Provided by: openmpi-doc_2.1.1-8_all bug

NAME

       shmem_comp4_xor_to_all(3),        shmem_int_xor_to_all(3),       shmem_int4_xor_to_all(3),
       shmem_int8_xor_to_all(3),     shmem_long_xor_to_all(3),      shmem_longlong_xor_to_all(3),
       shmem_short_xor_to_all(3)  - Performs a bitwise XOR operation on symmetric arrays over the
       active set of PEs.

SYNOPSIS

       C or C++:
       #include <mpp/shmem.h>

       void shmem_int_xor_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_xor_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_xor_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_xor_to_all(short *target, const short *source,
         int nreduce, int PE_start, int logPE_stride, int PE_size,
         short *pWrk, long *pSync);

       Fortran:
       INCLUDE "mpp/shmem.fh"

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

       CALL SHMEM_COMP4_XOR_TO_ALL(target, source, nreduce,
       & PE_start, logPE_stride, PE_size, pWrk, pSync)

       CALL SHMEM_INT4_XOR_TO_ALL(target, source, nreduce,
       & PE_start, logPE_stride, PE_size, pWrk, pSync)

       CALL SHMEM_INT8_XOR_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 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_comp8_xor_to_all: Complex, with an element size equal to two 8-
                     byte real values

              shmem_comp4_xor_to_all: Complex, with an element size equal to two 4-
                     byte real values

              shmem_int8_xor_to_all: Integer, with an element size of 8 bytes

              shmem_int4_xor_to_all: Integer, with an element size of 4 bytes

              shmem_real8_xor_to_all: Real, with an element size of 8 bytes

              shmem_real4_xor_to_all: Real, 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   is  of  type  long  and  size
              _SHMEM_REDUCE_SYNC_SIZE.  In  Fortran,  pSync  is  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 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 computes the
       exclusive OR of 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, FOOXOR, PWRK(MAX(NR/2+1,SHMEM_REDUCE_MIN_WRKDATA_SIZE))
       COMMON /COM/ FOO, FOOXOR, PWRK
       INTRINSIC MY_PE

       IF ( MOD(MY_PE(),2) .EQ. 0) THEN
         CALL SHMEM_REAL8_XOR_TO_ALL(FOOXOR, FOO, NR, 0, 1, N$PES/2,
         & PWRK, PSYNC)
         PRINT *, 'Result on PE ', MY_PE(), ' is ', FOOXOR
       ENDIF

       Example 2: Consider the following C/C++ call:
       shmem_short_xor_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_short_xor_to_all(&(target[0]), &(source[0]), 1, 0, 0, 8,
         pwrk1, psync1);
       shmem_short_xor_to_all(&(target[1]), &(source[1]), 1, 0, 0, 8,
         pwrk2, psync2);
       shmem_short_xor_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.

SEE ALSO

       intro_shmem(3)