[Freeciv-Dev] Re: (PR#3444) index_to_map_pos macro

["Jason Short" <jdorje@xxxxxxxxxxxxxxxxxxxxx>]

Gregory Berkolaiko wrote:
> The macro inverts the action of map_inx: extracts the map coordinates from 
> the index.  Also added are macros CHECK_INDEX (similar to CHECK_MAP_POS) 
> and MAX_INDEX for sanity checking and allocations.
> 
> I intend to adapt the PF code to use this and map_inx code shortly, so 
> please commit.

> Index: common/map.h
> ===================================================================
> RCS file: /home/freeciv/CVS/freeciv/common/map.h,v
> retrieving revision 1.135
> diff -u -r1.135 map.h
> --- common/map.h      2003/02/10 21:43:41     1.135
> +++ common/map.h      2003/02/16 16:35:04
> @@ -222,6 +222,21 @@
>  #define map_inx(x,y) \
>    (CHECK_MAP_POS((x),(y)), (x)+(y)*map.xsize)
>  
> +/* Maximum value of index (for sanity checks and allocations) */
> +#define MAX_INDEX map.xsize * map.ysize
> +
> +#ifdef DEBUG
> +#define CHECK_INDEX(index) assert((index) >= 0 && (index) < MAX_INDEX)
> +#else
> +#define CHECK_INDEX(index) ((void)0)
> +#endif
> +
> +/* index_to_map_pos(int, int *, int *) inverts map_inx */
> +#define index_to_map_pos(index, x, y) \
> +(    CHECK_INDEX(index),              \
> +     *(x) = (index) % map.xsize,      \
> +     *(y) = (index) / map.ysize)
> +
>  #define DIRSTEP(dest_x, dest_y, dir) \
>  (    (dest_x) = DIR_DX[(dir)],       \
>       (dest_y) = DIR_DY[(dir)])

The preferred form for these conversion functions is (dest, source) - 
like memcpy, strcpy, etc.  I also prefer to call the values map_x, map_y 
- to indicate that they are map positions (which will become relevant 
shortly).

In the patch below, I also renamed MAX_INDEX as MAX_MAP_INDEX and moved 
CHECK_INDEX up next to CHECK_MAP_POS.

Note, Ross has a form of this that will work on non-normal (e.g., 
negative) index positions.  We could use that form instead, although it 
is slower.  If we don't do that, we could probably optimize it as:

   map_y = index / map.xsize
   map_x = index - map_y * map.xsize;

which is likely to be faster than using %.  But I'd rather see the 
interface be implemented first - we can work on the implementation later.

jason

Index: common/map.h
===================================================================
RCS file: /home/freeciv/CVS/freeciv/common/map.h,v
retrieving revision 1.135
diff -u -r1.135 map.h
--- common/map.h        2003/02/10 21:43:41     1.135
+++ common/map.h        2003/02/16 22:37:54
@@ -203,10 +203,15 @@
 void initialize_move_costs(void);
 void reset_move_costs(int x, int y);
 
+/* Maximum value of index (for sanity checks and allocations) */
+#define MAX_MAP_INDEX map.xsize * map.ysize
+
 #ifdef DEBUG
 #define CHECK_MAP_POS(x,y) assert(is_normal_map_pos((x),(y)))
+#define CHECK_INDEX(index) assert((index) >= 0 && (index) < MAX_MAP_INDEX)
 #else
 #define CHECK_MAP_POS(x,y) ((void)0)
+#define CHECK_INDEX(index) ((void)0)
 #endif
 
 #define map_adjust_x(X)            \
@@ -221,6 +226,12 @@
 
 #define map_inx(x,y) \
   (CHECK_MAP_POS((x),(y)), (x)+(y)*map.xsize)
+
+/* index_to_map_pos(int *, int *, int) inverts map_inx */
+#define index_to_map_pos(pmap_x, pmap_y, index) \
+  (CHECK_INDEX(index),                          \
+   *(pmap_x) = (index) % map.xsize,             \
+   *(pmap_y) = (index) / map.ysize)
 
 #define DIRSTEP(dest_x, dest_y, dir)   \
 (    (dest_x) = DIR_DX[(dir)],         \