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Subject: [freeciv-ai] Re: [Freeciv-Dev] (PR#12682) AI Ignores Building Effects for Tech. Wants
From: "Benedict Adamson" <badamson@xxxxxxxxxxx>
Date: Mon, 26 Dec 2005 15:21:37 -0800
Reply-to: bugs@xxxxxxxxxxx

<URL: http://bugs.freeciv.org/Ticket/Display.html?id=12682 >

I wrote:
 > After examining the AI city improvement code, I can not find anywhere
 > that the AI increases its want (pplayer->ai.tech_want[t]) for a
 > technology because that technology allows improvements that have a
 > particular desirable effect.
...

Attached is a patch that fixes this. Testing with the Ancients rule-set
shows, for example, that the AI will now research Construction, which
for that rule-set enables several useful buildings but not any units
(not even indirectly).

The patch increases the tech_want for technologies that enable useful
improvements (for example, Ceremonial Burial enabling Temple) and for
technologies that enhance improvements (for example, Mysticism enhances
Temple). It decreases the tech_want for technologies that will render
useful improvements obsolete.

Once this patch is applied, the code can easilly be enhanced to
encourage building of improvements that will enable subsequent
improvements (for example, Library enables University).

This version of the patch incorporates amendments because of feedback 
from Vasco.

diff -ruN -Xvendor.freeciv.current/diff_ignore 
vendor.freeciv.current/ai/aicity.c freeciv.PR12682/ai/aicity.c
--- vendor.freeciv.current/ai/aicity.c  2005-12-19 22:41:47.000000000 +0000
+++ freeciv.PR12682/ai/aicity.c 2005-12-26 12:22:42.000000000 +0000
@@ -25,6 +25,7 @@
 #include "fcintl.h"
 #include "game.h"
 #include "government.h"
+#include "improvement.h"
 #include "log.h"
 #include "map.h"
 #include "movement.h"
@@ -240,33 +241,507 @@
 }
 
