Correclty move the pointer at the top-level when moving from proxy to proxy....

Correclty move the pointer at the top-level when moving from proxy to proxy. Simplify the linking recursion.

src/cell.c

@@ -101,7 +101,33 @@ int cell_getsize(struct cell *c) {
  *
  * @return The number of particles linked.
  */
-int cell_link_parts(struct cell *c, struct part *parts, int link) {
+int cell_link_parts(struct cell *c, struct part *parts) {
+
+  c->hydro.parts = parts;
+
+  /* Fill the progeny recursively, depth-first. */
+  if (c->split) {
+    int offset = 0;
+    for (int k = 0; k < 8; k++) {
+      if (c->progeny[k] != NULL)
+        offset += cell_link_parts(c->progeny[k], &parts[offset]);
+    }
+  }
+
+  /* Return the total number of linked particles. */
+  return c->hydro.count;
+}
+
+
+/**
+ * @brief Link the cells recursively to the given #part array.
+ *
+ * @param c The #cell.
+ * @param parts The #part array.
+ *
+ * @return The number of particles linked.
+ */
+int cell_link_foreign_parts(struct cell *c, struct part *parts) {
 
 #ifdef SWIFT_DEBUG_CHECKS
   if (c->nodeID == engine_rank)
@@ -110,37 +136,28 @@ int cell_link_parts(struct cell *c, struct part *parts, int link) {
 
   /* Do we have a hydro task at this level? */
   if (c->hydro.density != NULL) {
-    link = 1;
-  }
 
-  /* Ok, link the particles at this level */
-  if (link) {
-    c->hydro.parts = parts;
+    /* Recursively attach the parts */
+    const int counts = cell_link_parts(c, parts);
+#ifdef SWIFT_DEBUG_CHECKS
+    if (counts != c->hydro.count)
+      error("Something is wrong with the foreign counts");
+#endif
+    return counts;
   }
 
-  /* Fill the progeny recursively, depth-first. */
+  /* Go deeper to find the level where the tasks are */
   if (c->split) {
     int count = 0;
-
     for (int k = 0; k < 8; k++) {
       if (c->progeny[k] != NULL) {
-        count += cell_link_parts(c->progeny[k], &parts[count], link);
+        count += cell_link_foreign_parts(c->progeny[k], parts);
       }
     }
-
-#ifdef SWIFT_DEBUG_CHECKS
-    if (link && (count != c->hydro.count))
-      error("Something is wrong with the foreign part counts.");
-#endif
-
     return count;
-  }
-
-  /* Return the total number of linked particles. */
-  if (link)
-    return c->hydro.count;
-  else
+  } else {
     return 0;
+  }
 }
 
 /**

src/cell.h

@@ -688,7 +688,8 @@ int cell_unpack_end_step(struct cell *c, struct pcell_step *pcell);
 int cell_pack_multipoles(struct cell *c, struct gravity_tensors *m);
 int cell_unpack_multipoles(struct cell *c, struct gravity_tensors *m);
 int cell_getsize(struct cell *c);
-int cell_link_parts(struct cell *c, struct part *parts, int link);
+int cell_link_parts(struct cell *c, struct part *parts);
+int cell_link_foreign_parts(struct cell *c, struct part *parts);
 int cell_link_gparts(struct cell *c, struct gpart *gparts);
 int cell_link_sparts(struct cell *c, struct spart *sparts);
 int cell_count_parts_for_tasks(const struct cell *c);

src/engine.c

@@ -1793,20 +1793,24 @@ void engine_allocate_foreign_particles(struct engine *e) {
   }
 
   struct part *parts = s->parts_foreign;
-  size_t count_parts = 0;
+  size_t total_count_parts = 0;
   for (int k = 0; k < nr_proxies; k++) {
     for (int j = 0; j < e->proxies[k].nr_cells_in; j++) {
 
       if (e->proxies[k].cells_in_type[j] & proxy_cell_type_hydro) {
 
-        count_parts +=
-            cell_link_parts(e->proxies[k].cells_in[j], parts, /*link=*/0);
-        parts += count_parts;
+        const size_t count_parts = cell_link_foreign_parts(e->proxies[k].cells_in[j], parts);
+        parts = &parts[count_parts];
+	total_count_parts += count_parts;
       }
     }
   }
 
-  message("count_parts: %zd %zd", count_parts_in, count_parts);
+  /* Update the counters */
+  s->nr_parts_foreign = parts - s->parts_foreign;
+
+  
+  message("count_parts: %zd %zd", count_parts_in, total_count_parts);
 
   return;