.. _shmem_short_sum_to_all:


shmem_short_sum_to_all
======================

.. include_body

shmem_comp4_sum_to_all\ (3), shmem_comp8_sum_to_all\ (3),
:ref:`shmem_complexd_sum_to_all`\ (3), :ref:`shmem_complexf_sum_to_all`\ (3),
:ref:`shmem_double_sum_to_all`\ (3), :ref:`shmem_float_sum_to_all`\ (3),
:ref:`shmem_int_sum_to_all`\ (3), shmem_int4_sum_to_all\ (3),
shmem_int8_sum_to_all\ (3), :ref:`shmem_long_sum_to_all`\ (3),
:ref:`shmem_longdouble_sum_to_all`\ (3), :ref:`shmem_longlong_sum_to_all`\ (3),
shmem_real4_sum_to_all\ (3), shmem_real8_sum_to_all\ (3),
shmem_real16_sum_to_all\ (3), :ref:`shmem_short_sum_to_all`\ (3) - Performs
a sum reduction across a set of processing elements (PEs)


SYNOPSIS
--------

C or C++:

.. code-block:: c++

   #include <mpp/shmem.h>

   void shmem_complexd_sum_to_all(double complex *target,
     const double complex *source, int nreduce, int PE_start,
     int logPE_stride, int PE_size, double complex *pWrk,
     long *pSync)

   void shmem_complexf_sum_to_all(float complex *target,
     const float complex *source, int nreduce, int PE_start,
     int logPE_stride, int PE_size, float complex *pWrk,
     long *pSync)

   void shmem_double_sum_to_all(double *target,
     const double *source, int nreduce, int PE_start, int logPE_stride,
     int PE_size, double *pWrk, long *pSync)

   void shmem_float_sum_to_all(float *target, const float *source,
     int nreduce, int PE_start, int logPE_stride, int PE_size,
     float *pWrk, long *pSync)

   void shmem_int_sum_to_all(int *target, const int *source,
     int nreduce, int PE_start, int logPE_stride, int PE_size,
     int *pWrk, long *pSync)

   void shmem_long_sum_to_all(long *target, const long *source,
     int nreduce, int PE_start, int logPE_stride, int PE_size,
     long *pWrk, long *pSync)

   void shmem_longdouble_sum_to_all(long double *target,
     const long double *source, int nreduce, int PE_start, int
     logPE_stride, int PE_size, long double *pWrk, long *pSync)

   void shmem_longlong_sum_to_all(long long *target,
     const long long *source, int nreduce, int PE_start,
     int logPE_stride, int PE_size, long long *pWrk,
     long *pSync)

   void shmem_short_sum_to_all(short *target, const short *source,
     int nreduce, int PE_start, int logPE_stride, int PE_size,
     short *pWrk, long *pSync)

Fortran:

.. code-block:: fortran

   INCLUDE "mpp/shmem.fh"

   INTEGER pSync(SHMEM_REDUCE_SYNC_SIZE)
   INTEGER nreduce, PE_start, logPE_stride, PE_size

   CALL SHMEM_COMP4_SUM_TO_ALL(target, source, nreduce,
   & PE_start, logPE_stride, PE_size, pWrk, pSync)

   CALL SHMEM_COMP8_SUM_TO_ALL(target, source, nreduce,
   & PE_start, logPE_stride, PE_size, pWrk, pSync)

   CALL SHMEM_INT4_SUM_TO_ALL(target, source, nreduce,
   & PE_start, logPE_stride, PE_size, pWrk, pSync)

   CALL SHMEM_INT8_SUM_TO_ALL(target, source, nreduce,
   & PE_start, logPE_stride, PE_size, pWrk, pSync)

   CALL SHMEM_REAL4_SUM_TO_ALL(target, source, nreduce,
   & PE_start, logPE_stride, PE_size, pWrk, pSync)

   CALL SHMEM_REAL8_SUM_TO_ALL(target, source, nreduce,
   & PE_start, logPE_stride, PE_size, pWrk, pSync)

   CALL SHMEM_REAL16_SUM_TO_ALL(target, source, nreduce,
   & PE_start, logPE_stride, PE_size, pWrk, pSync)


DESCRIPTION
-----------

The shared memory (SHMEM) reduction routines compute one or more
reductions across symmetric arrays on multiple virtual PEs. A reduction
performs an associative binary operation across a set of values. For a
list of other SHMEM reduction routines, see *intro_shmem*\ (3).

As with all SHMEM collective routines, each of these routines assumes
that only PEs in the active set call the routine. If a PE not in the
active set calls a SHMEM collective routine, undefined behavior results.

The nreduce argument determines the number of separate reductions to
perform. The source array on all PEs in the active set provides one
element for each reduction. The results of the reductions are placed in
the target array on all PEs in the active set. The active set is defined
by the PE_start, logPE_stride, PE_size triplet.

The source and target arrays may be the same array, but they may not be
overlapping arrays.