 /************************************************************************** 
-  Calculate effects. A few base variables:
+  Increase want for a technology because of the value of that technology
+  in providing an improvement effect.
+
+  The input building_want gives the desire for the improvement;
+  the value may be negative for technologies that produce undesirable
+  effects.
+
+  This function must convert from units of 'building want' to 'tech want'.
+  We put this conversion in a function because the 'want' scales are
+  unclear and kludged. Consequently, this conversion might require tweaking.
+**************************************************************************/
+static void want_tech_for_improvement_effect(struct player *pplayer,
+                                            const struct city *pcity,
+                                            const Impr_type_id id,
+                                            Tech_type_id tech,
+                                            int building_want)
+{
+  /* WAG */
+  const int tech_want = building_want * pcity->ai.recalc_interval * 14 / 8;
+#if 0
+  /* This logging is relatively expensive,
+   * so activate it only while necessary. */
+  TECH_LOG(LOG_DEBUG, pplayer, tech,
+    "wanted by %s for %s: %d -> %d",
+    pcity->name, get_improvement_name(id),
+    building_want, tech_want);
+#endif
+  pplayer->ai.tech_want[tech] += tech_want;
+}
+
+/************************************************************************** 
+  How desirable is a particular effect for a particular city?
+  Expressed as an adjustment of the base value (v)
+  given the number of cities in range (c).
+**************************************************************************/
+static int improvement_effect_value(struct player *pplayer,
+                                   struct government *gov,
+                                   const struct ai_data *ai,
+                                   const struct city *pcity,
+                                   const bool capital, 
+                                   const struct impr_type *pimpr,
+                                   const struct effect *peffect,
+                                   const int c,
+                                   const int nplayers,
+                                   int v)
+{
+  int amount = peffect->value;
+
+  switch (peffect->type) {
+  /* These (Wonder) effects have already been evaluated in base_want() */
+  case EFT_CAPITAL_CITY:
+  case EFT_UPKEEP_FREE:
+  case EFT_POLLU_POP_PCT:
+  case EFT_POLLU_PROD_PCT:
+  case EFT_OUTPUT_BONUS:
+  case EFT_OUTPUT_BONUS_2:
+  case EFT_OUTPUT_ADD_TILE:
+  case EFT_OUTPUT_INC_TILE:
+  case EFT_OUTPUT_PER_TILE:
+  case EFT_OUTPUT_WASTE:
+  case EFT_OUTPUT_WASTE_BY_DISTANCE:
+  case EFT_OUTPUT_WASTE_PCT:
+  case EFT_SPECIALIST_OUTPUT:
+    break;
+
+  case EFT_CITY_VISION_RADIUS_SQ:
+  case EFT_UNIT_VISION_RADIUS_SQ:
+    /* Wild guess.  "Amount" is the number of tiles (on average) that
+     * will be revealed by the effect.  Note that with an omniscient
+     * AI this effect is actually not useful at all. */
+    v += c * amount;
+    break;
+
+  case EFT_SLOW_DOWN_TIMELINE:
+    /* AI doesn't care about these. */
+    break;
+
+    /* WAG evaluated effects */
+  case EFT_INCITE_COST_PCT:
+    v += c * amount / 100;
+    break;
+  case EFT_MAKE_HAPPY:
+    v += (get_entertainers(pcity) + pcity->ppl_unhappy[4]) * 5 * amount;
+    if (city_list_size(pplayer->cities)
+       > game.info.cityfactor 
+       + get_player_bonus(pplayer, EFT_EMPIRE_SIZE_MOD)) {
+      v += c * amount; /* offset large empire size */
+    }
+    v += c * amount;
+    break;
+  case EFT_UNIT_RECOVER:
+    /* TODO */
+    break;
+  case EFT_NO_UNHAPPY:
+    v += (get_entertainers(pcity) + pcity->ppl_unhappy[4]) * 30;
+    break;
+  case EFT_FORCE_CONTENT:
+  case EFT_MAKE_CONTENT:
+    if (get_city_bonus(pcity, EFT_NO_UNHAPPY) <= 0) {
+      int factor = 2;
+
+      v += MIN(amount, pcity->ppl_unhappy[4] + get_entertainers(pcity)) * 35;
+
+      /* Try to build wonders to offset empire size unhappiness */
+      if (city_list_size(pplayer->cities) 
+         > game.info.cityfactor 
+         + get_player_bonus(pplayer, EFT_EMPIRE_SIZE_MOD)) {
+       if (get_player_bonus(pplayer, EFT_EMPIRE_SIZE_MOD) > 0) {
+         factor += city_list_size(pplayer->cities) 
+           / get_player_bonus(pplayer, EFT_EMPIRE_SIZE_STEP);
+       }
+       factor += 2;
+      }
+      v += factor * c * amount;
+    }
+    break;
+  case EFT_MAKE_CONTENT_MIL_PER:
+    if (get_city_bonus(pcity, EFT_NO_UNHAPPY) <= 0) {
+      v += MIN(pcity->ppl_unhappy[4] + get_entertainers(pcity),
+              amount) * 25;
+      v += MIN(amount, 5) * c;
+    }
+    break;
+  case EFT_MAKE_CONTENT_MIL:
+    if (get_city_bonus(pcity, EFT_NO_UNHAPPY) <= 0) {
+      v += pcity->ppl_unhappy[4] * amount
+        * MAX(unit_list_size(pcity->units_supported), 0) * 2;
+      v += c * MAX(amount + 2, 1);
+    }
+    break;
+  case EFT_TECH_PARASITE:
+    {
+      int turns;
+      int bulbs;
+      int value;
+         
+      if (nplayers <= amount) {
+       break;
+      }
+          
+      turns = 9999;
+      bulbs = 0;
+      players_iterate(aplayer) {
+       int potential = aplayer->bulbs_last_turn
+         + city_list_size(aplayer->cities) + 1;
+       if (tech_exists(pimpr->obsolete_by)) {
+         turns = MIN(turns, 
+                     total_bulbs_required_for_goal(aplayer, pimpr->obsolete_by)
+                     / (potential + 1));
+       }
+       if (players_on_same_team(aplayer, pplayer)) {
+         continue;
+       }
+       bulbs += potential;
+      } players_iterate_end;
+  
+      /* For some number of turns we will be receiving bulbs for free
+       * Bulbs should be amortized properly for each turn.
+       * We use formula for the sum of geometric series:
+       */
+      value = bulbs * (1.0 - pow(1.0 - (1.0 / MORT), turns)) * MORT;
+         
+      value = value  * (100 - game.info.freecost)        
+       * (nplayers - amount) / (nplayers * amount * 100);
+         
+      /* WAG */
+      value /= 3;
+
+      CITY_LOG(LOG_DEBUG, pcity,
+              "%s parasite effect: bulbs %d, turns %d, value %d", 
+              pimpr->name, bulbs, turns, value);
+       
+      v += value;
+      break;
+    }
+  case EFT_GROWTH_FOOD:
+    v += c * 4 + (amount / 7) * pcity->surplus[O_FOOD];
+    break;
+  case EFT_AIRLIFT:
+    /* FIXME: We need some smart algorithm here. The below is 
+     * totally braindead. */
+    v += c + MIN(ai->stats.units.land, 13);
+    break;
+  case EFT_ANY_GOVERNMENT:
+    if (!can_change_to_government(pplayer, ai->goal.govt.gov)) {
+      v += MIN(MIN(ai->goal.govt.val, 65),
+              num_unknown_techs_for_goal(pplayer, ai->goal.govt.req) * 10);
+    }
+    break;
+  case EFT_ENABLE_NUKE:
+    /* Treat nuke as a Cruise Missile upgrade */
+    v += 20 + ai->stats.units.missiles * 5;
+    break;
+  case EFT_ENABLE_SPACE:
+    if (game.info.spacerace) {
+      v += 5;
+      if (ai->diplomacy.production_leader == pplayer) {
+       v += 100;
+      }
+    }
+    break;
+  case EFT_GIVE_IMM_TECH:
+    if (!ai_wants_no_science(pplayer)) {
+      v += amount * (game.info.sciencebox + 1);
+    }
+    break;
+  case EFT_HAVE_EMBASSIES:
+    v += 5 * nplayers;
+    break;
+  case EFT_REVEAL_CITIES:
+  case EFT_NO_ANARCHY:
+    break;  /* Useless for AI */
+  case EFT_NO_SINK_DEEP:
+    v += 15 + ai->stats.units.triremes * 5;
+    break;
+  case EFT_NUKE_PROOF:
+    if (ai->threats.nuclear) {
+      v += pcity->size * unit_list_size(pcity->tile->units) * (capital + 1)
+       * amount / 100;
+    }
+    break;
+  case EFT_REVEAL_MAP:
+    if (!ai->explore.land_done || !ai->explore.sea_done) {
+      v += 10;
+    }
+    break;
+  case EFT_SIZE_UNLIMIT:
+    /* Note we look up the SIZE_UNLIMIT again right below.  This could
+     * be avoided... */
+    if (get_city_bonus(pcity, EFT_SIZE_UNLIMIT) == 0) {
+      amount = 20; /* really big city */
+    }
+    /* there not being a break here is deliberate, mind you */
+  case EFT_SIZE_ADJ:
+    if (get_city_bonus(pcity, EFT_SIZE_UNLIMIT) == 0) {
+      const int aqueduct_size = get_city_bonus(pcity, EFT_SIZE_ADJ);
+
+      if (!city_can_grow_to(pcity, pcity->size + 1)) {
+       v += pcity->surplus[O_FOOD] * ai->food_priority * amount;
+       if (pcity->size == aqueduct_size) {
+         v += 30 * pcity->surplus[O_FOOD];
