[freeciv-ai] (PR#12243) bug: compute_tech_sell_price is overly symmetric

["Mateusz Stefek" <mstefek@xxxxxxxxx>]

<URL: http://bugs.freeciv.org/Ticket/Display.html?id=12243 >

> [bhudson - Sun Feb 13 22:57:34 2005]:
> 
> Mateusz made a nice patch in #12129, and I responded he shouldn't
> change the logic.
> 
> Turns out he should have:
>       /* Don't risk it falling into enemy hands */
>       if (pplayers_allied(taker, eplayer) &&
>           is_player_dangerous(giver, eplayer)) {
>         return BIG_NUMBER;
>       }
> 
> Means that in the attached (hacked) savegame, the Germans evaluate the
> worth
> of Alphabet as 33,333.  So I can get quite a lot from them -- Radio,
> for instance.
> 
> The reason?  They're allied with the chileans, and I'm at war with
> them.
> Therefore, I evaluate alphabet as being dangerous to give away.  And
> the
> germans are willing to pay for that!
> 
> I'm not sure how to design the logic to avoid this.
> 
> 
> Another comment is that the cost to me shouldn't be 100k for something
> as minor as Alphabet.  It should be based on the value my enemy places
> on the tech, which would be about 100.
> 
Ok. Here's a patch
--
mateusz 

Index: ai/advdiplomacy.c
===================================================================
RCS file: /home/freeciv/CVS/freeciv/ai/advdiplomacy.c,v
retrieving revision 1.65
diff -u -r1.65 advdiplomacy.c
--- ai/advdiplomacy.c   12 Feb 2005 09:54:02 -0000      1.65
+++ ai/advdiplomacy.c   15 Feb 2005 11:57:58 -0000
@@ -199,14 +199,18 @@
   Calculate a price of a tech.
   Note that both AI players always evaluate the tech worth symetrically
   This eases tech exchange.
+  is_dangerous returns ig the giver is afraid of giving that tech
+  (the taker should evaluate it normally, but giver should never give that)
 **********************************************************************/
 static int compute_tech_sell_price(struct player* giver, struct player* taker,
-                               int tech_id)
+                               int tech_id, bool* is_dangerous)
 {
     int worth;
     
     worth = ai_goldequiv_tech(taker, tech_id);
     
+    *is_dangerous = FALSE;
+    
     /* Share and expect being shared brotherly between allies */
     if (pplayers_allied(giver, taker)) {
       worth /= 2;
@@ -232,7 +236,7 @@
       /* Don't risk it falling into enemy hands */
       if (pplayers_allied(taker, eplayer) &&
           is_player_dangerous(giver, eplayer)) {
-        return BIG_NUMBER;
+        *is_dangerous = TRUE;
       }
       
       if (pplayers_allied(taker, eplayer) &&
@@ -262,6 +266,7 @@
   bool give = (pplayer == pclause->from);
   int giver;
   struct ai_dip_intel *adip = &ai->diplomacy.player_intel[aplayer->player_no];
+  bool is_dangerous;
 
   assert(pplayer != aplayer);
   
@@ -273,9 +278,14 @@
   case CLAUSE_ADVANCE:
     
     if (give) {
-      worth -= compute_tech_sell_price(pplayer, aplayer, pclause->value);
+      worth -= compute_tech_sell_price(pplayer, aplayer, pclause->value,
+                                       &is_dangerous);
+      if (is_dangerous) {
+        return -BIG_NUMBER;
+      }
     } else if (get_invention(pplayer, pclause->value) != TECH_KNOWN) {
-      worth += compute_tech_sell_price(aplayer, pplayer, pclause->value);
+      worth += compute_tech_sell_price(aplayer, pplayer, pclause->value,
+                                       &is_dangerous);
     }
 
   break;
@@ -955,6 +965,7 @@
                                   struct player* player2)
 {
   int worth[game.num_tech_types];
+  bool is_dangerous;
     
   tech_type_iterate(tech) {
     if (tech == A_NONE) {
@@ -963,13 +974,23 @@
     }
     if (get_invention(player1, tech) == TECH_KNOWN) {
       if (get_invention(player2, tech) != TECH_KNOWN) {
-        worth[tech] = -compute_tech_sell_price(player1, player2, tech);
+        worth[tech] = -compute_tech_sell_price(player1, player2, tech,
+                                              &is_dangerous);
+       if (is_dangerous) {
+         /* don't try to exchange */
+         worth[tech] = 0;
+       }
       } else {
         worth[tech] = 0;
       }
     } else {
       if (get_invention(player2, tech) == TECH_KNOWN) {
-        worth[tech] = compute_tech_sell_price(player2, player1, tech);
+        worth[tech] = compute_tech_sell_price(player2, player1, tech,
+                                             &is_dangerous);
+       if (is_dangerous) {
+         /* don't try to exchange */
+         worth[tech] = 0;
+       }
       } else {
         worth[tech] = 0;
       }