The arguments are as follows:

target
   The remotely accessible integer data object to be updated on the
   remote PE. If you are using C/C++, the type of target should match
   that implied in the SYNOPSIS section. If you are using the Fortran
   compiler, it must be of type integer with an element size of 4 bytes
   for SHMEM_INT4_ADD and 8 bytes for SHMEM_INT8_ADD.

value
   The value to be atomically added to target. If you are using C/C++,
   the type of value should match that implied in the SYNOPSIS section.
   If you are using Fortran, it must be of type integer with an element
   size of target.

pe
   An integer that indicates the PE number upon which target is to be
   updated. If you are using Fortran, it must be a default integer
   value.

target
   | A symmetric array of length nreduce elements to receive the results
     of the reduction operations.
   | The data type of target varies with the version of the reduction
     routine being called and the language used. When calling from
     C/C++, refer to the SYNOPSIS section for data type information.
     When calling from Fortran, the target data types are as follows:

   shmem_comp4_sum_to_all:** COMPLEX(KIND=4).

   shmem_comp8_sum_to_all:** Complex. If you are using Fortran, it must be
      a default complex value.

   shmem_int4_sum_to_all:** INTEGER(KIND=4).

   shmem_int8_sum_to_all:** Integer. If you are using Fortran, it must be a
      default integer value.

   shmem_real4_sum_to_all:** REAL(KIND=4).

   shmem_real8_sum_to_all:** Real. If you are using Fortran, it must be a
      default real value.

   shmem_real16_sum_to_all:** Real. If you are using Fortran, it must be a
      default real value.

source
   A symmetric array, of length nreduce elements, that contains one
   element for each separate reduction operation. The source argument
   must have the same data type as target.

nreduce
   The number of elements in the target and source arrays. nreduce must
   be of type integer. If you are using Fortran, it must be a default
   integer value.

PE_start
   The lowest virtual PE number of the active set of PEs. PE_start must
   be of type integer. If you are using Fortran, it must be a default
   integer value.

logPE_stride
   The log (base 2) of the stride between consecutive virtual PE numbers
   in the active set. logPE_stride must be of type integer. If you are
   using Fortran, it must be a default integer value.

PE_size
   The number of PEs in the active set. PE_size must be of type integer.
   If you are using Fortran, it must be a default integer value.

pWrk
   A symmetric work array. The pWrk argument must have the same data
   type as target. In C/C++, this contains max(nreduce/2 + 1,
   \_SHMEM_REDUCE_MIN_WRKDATA_SIZE) elements. In Fortran, this contains
   max(nreduce/2 + 1, SHMEM_REDUCE_MIN_WRKDATA_SIZE) elements.

pSync
   A symmetric work array. In C/C++, pSync is of type long and size
   \_SHMEM_REDUCE_SYNC_SIZE. In Fortran, pSync is of type integer and
   size SHMEM_REDUCE_SYNC_SIZE. It must be a default integer value.
   Every element of this array must be initialized with the value
   \_SHMEM_SYNC_VALUE (in C/C++) or SHMEM_SYNC_VALUE (in Fortran) before
   any of the PEs in the active set enter the reduction routine.

The values of arguments nreduce, PE_start, logPE_stride, and PE_size
must be equal on all PEs in the active set. The same target and source
arrays, and the same pWrk and pSync work arrays, must be passed to all
PEs in the active set.

Before any PE calls a reduction routine, you must ensure that the
following conditions exist (synchronization via a barrier or some other
method is often needed to ensure this): The pWrk and pSync arrays on all
PEs in the active set are not still in use from a prior call to a
collective SHMEM routine. The target array on all PEs in the active set
is ready to accept the results of the reduction.

Upon return from a reduction routine, the following are true for the
local PE: The target array is updated. The values in the pSync array are
restored to the original values.


NOTES
-----

The terms collective, symmetric, and cache aligned are defined in
*intro_shmem*\ (3).

All SHMEM reduction routines reset the values in pSync before they
return, so a particular pSync buffer need only be initialized the first
time it is used.

You must ensure that the pSync array is not being updated on any PE in
the active set while any of the PEs participate in processing of a SHMEM
reduction routine. Be careful of the following situations: If the pSync
array is initialized at run time, some type of synchronization is needed
to ensure that all PEs in the working set have initialized pSync before
any of them enter a SHMEM routine called with the pSync synchronization
array. A pSync or pWrk array can be reused in a subsequent reduction
routine call only if none of the PEs in the active set are still
processing a prior reduction routine call that used the same pSync or
pWrk arrays. In general, this can be assured only by doing some type of
synchronization. However, in the special case of reduction routines
being called with the same active set, you can allocate two pSync and
pWrk arrays and alternate between them on successive calls.


EXAMPLES
--------

**Example 1:** This Fortran example statically initializes the pSync
array and finds the sum of the real variable FOO across all even PEs.

::

   INCLUDE "mpp/shmem.fh"

   INTEGER PSYNC(SHMEM_REDUCE_SYNC_SIZE)
   DATA PSYNC /SHMEM_REDUCE_SYNC_SIZE*SHMEM_SYNC_VALUE/
   PARAMETER (NR=1)
   REAL FOO, FOOSUM, PWRK(MAX(NR/2+1,SHMEM_REDUCE_MIN_WRKDATA_SIZE))
   COMMON /COM/ FOO, FOOSUM, PWRK
   INTRINSIC MY_PE

   IF ( MOD(MY_PE(),2) .EQ. 0) THEN
     CALL SHMEM_INT4_SUM_TO_ALL(FOOSUM, FOO, NR, 0, 1, N$PES/2,
     & PWRK, PSYNC)
     PRINT *, 'Result on PE ', MY_PE(), ' is ', FOOSUM
   ENDIF

**Example 2:** Consider the following C/C++ call:

.. code-block:: c++

   shmem_int_sum_to_all( target, source, 3, 0, 0, 8, pwrk, psync );

The preceding call is more efficient, but semantically equivalent to,
the combination of the following calls:

::

   shmem_int_sum_to_all(&(target[0]), &(source[0]), 1, 0, 0, 8,
     pwrk1, psync1);
   shmem_int_sum_to_all(&(target[1]), &(source[1]), 1, 0, 0, 8,
     pwrk2, psync2);
   shmem_int_sum_to_all(&(target[2]), &(source[2]), 1, 0, 0, 8,
     pwrk1, psync1);

   Note that two sets of pWrk and pSync arrays are used alternately because no
   synchronization is done between calls.


.. seealso::
   *intro_shmem*\ (3)