+       }
+      }
+      v += c * amount * 4 / aqueduct_size;
+    }
+    break;
+  case EFT_SS_STRUCTURAL:
+  case EFT_SS_COMPONENT:
+  case EFT_SS_MODULE:
+    if (game.info.spacerace
+       /* If someone has started building spaceship already or
+        * we have chance to win a spacerace */
+       && (ai->diplomacy.spacerace_leader
+           || ai->diplomacy.production_leader == pplayer)) {
+      v += 95;
+    }
+    break;
+  case EFT_SPY_RESISTANT:
+    /* Uhm, problem: City Wall has -50% here!! */
+    break;
+  case EFT_MOVE_BONUS:
+    /* FIXME: check other reqs (e.g., unitclass) */
+    v += (8 * v * amount + ai->stats.units.land
+         + ai->stats.units.sea + ai->stats.units.air);
+    break;
+  case EFT_UNIT_NO_LOSE_POP:
+    v += unit_list_size(pcity->tile->units) * 2;
+    break;
+  case EFT_HP_REGEN:
+    /* FIXME: check other reqs (e.g., unitclass) */
+    v += (5 * c + ai->stats.units.land
+         + ai->stats.units.sea + ai->stats.units.air);
+    break;
+  case EFT_VETERAN_COMBAT:
+    /* FIXME: check other reqs (e.g., unitclass) */
+    v += (2 * c + ai->stats.units.land + ai->stats.units.sea
+         + ai->stats.units.air);
+    break;
+  case EFT_VETERAN_BUILD:
+    /* FIXME: check other reqs (e.g., unitclass, unitflag) */
+    v += (3 * c + ai->stats.units.land + ai->stats.units.sea
+         + ai->stats.units.air);
+    break;
+  case EFT_UPGRADE_UNIT:
+    v += ai->stats.units.upgradeable;
+    if (amount == 1) {
+      v *= 2;
+    } else if (amount == 2) {
+      v *= 3;
+    } else {
+      v *= 4;
+    }
+    break;
+  case EFT_DEFEND_BONUS:
+    if (ai_handicap(pplayer, H_DEFENSIVE)) {
+      v += amount / 10; /* make AI slow */
+    }
+    if (is_ocean(tile_get_terrain(pcity->tile))) {
+      v += ai->threats.ocean[-tile_get_continent(pcity->tile)]
+       ? amount/5 : amount/20;
+    } else {
+      adjc_iterate(pcity->tile, tile2) {
+       if (is_ocean(tile_get_terrain(tile2))) {
+         if (ai->threats.ocean[-tile_get_continent(tile2)]) {
+           v += amount/5;
+           break;
+         }
+       }
+      } adjc_iterate_end;
+    }
+    v += (amount/20 + ai->threats.invasions - 1) * c; /* for wonder */
+    if (ai->threats.continent[pcity->tile->continent]
+       || capital
+       || (ai->threats.invasions
+           && is_water_adjacent_to_tile(pcity->tile))) {
+      if (ai->threats.continent[pcity->tile->continent]) {
+       v += amount;
+      } else {
+       v += amount / (!ai->threats.igwall ? (15 - capital * 5) : 15);
+      }
+    }
+    break;
+  case EFT_NO_INCITE:
+    if (get_city_bonus(pcity, EFT_NO_INCITE) <= 0) {
+      v += MAX((game.info.diplchance * 2 
+               - game.info.incite_total_factor) / 2
+              - game.info.incite_improvement_factor * 5
+              - game.info.incite_unit_factor * 5, 0);
+    }
+    break;
+  case EFT_GAIN_AI_LOVE:
+    players_iterate(aplayer) {
+      if (aplayer->ai.control) {
+       if (ai_handicap(pplayer, H_DEFENSIVE)) {
+         v += amount / 10;
+       } else {
+         v += amount / 20;
+       }
+      }
+    } players_iterate_end;
+    break;
+  /* Currently not supported for building AI - wait for modpack users */
+  case EFT_UNHAPPY_FACTOR:
+  case EFT_UPKEEP_FACTOR:
+  case EFT_UNIT_UPKEEP_FREE_PER_CITY:
+  case EFT_CIVIL_WAR_CHANCE:
+  case EFT_EMPIRE_SIZE_MOD:
+  case EFT_EMPIRE_SIZE_STEP:
+  case EFT_MAX_RATES:
+  case EFT_MARTIAL_LAW_EACH:
+  case EFT_MARTIAL_LAW_MAX:
+  case EFT_RAPTURE_GROW:
+  case EFT_UNBRIBABLE_UNITS:
+  case EFT_REVOLUTION_WHEN_UNHAPPY:
+  case EFT_HAS_SENATE:
+  case EFT_INSPIRE_PARTISANS:
+  case EFT_HAPPINESS_TO_GOLD:
+  case EFT_FANATICS:
+  case EFT_NO_DIPLOMACY:
+  case EFT_OUTPUT_PENALTY_TILE:
+  case EFT_OUTPUT_INC_TILE_CELEBRATE:
+  case EFT_TRADE_REVENUE_BONUS:
+    break;
+  case EFT_LAST:
+    freelog(LOG_ERROR, "Bad effect type.");
+    break;
+  }
+
+  return v;
+}
+
+/************************************************************************** 
+  Increase the degree to which we want to meet a set of requirements,
+  because they will enable construction of an improvement
+  with desirable effects.
+
+  v is the desire for the improvement.
+
+  Returns whether all the requirements are met.
+**************************************************************************/
+static bool adjust_wants_for_reqs(struct player *pplayer,
+                                  struct city *pcity, 
+                                  struct impr_type *pimpr,
+                                  const int v)
+{
+  bool all_met = TRUE;
+  int n_needed_techs = 0;
+  int n_needed_improvements = 0;
+  /* For now, we hard-code the maximum number of needed technologies
+   * and improvements at 8 so we can use an efficient array
+   * rather than a slow genlist.
+   * For most rulesets, we expect at most 1 requirement of each.
+   */
+  Tech_type_id needed_techs[8];
+  Impr_type_id needed_improvements[8];
+
+  requirement_vector_iterate(&pimpr->reqs, preq) {
+    const bool active = is_req_active(pplayer, pcity, pimpr,
+                                      NULL, NULL, NULL, NULL, preq);
+    if (preq->source.type == REQ_TECH && n_needed_techs < 8 && !active) {
+      /* Found a missing technology requirement for this improvement. */
+      needed_techs[n_needed_techs++] = preq->source.value.tech;
+    } else if (preq->source.type == REQ_BUILDING && n_needed_improvements < 8
+               && !active) {
+      /* Found a missing improvement requirement for this improvement.
+       * For example, in the default ruleset a city must have a Library
+       * before it can have a University. */
+      needed_improvements[n_needed_improvements++] =
+        preq->source.value.building;
+    }
+    all_met = all_met && active;
+  } requirement_vector_iterate_end;
+
+  /* If v is negative, the improvement is not worth building,
+   * but there is no need to punish research of the technologies
+   * that would make it available.
+   */
+  if (0 < v && 0 < n_needed_techs) {
+    /* Because we want this improvements,
+     * we want the techs that will make it possible */
+    const int dv = v / n_needed_techs;
+    int t;
+
+    for (t = 0; t < n_needed_techs; t++) {
+      want_tech_for_improvement_effect(pplayer, pcity, pimpr->index,
+                                       needed_techs[t], dv);
+    }
+  }
+
+  /* If v is negative, the improvement is not worth building,
+   * but there is no need to punish building the improvements
+   * that would make it available.
+   */
+  if (0 < v && 0 < n_needed_improvements) {
+    /* Because we want this improvement,
+     * we want the improvements that will make it possible */
+    const int dv = v / (n_needed_improvements * 4); /* WAG */
+    int i;
+
+    for (i = 0; i < n_needed_improvements; i++) {
+      struct impr_type *needed_impr = get_improvement_type(
+                                        needed_improvements[i]);
+      /* TODO: increase the want for the needed_impr,
+       * if we can build it now */
+      /* Recurse */
+      (void)adjust_wants_for_reqs(pplayer, pcity, needed_impr, dv);
+    }
+  }
+
+  /* TODO: use a similar method to increase wants for governments
+   * that will make this improvement possible */
+
+  return all_met;
+}
+
+/************************************************************************** 
+  Calculate effects of possible improvements and extra effects of existing
+  improvements. Consequently adjust the desirability of those improvements
+  or the technologies that would make them possible.
+
+  This function may (indeed, should) be called even for improvements that a 
city
+  already has, or can not (yet) build. For existing improvements,
+  it will discourage research of technologies that would make the improvement
+  obsolete or reduce its effectiveness, and encourages technologies that would
+  improve its effectiveness. For improvements that the city can not yet build
+  it will encourage research of the techs and building of the improvements
+  that will make the improvement possible.
+
+  A complexity is that there are two sets of requirements to consider:
+  the requirements for the building itself, and the requirements for
+  the effects for the building.
+
+  A few base variables:
     c - number of cities we have in current range
     u - units we have of currently affected type
     v - the want for the improvement we are considering
 
