[Freeciv-Dev] Re: the directional system

[Raimar Falke <hawk@xxxxxxxxxxxxxxxxxxxxxxx>]

On Fri, Sep 07, 2001 at 02:18:45PM +0200, Raimar Falke wrote:
> On Fri, Sep 07, 2001 at 04:51:36AM -0700, Trent Piepho wrote:
> > On Fri, 7 Sep 2001, Jason Dorje Short wrote:
> > 
> > +#define DIR_REVERSE(dir) (((dir) + 4) % 8)
> > 
> > This is a faster way to do it.  Modulus operations are very expensive, but a
> > bitwise and is very cheap.
> > 
> > +#define DIR_REVERSE(dir) (((dir) + 4) & 7)

As one last experiment I change the current (7-dir) to the general
form which will always work in every direction system:

diff -urd -X freeciv.current/diff_ignore freeciv.current/common/map.h 
work/common/map.h
--- freeciv.current/common/map.h        Fri Sep 14 09:31:33 2001
+++ work/common/map.h   Fri Sep 14 18:47:39 2001
@@ -442,7 +442,16 @@
 };

 /* return the reverse of the direction */
-#define DIR_REVERSE(dir) (7 - (dir))
+#define DIR_REVERSE(dir) \
+((dir)==DIR8_WEST?DIR8_EAST: \
+ ((dir)==DIR8_EAST?DIR8_WEST: \
+  ((dir)==DIR8_NORTH?DIR8_SOUTH: \
+   ((dir)==DIR8_SOUTH?DIR8_NORTH: \
+    ((dir)==DIR8_NORTHWEST?DIR8_SOUTHEAST: \
+     ((dir)==DIR8_NORTHEAST?DIR8_SOUTHWEST: \
+      ((dir)==DIR8_SOUTHWEST?DIR8_NORTHEAST: \
+       ((dir)==DIR8_SOUTHEAST?DIR8_NORTHWEST: \
+       (dir)/0))))))))

 /* is the direction "cardinal"?  Cardinal directions
  * (also called cartesian) are the four main ones */

So what do you expect as a slowdown? 10%? 5%? 2%? 1%? 0.1%? Not
measurable?

7-dir:
user    1m32.890s
user    1m32.730s
user    1m33.030s
user    1m32.890s
user    1m32.460s
user    1m32.720s
user    1m32.750s
average: 92.781s

general way:
user    1m33.800s
user    1m33.730s
user    1m33.540s
user    1m33.790s
user    1m33.810s
user    1m33.860s
user    1m33.610s
average: 93.734s

So the general form is 1% slower.

        Raimar

-- 
 email: rf13@xxxxxxxxxxxxxxxxx
 "At the beginning of the week, we sealed ten BSD programmers
  into a computer room with a single distribution of BSD Unix.
  Upon opening the room after seven days, we found all ten programmers 
  dead, clutching each other's throats, and thirteen new flavors of BSD."