.. _shmem_short_and_to_all:


shmem_short_and_to_all
======================

.. include_body

:ref:`shmem_int_and_to_all`\ (3), shmem_int4_and_to_all\ (3),
shmem_int8_and_to_all\ (3), :ref:`shmem_long_and_to_all`\ (3),
:ref:`shmem_longlong_and_to_all`\ (3), :ref:`shmem_short_and_to_all`\ (3) -
Performs a bitwise AND operation on symmetric arrays over the active set
of PEs.


SYNOPSIS
--------

C or C++:

.. code-block:: c++

   #include <mpp/shmem.h>

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

   void shmem_longlong_and_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_and_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_INT4_AND_TO_ALL(target, source, nreduce,
   & PE_start, logPE_stride, PE_size, pWrk, pSync)

   CALL SHMEM_INT8_AND_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).

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. 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 arguments are as follows:

target
   A symmetric array, of length nreduce elements, to receive the result
   of the reduction operations. The data type of target varies with the
   version of the reduction routine being called. 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_int8_and_to_all: Integer, with an element size of 8 bytes

   shmem_int4_and_to_all: Integer, with an element size of 4 bytes

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 must be of type long and size
   \_SHMEM_REDUCE_SYNC_SIZE. In Fortran, pSync must be of type integer
   and size SHMEM_REDUCE_SYNC_SIZE. If you are using Fortran, 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 to avoid 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 logical AND of the integer 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 PWRK(MAX(NR/2+1, SHMEM_REDUCE_MIN_WRKDATA_SIZE))
   INTEGER FOO, FOOAND
   COMMON /COM/ FOO, FOOAND, PWRK
   INTRINSIC MY_PE

   IF ( MOD(MY_PE(),2) .EQ. 0) THEN
     CALL SHMEM_INT8_AND_TO_ALL(FOOAND, FOO, NR, 0, 1, N$PES/2,
     & PWRK, PSYNC)
     PRINT *, 'Result on PE ', MY_PE(), ' is ', FOOAND
   ENDIF

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

.. code-block:: c

   shmem_int_and_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_and_to_all(&(target[0]), &(source[0]), 1, 0, 0, 8,
     pwrk1, psync1);

   shmem_int_and_to_all(&(target[1]), &(source[1]), 1, 0, 0, 8,
     pwrk2, psync2);

   shmem_int_and_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::
   *f90*\ (1) *intro_shmem*\ (3)