   This function contains a whole lot of WAGs. We ignore cond_* for now,
-  thinking that one day we may fulfill the cond_s anyway. In general, we
+  thinking that one day we may fulfil the cond_s anyway. In general, we
   first add bonus for city improvements, then for wonders.
 
   IDEA: Calculate per-continent aggregates of various data, and use this
   for wonders below for better wonder placements.
 **************************************************************************/
-static void adjust_building_want_by_effects(struct city *pcity, 
-                                            Impr_type_id id)
+static void adjust_wants_by_effects1(struct player *pplayer,
+                                     struct city *pcity, 
+                                     struct impr_type *pimpr,
+                                     const bool already)
 {
-  struct player *pplayer = city_owner(pcity);
-  struct impr_type *pimpr = get_improvement_type(id);
   int v = 0;
   int cities[REQ_RANGE_LAST];
   int nplayers = game.info.nplayers - game.info.nbarbarians;
   struct ai_data *ai = ai_data_get(pplayer);
-  struct tile *ptile = pcity->tile;
   bool capital = is_capital(pcity);
+  bool can_build = TRUE;
+  struct government *gov = get_gov_pplayer(pplayer);
   struct req_source source = {
     .type = REQ_BUILDING,
-    .value = {.building = id}
+    .value = {.building = pimpr->index}
   };
+  const bool is_coinage = impr_flag(pimpr->index, IF_GOLD);
 
   /* Remove team members from the equation */
   players_iterate(aplayer) {
@@ -277,409 +752,155 @@
     }
   } players_iterate_end;
 
-  if (impr_flag(id, IF_GOLD)) {
+  if (is_coinage) {
     /* Since coinage contains some entirely spurious ruleset values,
-     * we need to return here with some spurious want. */
-    pcity->ai.building_want[id] = TRADE_WEIGHTING;
-    return;
+     * we need to hard-code a sensible want.
+     * We must otherwise handle the special IF_GOLD improvement
+     * like the others, so the AI will research techs that make it available,
+     * for rulesets that do not provide it from the start.
+     */
+    v += TRADE_WEIGHTING;
+  } else {
+    /* Base want is calculated above using a more direct approach. */
+    v += base_want(pplayer, pcity, pimpr->index);
+    if (v != 0) {
+      CITY_LOG(LOG_DEBUG, pcity, "%s base_want is %d (range=%d)", 
+               pimpr->name, v, ai->impr_range[pimpr->index]);
+    }
   }
 
-  /* Base want is calculated above using a more direct approach. */
-  v += base_want(pplayer, pcity, id);
-  if (v != 0) {
-    CITY_LOG(LOG_DEBUG, pcity, "%s base_want is %d (range=%d)", 
-             get_improvement_name(id), v, ai->impr_range[id]);
+  if (!is_coinage) {
+    /* Adjust by building cost */
+    /* FIXME: ought to reduce by upkeep cost and amortise by building cost */
+    v -= (impr_build_shield_cost(pimpr->index)
+         / (pcity->surplus[O_SHIELD] * 10 + 1));
   }
 
   /* Find number of cities per range.  */
   cities[REQ_RANGE_PLAYER] = city_list_size(pplayer->cities);
   cities[REQ_RANGE_WORLD] = cities[REQ_RANGE_PLAYER]; /* kludge. */
 
-  cities[REQ_RANGE_CONTINENT] = ai->stats.cities[ptile->continent];
+  cities[REQ_RANGE_CONTINENT] = ai->stats.cities[pcity->tile->continent];
 
   cities[REQ_RANGE_CITY] = 1;
   cities[REQ_RANGE_LOCAL] = 0;
 
   effect_list_iterate(get_req_source_effects(&source), peffect) {
-    struct requirement *mypreq;
-    bool useful;
+    struct requirement *mypreq = NULL;
+    bool active = TRUE;
+    /* For now, we hard-code the maximum number of needed technologies
+     * at 8 so we can use an efficient array rather than a slow genlist.
+     * For most rulesets, we expect at most 1 tech requirement.
+     */
+    Tech_type_id needed_techs[8];
+    int n_needed_techs = 0;
 
     if (is_effect_disabled(pplayer, pcity, pimpr,
                           NULL, NULL, NULL, NULL,
                           peffect)) {
-      CITY_LOG(LOG_DEBUG, pcity, "%s has a disabled effect: %s", 
-               get_improvement_name(id), effect_type_name(peffect->type));
       continue;
     }
 
-    mypreq = NULL;
-    useful = TRUE;
     requirement_list_iterate(peffect->reqs, preq) {
       /* Check if all the requirements for the currently evaluated effect
        * are met, except for having the building that we are evaluating. */
       if (preq->source.type == REQ_BUILDING
-         && preq->source.value.building == id) {
+         && preq->source.value.building == pimpr->index) {
        mypreq = preq;
         continue;
       }
       if (!is_req_active(pplayer, pcity, pimpr, NULL, NULL, NULL, NULL,
                         preq)) {
-       useful = FALSE;
-       break;
+       active = FALSE;
+       if (preq->source.type == REQ_TECH && n_needed_techs < 8) {
+         /* This missing requirement is a missing tech requirement.
+          * This will be for some additional effect
+          * (For example, in the default ruleset, Mysticism increases
+          * the effect of Temples). */
+         needed_techs[n_needed_techs++] = preq->source.value.tech;
+       }
       }
     } requirement_list_iterate_end;
 
