From 955f70279a978b2bbd0a0f89eb601e79becdee44 Mon Sep 17 00:00:00 2001
From: schnetter <schnetter@1bf05452-ddb3-4880-bfa1-00436340132b>
Date: Thu, 22 May 2003 17:05:42 +0000
Subject: Make TAT/Periodic work when the domain is smaller than the ghost
 zone.

git-svn-id: http://svn.cactuscode.org/arrangements/CactusNumerical/Periodic/trunk@6 1bf05452-ddb3-4880-bfa1-00436340132b
---
 src/periodic.c | 86 +++++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 67 insertions(+), 19 deletions(-)

diff --git a/src/periodic.c b/src/periodic.c
index d63e065..0f65ff0 100644
--- a/src/periodic.c
+++ b/src/periodic.c
@@ -73,6 +73,18 @@ BndPeriodicVI (cGH const * restrict const cctkGH,
   for (dir=0; dir<group.dim; ++dir) {
     if (dir<3 && do_periodic[dir]) {
       
+      assert (stencil[dir] >= 0);
+      
+      if (data.gsh[dir] < 2*stencil[dir]+1) {
+        CCTK_VWarn (0, __LINE__, __FILE__, CCTK_THORNSTRING,
+                    "The group %s has in direction %d only %d grid points.  "
+                    "This is not large enough for a periodic boundary that is %d grid points wide.  "
+                    "The group needs to have at least %d grid points in direction %d.",
+                    CCTK_GroupNameFromVarI(vi), dir, data.gsh[dir],
+                    stencil[dir],
+                    2*stencil[dir]+1, dir);
+      }
+      
       /* Loop over faces */
       for (f=0; f<2; ++f) {
         
@@ -102,28 +114,64 @@ BndPeriodicVI (cGH const * restrict const cctkGH,
           xferinfo[d].flip  = 0;
         }
         
-        if (cctkGH->cctk_bbox[2*dir+f]) {
-          if (f==0) {
-            /* Fill in lower face */
-            xferinfo[dir].src.off = data.gsh[dir] - 2 * stencil[dir];
-            xferinfo[dir].src.len = stencil[dir];
-            xferinfo[dir].dst.len = stencil[dir];
-          } else {
-            /* Fill in upper face */
-            xferinfo[dir].src.off = stencil[dir];
-            xferinfo[dir].src.len = stencil[dir];
-            xferinfo[dir].dst.off = data.gsh[dir] - stencil[dir];
-            xferinfo[dir].dst.len = stencil[dir];
+        {
+          int const domain_size = data.gsh[dir] - 2*stencil[dir];
+          int step_size = stencil[dir];
+          int num_steps = 1;
+          int step;
+          int source;
+          
+          assert (domain_size > 0);
+          if (f==0 && domain_size < step_size) {
+            /* TODO: this could be made more efficient by taking
+               larger steps */
+            step_size = 1;
+            num_steps = stencil[dir];
           }
-        } else {
-          xferinfo[dir].src.len = 0;
-          xferinfo[dir].dst.len = 0;
+          
+          for (step=0; step<num_steps; ++step) {
+            
+            if (cctkGH->cctk_bbox[2*dir+f]) {
+              if (f==0) {
+                /* Fill in lower face */
+#if 0
+                xferinfo[dir].src.off = data.gsh[dir] - 2 * stencil[dir];
+                xferinfo[dir].src.len = stencil[dir];
+                xferinfo[dir].dst.len = stencil[dir];
+#endif
+                source = data.gsh[dir] - 2 * stencil[dir] + step;
+                while (source < stencil[dir]) {
+                  source += domain_size;
+                }
+                while (source >= data.gsh[dir]-stencil[dir]) {
+                  source -= domain_size;
+                }
+                assert (source >= stencil[dir]);
+                assert (source < data.gsh[dir]-stencil[dir]);
+                xferinfo[dir].src.off = source;
+                xferinfo[dir].src.len = step_size;
+                xferinfo[dir].dst.off = step;
+                xferinfo[dir].dst.len = step_size;
+              } else {
+                /* Fill in upper face */
+                xferinfo[dir].src.off = stencil[dir];
+                xferinfo[dir].src.len = stencil[dir];
+                xferinfo[dir].dst.off = data.gsh[dir] - stencil[dir];
+                xferinfo[dir].dst.len = stencil[dir];
+              }
+            } else {
+              xferinfo[dir].src.len = 0;
+              xferinfo[dir].dst.len = 0;
+            }
+            
+            ierr = Slab_Transfer
+              (cctkGH, group.dim, xferinfo, -1,
+               group.vartype, varptr, group.vartype, varptr);
+            assert (!ierr);
+            
+          } /* for step */
         }
         
-        ierr = Slab_Transfer (cctkGH, group.dim, xferinfo, -1,
-                              group.vartype, varptr, group.vartype, varptr);
-        assert (!ierr);
-        
       } /* for f */
       
     } /* if dir */
-- 
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