->id]].fort_fn(source, target,
                                                     &f_count, &f_dtype);
    } else {
      op->o_func[ompi_op_ddt_map[dtype->id]].c_fn(source, target, &count,
                                                  &dtype);
    }
  } 

  /* User-defined function */

  else if (0 != (op->o_flags & OMPI_OP_FLAGS_FORTRAN_FUNC)) {
    f_dtype = OMPI_INT_2_FINT(dtype->d_f_to_c_index);
    f_count = OMPI_INT_2_FINT(count);
    op->o_func[0].fort_fn(source, target, &f_count, &f_dtype);
  } else if (0 != (op->o_flags & OMPI_OP_FLAGS_CXX_FUNC)) {
    op->o_func[0].cxx_intercept_fn(source, target, &count, &dtype,
                                   op->o_func[1].c_fn);
  } else {
    op->o_func[0].c_fn(source, target, &count, &dtype);
  }
}

/**
 * Perform a reduction operation.
 *
 * @param op The operation (IN)
 * @param source Source1 (input) buffer (IN)
 * @param source Source2 (input) buffer (IN)
 * @param target Target (output) buffer (IN/OUT)
 * @param count Number of elements (IN)
 * @param dtype MPI datatype (IN)
 *
 * @returns void As with MPI user-defined reduction functions, there
 * is no return code from this function.
 *
 * Perform a reduction operation with count elements of type dtype in
 * the buffers source and target.  The target buffer obtains the
 * result (i.e., the original values in the target buffer are reduced
 * with the values in the source buffer and the result is stored in
 * the target buffer).
 *
 * This function figures out which reduction operation function to
 * invoke and whether to invoke it with C- or Fortran-style invocation
 * methods.  If the op is intrinsic and has the operation defined for
 * dtype, the appropriate back-end function will be invoked.
 * Otherwise, the op is assumed to be a user op and the first function
 * pointer in the op array will be used.
 *
 * NOTE: This function assumes that a correct combination will be
 * given to it; it makes no provision for errors (in the name of
 * optimization).  If you give it an intrinsic op with a datatype that
 * is not defined to have that operation, it is likely to seg fault.
 */
static inline void ompi_3buff_op_reduce(ompi_op_t *op, void *source1, void *source2, 
        void *target, int count, ompi_datatype_t *dtype)
{
  MPI_Fint f_dtype, f_count;
  void * restrict src1;
  void * restrict src2;
  void * restrict tgt;
  src1=source1;
  src2=source2;
  tgt=target;

  /*
   * Call the reduction function.  Two dimensions: a) if both the op
   * and the datatype are intrinsic, we have a series of predefined
   * functions for each datatype, b) if the op has a fortran callback
   * function or not.
   *
   * NOTE: We assume here that we will get a valid result back from
   * the ompi_op_ddt_map[] (and not -1) -- if we do, then the
   * parameter check in the top-level MPI function should have caught
   * it.  If we get -1 because the top-level parameter check is turned
   * off, then it's an erroneous program and it's the user's fault.
   * :-)
   */

  if (0 != (op->o_flags & OMPI_OP_FLAGS_INTRINSIC) &&
     ompi_ddt_is_predefined(dtype)) {
    if (0 != (op->o_flags & OMPI_OP_FLAGS_FORTRAN_FUNC)) {
      f_dtype = OMPI_INT_2_FINT(dtype->d_f_to_c_index);
      f_count = OMPI_INT_2_FINT(count);
      op->o_3buff_func[ompi_op_ddt_map[dtype->id]].fort_fn(src1, src2 , tgt,
                                                     &f_count, &f_dtype);
    } else {
      op->o_3buff_func[ompi_op_ddt_map[dtype->id]].c_fn(src1, src2, tgt,&count,
                                                  &dtype);
    }
  } 

  /* User-defined function - this can't work, will never be called.
   *  need to take this out soon. */

  else if (0 != (op->o_flags & OMPI_OP_FLAGS_FORTRAN_FUNC)) {
    f_dtype = OMPI_INT_2_FINT(dtype->d_f_to_c_index);
    f_count = OMPI_INT_2_FINT(count);
    op->o_3buff_func[0].fort_fn(src1, src2, tgt, &f_count, &f_dtype);
  } else if (0 != (op->o_flags & OMPI_OP_FLAGS_CXX_FUNC)) {
    op->o_3buff_func[0].cxx_intercept_fn(src1, src2, tgt, &count, &dtype,
                                   op->o_func[1].c_fn);
  } else {
    op->o_3buff_func[0].c_fn(src1, src2, tgt, &count, &dtype);
  }
}
#if defined(c_plusplus) || defined(__cplusplus)
}
#endif

#endif /* OMPI_OP_H */