-    if (useful) {
-      int amount = peffect->value, c = cities[mypreq->range];
-
-      switch (peffect->type) {
-      /* These have already been evaluated in base_want() */
-      case EFT_CAPITAL_CITY:
-      case EFT_UPKEEP_FREE:
-      case EFT_POLLU_POP_PCT:
-      case EFT_POLLU_PROD_PCT:
-      case EFT_OUTPUT_BONUS:
-      case EFT_OUTPUT_BONUS_2:
-      case EFT_OUTPUT_ADD_TILE:
-      case EFT_OUTPUT_INC_TILE:
-      case EFT_OUTPUT_PER_TILE:
-      case EFT_OUTPUT_WASTE:
-      case EFT_OUTPUT_WASTE_BY_DISTANCE:
-      case EFT_OUTPUT_WASTE_PCT:
-      case EFT_SPECIALIST_OUTPUT:
-         break;
-
-      case EFT_CITY_VISION_RADIUS_SQ:
-      case EFT_UNIT_VISION_RADIUS_SQ:
-       /* Wild guess.  "Amount" is the number of tiles (on average) that
-        * will be revealed by the effect.  Note that with an omniscient
-        * AI this effect is actually not useful at all. */
-       v += c * amount;
-       break;
-
-      case EFT_SLOW_DOWN_TIMELINE:
-       /* AI doesn't care about these. */
-       break;
-
-       /* WAG evaluated effects */
-       case EFT_INCITE_COST_PCT:
-         v += c * amount / 100;
-         break;
-       case EFT_MAKE_HAPPY:
-         v += (get_entertainers(pcity) + pcity->ppl_unhappy[4]) * 5 * amount;
-          if (city_list_size(pplayer->cities)
-                > game.info.cityfactor 
-                  + get_player_bonus(pplayer, EFT_EMPIRE_SIZE_MOD)) {
-            v += c * amount; /* offset large empire size */
-          }
-          v += c * amount;
-         break;
-       case EFT_UNIT_RECOVER:
-         /* TODO */
-         break;
-       case EFT_NO_UNHAPPY:
-         v += (get_entertainers(pcity) + pcity->ppl_unhappy[4]) * 30;
-         break;
-       case EFT_FORCE_CONTENT:
-       case EFT_MAKE_CONTENT:
-         if (get_city_bonus(pcity, EFT_NO_UNHAPPY) <= 0) {
-            int factor = 2;
-
-           v += MIN(amount, pcity->ppl_unhappy[4] + get_entertainers(pcity)) * 
35;
-
-            /* Try to build wonders to offset empire size unhappiness */
-            if (city_list_size(pplayer->cities) 
-                > game.info.cityfactor 
-                  + get_player_bonus(pplayer, EFT_EMPIRE_SIZE_MOD)) {
-              if (get_player_bonus(pplayer, EFT_EMPIRE_SIZE_MOD) > 0) {
-                factor += city_list_size(pplayer->cities) 
-                          / get_player_bonus(pplayer, EFT_EMPIRE_SIZE_STEP);
-              }
-              factor += 2;
-            }
-           v += factor * c * amount;
-         }
-         break;
-       case EFT_MAKE_CONTENT_MIL_PER:
-          if (get_city_bonus(pcity, EFT_NO_UNHAPPY) <= 0) {
-           v += MIN(pcity->ppl_unhappy[4] + get_entertainers(pcity),
-                    amount) * 25;
-           v += MIN(amount, 5) * c;
-         }
-         break;
-       case EFT_MAKE_CONTENT_MIL:
-          if (get_city_bonus(pcity, EFT_NO_UNHAPPY) <= 0) {
-           v += pcity->ppl_unhappy[4] * amount
-             * MAX(unit_list_size(pcity->units_supported), 0) * 2;
-           v += c * MAX(amount + 2, 1);
-         }
-         break;
-       case EFT_TECH_PARASITE:
-       {
-         int turns;
-         int bulbs;
-         int value;
-         
-         if (nplayers <= amount) {
-           break;
-         }
-          
-         turns = 9999;
-         bulbs = 0;
-         players_iterate(aplayer) {
-           int potential = aplayer->bulbs_last_turn
-                           + city_list_size(aplayer->cities) + 1;
-           if (tech_exists(pimpr->obsolete_by)) {
-             turns = MIN(turns, 
-               total_bulbs_required_for_goal(aplayer, pimpr->obsolete_by)
-               / (potential + 1));
-           }
-           if (players_on_same_team(aplayer, pplayer)) {
-             continue;
-           }
-           bulbs += potential;
-         } players_iterate_end;
-  
-         /* For some number of turns we will be receiving bulbs for free
-          * Bulbs should be amortized properly for each turn.
-          * We use formula for the sum of geometric series:
-          */
-         value = bulbs * (1.0 - pow(1.0 - (1.0 / MORT), turns)) * MORT;
-         
-         value = value  * (100 - game.info.freecost)     
-                 * (nplayers - amount) / (nplayers * amount * 100);
-         
-         /* WAG */
-         value /= 3;
-
-          CITY_LOG(LOG_DEBUG, pcity,
-                  "%s parasite effect: bulbs %d, turns %d, value %d", 
-                   get_improvement_name(id), bulbs, turns, value);
-       
-         v += value;
-         break;
+    if (active || n_needed_techs) {
+      const int v1 = improvement_effect_value(pplayer, gov, ai,
+                                             pcity, capital, 
+                                             pimpr, peffect,
+                                             cities[mypreq->range],
+                                             nplayers, v);
+      /* v1 could be negative (the effect could be undesirable),
+       * although it is usually positive.
+       * For example, in the default ruleset, Communism decreases the
+       * effectiveness of a Cathedral. */
+
+      if (active) {
+       v = v1;
+      } else { /* n_needed_techs */
+       /* We might want the technology that will enable this
+        * (additional) effect.
+        * The better the effect, the more we want the technology.
+        * Use (v1 - v) rather than v1 in case there are multiple
+        * effects that have technology requirements and to eliminate the
+        * 'base' effect of the building.
+         * We are more interested in (additional) effects that enhance
+        * buildings we already have.
+        */
+        const int a = already? 5: 4; /* WAG */
+        const int dv = (v1 - v) * a / (4 * n_needed_techs);
+       int t;
+       for (t = 0; t < n_needed_techs; t++) {
+         want_tech_for_improvement_effect(pplayer, pcity, pimpr->index,
+                                           needed_techs[t], dv);
        }
-       case EFT_GROWTH_FOOD:
-         v += c * 4 + (amount / 7) * pcity->surplus[O_FOOD];
-         break;
-       case EFT_AIRLIFT:
-         /* FIXME: We need some smart algorithm here. The below is 
-          * totally braindead. */
-         v += c + MIN(ai->stats.units.land, 13);
-         break;
-       case EFT_ANY_GOVERNMENT:
-         if (!can_change_to_government(pplayer, ai->goal.govt.gov)) {
-           v += MIN(MIN(ai->goal.govt.val, 65),
-               num_unknown_techs_for_goal(pplayer, ai->goal.govt.req) * 10);
