Index: client/goto.c
===================================================================
RCS file: /home/freeciv/CVS/freeciv/client/goto.c,v
retrieving revision 1.26
diff -u -r1.26 goto.c
--- client/goto.c	2001/09/23 16:09:34	1.26
+++ client/goto.c	2001/10/07 11:48:26
@@ -390,7 +390,7 @@
 		   || is_non_allied_city_tile(pdesttile, unit_owner(punit))) {
 	  add_to_queue = 0;
 	  move_cost = SINGLE_MOVE;
-	} else if (psrctile->move_cost[dir] != -3) {/*is -3 if sea units can move between*/
+	} else if (psrctile->move_cost[dir] != MOVE_COST_FOR_VALID_SEA_STEP) {
 	  continue;
 	} else if (unit_flag(punit, F_TRIREME) 
 		   && trireme_loss_pct(unit_owner(punit), x1, y1) > 0) {
Index: common/map.c
===================================================================
RCS file: /home/freeciv/CVS/freeciv/common/map.c,v
retrieving revision 1.93
diff -u -r1.93 map.c
--- common/map.c	2001/10/01 11:08:13	1.93
+++ common/map.c	2001/10/07 11:48:28
@@ -999,27 +999,46 @@
 }
 
 /***************************************************************
-  Similar to tile_move_cost_ptrs, but for pre-calculating
-  tile->move_cost[] values for use by ai (?)
-  If either terrain is T_UNKNOWN, then return 'maxcost'.
-  If both are ocean, or one is ocean and other city,
-  return -3, else if either is ocean return maxcost.
-  Otherwise, return normal cost (unit-independent).
+  tile_move_cost_ai is used to fill the move_cost array of struct
+  tile. The cached values of this array are used in server/gotohand.c
+  and client/goto.c. tile_move_cost_ai returns the move cost as
+  calculated by tile_move_cost_ptrs (with no unit pointer to get
+  unit-independent results) EXCEPT if either of the source or
+  destination tile is an ocean tile. Then the result of the method
+  shows if a ship can take the step from the source position to the
+  destination position (return value is MOVE_COST_FOR_VALID_SEA_STEP)
+  or not (return value is maxcost).
+
+  A ship can take the step if:
+    - both tiles are ocean or
+    - one of the tiles is ocean and the other is a city or is unknown
 ***************************************************************/
 static int tile_move_cost_ai(struct tile *tile0, struct tile *tile1,
 			     int x, int y, int x1, int y1, int maxcost)
 {
   assert(is_real_tile(x, y));
-  assert(!is_server || (tile0->terrain != T_UNKNOWN && tile1->terrain != T_UNKNOWN));
+  assert(!is_server
+	 || (tile0->terrain != T_UNKNOWN && tile1->terrain != T_UNKNOWN));
+
+  if (tile0->terrain == T_OCEAN && tile1->terrain == T_OCEAN) {
+    return MOVE_COST_FOR_VALID_SEA_STEP;
+  }
+
+  if (tile0->terrain == T_OCEAN
+      && (tile1->city || tile1->terrain == T_UNKNOWN)) {
+    return MOVE_COST_FOR_VALID_SEA_STEP;
+  }
+
+  if (tile1->terrain == T_OCEAN
+      && (tile0->city || tile0->terrain == T_UNKNOWN)) {
+    return MOVE_COST_FOR_VALID_SEA_STEP;
+  }
 
-  if (tile0->terrain == T_OCEAN) {
-    return (tile1->city || tile1->terrain == T_OCEAN
-	    || tile1->terrain == T_UNKNOWN) ? -3 : maxcost;
-  } else if (tile1->terrain == T_OCEAN) {
-    return (tile0->city || tile0->terrain == T_UNKNOWN) ? -3 : maxcost;
-  } else {
-    return tile_move_cost_ptrs(NULL, tile0, tile1, x, y, x1, y1);
+  if (tile0->terrain == T_OCEAN || tile1->terrain == T_OCEAN) {
+    return maxcost;
   }
+
+  return tile_move_cost_ptrs(NULL, tile0, tile1, x, y, x1, y1);
 }
 
 /***************************************************************
Index: common/map.h
===================================================================
RCS file: /home/freeciv/CVS/freeciv/common/map.h,v
retrieving revision 1.94
diff -u -r1.94 map.h
--- common/map.h	2001/09/27 22:49:53	1.94
+++ common/map.h	2001/10/07 11:48:28
@@ -20,7 +20,8 @@
 
 struct Sprite;			/* opaque; client-gui specific */
 
-#define NUM_DIRECTION_NSEW 16
+#define NUM_DIRECTION_NSEW 		16
+#define MOVE_COST_FOR_VALID_SEA_STEP	(-3)
 
 struct map_position {
   int x,y;
Index: server/gotohand.c
===================================================================
RCS file: /home/freeciv/CVS/freeciv/server/gotohand.c,v
retrieving revision 1.121
diff -u -r1.121 gotohand.c
--- server/gotohand.c	2001/10/06 12:01:29	1.121
+++ server/gotohand.c	2001/10/07 11:48:30
@@ -342,11 +342,13 @@
         move_cost = SINGLE_MOVE;
         move_cost += warmap.seacost[x][y];
         if (warmap.seacost[x1][y1] > move_cost && move_cost < maxcost) {
-	  /* by adding the move_cost to the warmap regardless if we can move between
-	     we allow for shore bombardment/transport to inland positions/etc. */
+	  /* by adding the move_cost to the warmap regardless if we
+	     can move between we allow for shore bombardment/transport
+	     to inland positions/etc. */
           warmap.seacost[x1][y1] = move_cost;
-          if (ptile->move_cost[dir] == -3) /* -3 means ships can move between */
+	  if (ptile->move_cost[dir] == MOVE_COST_FOR_VALID_SEA_STEP) {
 	    add_to_mapqueue(move_cost, x1, y1);
+	  }
 	}
 	break;
       default:
@@ -702,9 +704,11 @@
 	if (warmap.seacost[x1][y1] <= warmap.seacost[x][y])
 	  continue; /* No need for all the calculations */
 
-	if (psrctile->move_cost[dir] != -3 /* is -3 if sea units can move between */
-	    && (dest_x != x1 || dest_y != y1)) /* allow ships to target a shore */
+	/* allow ships to target a shore */
+	if (psrctile->move_cost[dir] != MOVE_COST_FOR_VALID_SEA_STEP
+	    && (dest_x != x1 || dest_y != y1)) {
 	  continue;
+	}
 	else if (unit_flag(punit, F_TRIREME)
 		 && trireme_loss_pct(unit_owner(punit), x1, y1) > 0) {
 	  move_cost = 2*SINGLE_MOVE+1;