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RTOp_parallel_helpers.c
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00001 /*
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00004 // 
00005 // RTOp: Interfaces and Support Software for Vector Reduction Transformation
00006 //       Operations
00007 //                Copyright (2006) Sandia Corporation
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00043 */
00044 
00045 #include "RTOp_parallel_helpers.h"
00046 
00047 #define MY_MIN(a,b) ( (a) < (b) ? (a) : (b) )
00048 #define MY_MAX(a,b) ( (a) > (b) ? (a) : (b) )
00049 
00050 void RTOp_parallel_calc_overlap(
00051   Teuchos_Index global_dim_in, Teuchos_Index local_sub_dim_in, Teuchos_Index local_off_in
00052   ,const Teuchos_Index first_ele_off_in, const Teuchos_Index sub_dim_in, const Teuchos_Index global_off_in
00053   ,Teuchos_Index* overlap_first_local_ele_off, Teuchos_Index* overalap_local_sub_dim
00054   ,Teuchos_Index* overlap_global_off
00055   )
00056 {
00057   Teuchos_Index  global_sub_dim = 0;
00058 #ifdef RTOp_DEBUG
00059   assert( overlap_first_local_ele_off );
00060   assert( overalap_local_sub_dim );
00061   assert( overlap_global_off );
00062   /* ToDo: Check the rest of the preconditions! */
00063 #endif
00064   /* Dimension of global sub-vector */
00065   global_sub_dim = sub_dim_in >= 0 ? sub_dim_in : global_dim_in - first_ele_off_in;
00066   /*
00067    * We need to determine if the local elements stored in this process overlap
00068    * with the global sub-vector that the client has requested.
00069    */
00070   if( !(
00071         local_off_in + local_sub_dim_in < first_ele_off_in + 1
00072         ||
00073         first_ele_off_in + global_sub_dim < local_off_in + 1
00074         )
00075     )
00076   {
00077     /* 
00078      * Determine how much of the local sub-vector stored in this process gets operated on. 
00079      * If (first_ele_off_in-1) <= local_off_in, then we start at the first element 
00080      * in this process.  Otherwise, we need to to increment by first_ele_off_in - local_off_in 
00081      */
00082     *overlap_first_local_ele_off = first_ele_off_in <= local_off_in ? 0 : first_ele_off_in - local_off_in;
00083     /*
00084      * Deterime the number of elements in the local sub-vector that overlap with the
00085      * requested logical sub-vector.
00086      */
00087     *overalap_local_sub_dim  = (
00088       MY_MIN(first_ele_off_in+global_sub_dim,local_off_in+local_sub_dim_in) /* last overlap element plus 1 in process */
00089       -
00090       MY_MAX(first_ele_off_in,local_off_in)                                 /* first overlap element in process */
00091       );
00092     /*
00093      * Finally, figure out where this local sub-vectors fit into the logical
00094      * vector that the client has specified with global_off_in and
00095      * first_ele_off_in.  Note that the element this->(first_ele_off) acts as
00096      * the the first element in the logical vector defined by the client if
00097      * gloabal_offset_in == 0.  Therefore, we need to subtract
00098      * first_ele_off_in from local_off_in to get the true offset into the
00099      * logicl vector defined by the client.  Then we can adjust it by adding
00100      * global_off_in to place it into the clients actual logical vector..
00101      */
00102     *overlap_global_off   = (
00103       ( first_ele_off_in > local_off_in
00104         ? 0
00105         : local_off_in - first_ele_off_in
00106         )                 /* First element in 'v' in logical sub-vector 'g' */
00107       + global_off_in     /* Adding adjustment into logical sub-vector 'p' */
00108       );
00109   }
00110   else {
00111     *overlap_first_local_ele_off = -1; /* No overlap */
00112   }
00113 }
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