-         }
-         break;
-       case EFT_ENABLE_NUKE:
-         /* Treat nuke as a Cruise Missile upgrade */
-         v += 20 + ai->stats.units.missiles * 5;
-         break;
-       case EFT_ENABLE_SPACE:
-         if (game.info.spacerace) {
-           v += 5;
-           if (ai->diplomacy.production_leader == pplayer) {
-             v += 100;
-           }
-         }
-         break;
-       case EFT_GIVE_IMM_TECH:
-         if (!ai_wants_no_science(pplayer)) {
-           v += amount * (game.info.sciencebox + 1);
-          }
-         break;
-       case EFT_HAVE_EMBASSIES:
-         v += 5 * nplayers;
-         break;
-       case EFT_REVEAL_CITIES:
-       case EFT_NO_ANARCHY:
-         break;  /* Useless for AI */
-       case EFT_NO_SINK_DEEP:
-         v += 15 + ai->stats.units.triremes * 5;
-         break;
-       case EFT_NUKE_PROOF:
-         if (ai->threats.nuclear) {
-           v += pcity->size * unit_list_size(ptile->units) * (capital + 1)
-                * amount / 100;
-         }
-         break;
-       case EFT_REVEAL_MAP:
-         if (!ai->explore.land_done || !ai->explore.sea_done) {
-           v += 10;
-         }
-         break;
-       case EFT_SIZE_UNLIMIT:
-         /* Note we look up the SIZE_UNLIMIT again right below.  This could
-          * be avoided... */
-         if (get_city_bonus(pcity, EFT_SIZE_UNLIMIT) == 0) {
-           amount = 20; /* really big city */
-         }
-         /* there not being a break here is deliberate, mind you */
-       case EFT_SIZE_ADJ:
-         if (get_city_bonus(pcity, EFT_SIZE_UNLIMIT) == 0) {
-           const int aqueduct_size = get_city_bonus(pcity, EFT_SIZE_ADJ);
-
-           if (!city_can_grow_to(pcity, pcity->size + 1)) {
-             v += pcity->surplus[O_FOOD] * ai->food_priority * amount;
-             if (pcity->size == aqueduct_size) {
-               v += 30 * pcity->surplus[O_FOOD];
-             }
-           }
-           v += c * amount * 4 / aqueduct_size;
-         }
-         break;
-       case EFT_SS_STRUCTURAL:
-       case EFT_SS_COMPONENT:
-       case EFT_SS_MODULE:
-         if (game.info.spacerace
-             /* If someone has started building spaceship already or
-              * we have chance to win a spacerace */
-             && (ai->diplomacy.spacerace_leader
-                 || ai->diplomacy.production_leader == pplayer)) {
-           v += 95;
-         }
-         break;
-       case EFT_SPY_RESISTANT:
-         /* Uhm, problem: City Wall has -50% here!! */
-         break;
-       case EFT_MOVE_BONUS:
-         /* FIXME: check other reqs (e.g., unitclass) */
-         v += (8 * v * amount + ai->stats.units.land
-               + ai->stats.units.sea + ai->stats.units.air);
-         break;
-       case EFT_UNIT_NO_LOSE_POP:
-         v += unit_list_size(ptile->units) * 2;
-         break;
-       case EFT_HP_REGEN:
-         /* FIXME: check other reqs (e.g., unitclass) */
-         v += (5 * c + ai->stats.units.land
-               + ai->stats.units.sea + ai->stats.units.air);
-         break;
-       case EFT_VETERAN_COMBAT:
-         /* FIXME: check other reqs (e.g., unitclass) */
-         v += (2 * c + ai->stats.units.land + ai->stats.units.sea
-               + ai->stats.units.air);
-         break;
-       case EFT_VETERAN_BUILD:
-         /* FIXME: check other reqs (e.g., unitclass, unitflag) */
-         v += (3 * c + ai->stats.units.land + ai->stats.units.sea
-               + ai->stats.units.air);
-         break;
-       case EFT_UPGRADE_UNIT:
-         v += ai->stats.units.upgradeable;
-         if (amount == 1) {
-           v *= 2;
-         } else if (amount == 2) {
-           v *= 3;
-         } else {
-           v *= 4;
-         }
-         break;
-       case EFT_DEFEND_BONUS:
-         if (ai_handicap(pplayer, H_DEFENSIVE)) {
-           v += amount / 10; /* make AI slow */
-         }
-         if (is_ocean(tile_get_terrain(pcity->tile))) {
-           v += ai->threats.ocean[-tile_get_continent(pcity->tile)]
-                ? amount/5 : amount/20;
-         } else {
-           adjc_iterate(pcity->tile, tile2) {
-             if (is_ocean(tile_get_terrain(tile2))) {
-               if (ai->threats.ocean[-tile_get_continent(tile2)]) {
-                 v += amount/5;
-                 break;
-               }
-             }
-           } adjc_iterate_end;
-         }
-         v += (amount/20 + ai->threats.invasions - 1) * c; /* for wonder */
-         if (ai->threats.continent[ptile->continent]
-             || capital
-             || (ai->threats.invasions
-                 && is_water_adjacent_to_tile(pcity->tile))) {
-           if (ai->threats.continent[ptile->continent]) {
-             v += amount;
-           } else {
-             v += amount / (!ai->threats.igwall ? (15 - capital * 5) : 15);
-           }
-         }
-         break;
-       case EFT_NO_INCITE:
-         if (get_city_bonus(pcity, EFT_NO_INCITE) <= 0) {
-           v += MAX((game.info.diplchance * 2 
-                      - game.info.incite_total_factor) / 2
-               - game.info.incite_improvement_factor * 5
-               - game.info.incite_unit_factor * 5, 0);
-         }
-         break;
-       case EFT_GAIN_AI_LOVE:
-         players_iterate(aplayer) {
-           if (aplayer->ai.control) {
-             if (ai_handicap(pplayer, H_DEFENSIVE)) {
-               v += amount / 10;
-             } else {
-               v += amount / 20;
-             }
-           }
-         } players_iterate_end;
-         break;
-        /* Currently not supported for building AI - wait for modpack users */
-        case EFT_UNHAPPY_FACTOR:
-        case EFT_UPKEEP_FACTOR:
-        case EFT_UNIT_UPKEEP_FREE_PER_CITY:
-        case EFT_CIVIL_WAR_CHANCE:
-        case EFT_EMPIRE_SIZE_MOD:
-        case EFT_EMPIRE_SIZE_STEP:
-        case EFT_MAX_RATES:
-        case EFT_MARTIAL_LAW_EACH:
-        case EFT_MARTIAL_LAW_MAX:
-        case EFT_RAPTURE_GROW:
-        case EFT_UNBRIBABLE_UNITS:
-        case EFT_REVOLUTION_WHEN_UNHAPPY:
-        case EFT_HAS_SENATE:
-        case EFT_INSPIRE_PARTISANS:
-        case EFT_HAPPINESS_TO_GOLD:
-        case EFT_FANATICS:
-        case EFT_NO_DIPLOMACY:
-        case EFT_OUTPUT_PENALTY_TILE:
-        case EFT_OUTPUT_INC_TILE_CELEBRATE:
-       case EFT_TRADE_REVENUE_BONUS:
-          break;
-       case EFT_LAST:
-         freelog(LOG_ERROR, "Bad effect type.");
-         break;
       }
     }
   } effect_list_iterate_end;
 
-  /* Reduce want if building gets obsoleted soon */
-  if (tech_exists(pimpr->obsolete_by)) {
-    v -= v / MAX(1, num_unknown_techs_for_goal(pplayer, pimpr->obsolete_by));
-  }
-
-  /* Adjust by building cost */
-  v -= (impr_build_shield_cost(pimpr->index)
-       / (pcity->surplus[O_SHIELD] * 10 + 1));
-
-  /* Would it mean losing shields? */
-  if ((pcity->production.is_unit 
-       || (is_wonder(pcity->production.value) 
-           && !is_wonder(id))
-       || (!is_wonder(pcity->production.value)
-           && is_wonder(id)))
-      && pcity->turn_last_built != game.info.turn) {
-    v -= (pcity->shield_stock / 2) * (SHIELD_WEIGHTING / 2);
-  }
+  if (already && tech_exists(pimpr->obsolete_by)) {
+    /* Discourage research of the technology that would make this building
+     * obsolete. The bigger the desire for this building, the more
+     * we want to discourage the technology. */
+    want_tech_for_improvement_effect(pplayer, pcity, pimpr->index,
+                                    pimpr->obsolete_by, -v);
+  } else if (!already) {
+    /* Increase the want for technologies that will enable
+     * construction of this improvement, if necessary.
+     */
+    const bool all_met = adjust_wants_for_reqs(pplayer, pcity, pimpr, v);
+    can_build = can_build && all_met;
+  }
+
+  if (is_coinage && can_build) {
+    /* Could have a negative want for coinage,
+     * if we have some stock in a building already. */
+    pcity->ai.building_want[pimpr->index] += v;
+  } else if (!already && can_build) {
+    /* Convert the base 'want' into a building want
+     * by applying various adjustments */
+
+    /* Would it mean losing shields? */
+    if ((pcity->production.is_unit 
+         || (is_wonder(pcity->production.value) && !is_wonder(pimpr->index))
+          || (!is_wonder(pcity->production.value) && is_wonder(pimpr->index)))
+        && pcity->turn_last_built != game.info.turn) {
+      v -= (pcity->shield_stock / 2) * (SHIELD_WEIGHTING / 2);
+    }
+
+    /* Reduce want if building gets obsoleted soon */
+    if (tech_exists(pimpr->obsolete_by)) {
+      v -= v / MAX(1, num_unknown_techs_for_goal(pplayer, pimpr->obsolete_by));
+    }
+
+    /* Are we wonder city? Try to avoid building non-wonders very much. */
+    if (pcity->id == ai->wonder_city && !is_wonder(pimpr->index)) {
+      v /= 5;
+    }
 
-  /* Are we wonder city? Try to avoid building non-wonders very much. */
-  if (pcity->id == ai->wonder_city && !is_wonder(id)) {
-    v /= 5;
+    /* Set */
+    pcity->ai.building_want[pimpr->index] += v;
   }
-
-  /* Set */
-  pcity->ai.building_want[id] = v;
+  /* Else we either have the improvement already,
+   * or we can not build it (yet) */
 }
 
 /**************************************************************************
@@ -794,6 +1015,106 @@
 }
 
 /************************************************************************** 
+  Whether the AI should calculate the building wants for this city
+  this turn, ahead of schedule.
+
+  Always recalculate if the city just finished building,
+  so we can make a sensible choice for the next thing to build.
+  Perhaps the improvement we were building has become obsolete,
+  or a different player built the Great Wonder we were building.
+**************************************************************************/
+static bool should_force_recalc(struct city *pcity)
+{
+  return city_built_last_turn(pcity) ||
+        (!pcity->production.is_unit
+         && !impr_flag(pcity->production.value, IF_GOLD)
+         && !can_eventually_build_improvement(pcity, pcity->production.value));
+}
+
+/************************************************************************** 
+  Calculate how much an AI player should want to build particular
+  improvements, because of the effects of those improvements, and
+  increase the want for technologies that will enable buildings with
+  desirable effects.
+**************************************************************************/
+static void adjust_wants_by_effects(struct player *pplayer,
+                                    struct city *wonder_city)
+{
+  /* Clear old building wants.
+   * Do this separately from the iteration over improvement types
+   * because each iteration could actually update more than one improvement,
+   * if improvements have improvements as requirements.
+   */
+  city_list_iterate(pplayer->cities, pcity) {
+    if (pplayer->ai.control && pcity->ai.next_recalc <= game.info.turn) {
+      /* Do a scheduled recalculation this turn */
+      impr_type_iterate(id) {
+        pcity->ai.building_want[id] = 0;
+      } impr_type_iterate_end;
+    } else if (pplayer->ai.control && should_force_recalc(pcity)) {
+      /* Do an emergency recalculation this turn. */
+      pcity->ai.recalc_interval = pcity->ai.next_recalc - game.info.turn;
+      pcity->ai.next_recalc = game.info.turn;
+
+      impr_type_iterate(id) {
+        pcity->ai.building_want[id] = 0;
+      } impr_type_iterate_end;
+    }
+  } city_list_iterate_end;
+
+  impr_type_iterate(id) {
+    /* Handle coinage specially because you can never complete coinage */
+    const bool is_coinage = impr_flag(id, IF_GOLD);
+    if (is_coinage || can_player_eventually_build_improvement(pplayer, id)) {
+      const bool is_wonder_impr = is_wonder(id);
+      struct impr_type *pimpr = get_improvement_type(id);
+
+      city_list_iterate(pplayer->cities, pcity) {
+        if (pcity != wonder_city && is_wonder_impr) {
+          /* Only wonder city should build wonders! */
+          pcity->ai.building_want[id] = 0;
+        } else if ((!is_coinage
+                    && !can_eventually_build_improvement(pcity, id))
+                   || is_building_replaced(pcity, id)) {
+          /* Don't consider impossible or redundant buildings */
+          pcity->ai.building_want[id] = 0;
+        } else if (pplayer->ai.control
+                   && pcity->ai.next_recalc <= game.info.turn) {
+          /* Building wants vary relatively slowly, so not worthwhile
+           * recalculating them every turn.
+           * We DO want to calculate (tech) wants because of buildings
+           * we already have. */
+          const bool already = city_got_building(pcity, id);
+
+          adjust_wants_by_effects1(pplayer, pcity, pimpr, already);
+
+          assert(!(already && 0 < pcity->ai.building_want[id]));
+        } else if (city_got_building(pcity, id)) {
+          /* Never want to build something we already have. */
+          pcity->ai.building_want[id] = 0;
+        }
+        /* else wait until a later turn */
+      } city_list_iterate_end;
+    } else {
+      /* An impossible improvement */
+      city_list_iterate(pplayer->cities, pcity) {
+        pcity->ai.building_want[id] = 0;
+      } city_list_iterate_end;
+    }
+  } impr_type_iterate_end;
+
+#if 0
+  /* This logging is relatively expensive, so activate only if necessary */
+  city_list_iterate(pplayer->cities, pcity) {
+    impr_type_iterate(id) {
+      CITY_LOG(LOG_DEBUG, pcity, "want to build %s with %d", 
+               get_improvement_name(id), pcity->ai.building_want[id]);
+    } impr_type_iterate_end;
+  } city_list_iterate_end;
+#endif
+}
+
+/************************************************************************** 
   Prime pcity->ai.building_want[]
 **************************************************************************/
 void ai_manage_buildings(struct player *pplayer)
@@ -872,39 +1193,15 @@
     acity->ai.worth = city_want(pplayer, acity, ai, B_LAST);
   } city_list_iterate_end;
 
-  impr_type_iterate(id) {
-    if (!can_player_build_improvement(pplayer, id)
-        || improvement_obsolete(pplayer, id)) {
-      continue;
-    }
-    city_list_iterate(pplayer->cities, pcity) {
-      if (pcity != wonder_city && is_wonder(id)) {
-        /* Only wonder city should build wonders! */
-        continue;
-      }
-      if (pplayer->ai.control && pcity->ai.next_recalc > game.info.turn) {
-        continue; /* do not recalc yet */
-      } else {
-        pcity->ai.building_want[id] = 0; /* do recalc */
-      }
-      if (city_got_building(pcity, id)
-          || !can_build_improvement(pcity, id)
-          || is_building_replaced(pcity, id)) {
-        continue; /* Don't build redundant buildings */
-      }
-      adjust_building_want_by_effects(pcity, id);
-      CITY_LOG(LOG_DEBUG, pcity, "want to build %s with %d", 
-               get_improvement_name(id), pcity->ai.building_want[id]);
-    } city_list_iterate_end;
-  } impr_type_iterate_end;
+  adjust_wants_by_effects(pplayer, wonder_city);
 
   /* Reset recalc counter */
   city_list_iterate(pplayer->cities, pcity) {
     if (pcity->ai.next_recalc <= game.info.turn) {
       /* This will spread recalcs out so that no one turn end is 
        * much longer than others */
-      pcity->ai.next_recalc = game.info.turn + myrand(RECALC_SPEED) 
-                              + RECALC_SPEED;
+      pcity->ai.recalc_interval = myrand(RECALC_SPEED) + RECALC_SPEED;
+      pcity->ai.next_recalc = game.info.turn + pcity->ai.recalc_interval;
     }
   } city_list_iterate_end;
 }
diff -ruN -Xvendor.freeciv.current/diff_ignore 
vendor.freeciv.current/common/city.c freeciv.PR12682/common/city.c
--- vendor.freeciv.current/common/city.c        2005-12-19 22:41:45.000000000 
+0000
+++ freeciv.PR12682/common/city.c       2005-12-26 12:22:41.000000000 +0000
@@ -2439,6 +2439,7 @@
   pcity->ai.invasion = 0;
   pcity->ai.bcost = 0;
   pcity->ai.attack = 0;
+  pcity->ai.recalc_interval = 1;
   pcity->ai.next_recalc = 0;
 
   memset(pcity->surplus, 0, O_COUNT * sizeof(*pcity->surplus));
diff -ruN -Xvendor.freeciv.current/diff_ignore 
vendor.freeciv.current/common/city.h freeciv.PR12682/common/city.h
--- vendor.freeciv.current/common/city.h        2005-12-19 22:41:45.000000000 
+0000
+++ freeciv.PR12682/common/city.h       2005-12-26 12:22:41.000000000 +0000
@@ -160,7 +160,9 @@
 
 struct ai_city {
   /* building desirabilities - easiest to handle them here -- Syela */
-  int building_want[B_LAST];    /* not sure these will always be < 256 */
+  /* The units of building_want seem to be production
+   * (shields/gold/luxuries) */
+  int building_want[B_LAST];
 
   unsigned int danger;          /* danger to be compared to assess_defense */
   bool diplomat_threat;         /* enemy diplomat or spy is near the city */
@@ -194,7 +196,9 @@
                       * all units coming to kill us. */
 
   int worth; /* Cache city worth here, sum of all weighted incomes */
-  int next_recalc; /* Only recalc every Nth turn */
+  /* Only recalc every Nth turn: */
+  int recalc_interval; /* Use for weighting values calculated every Nth turn */
+  int next_recalc;
 };
 
 struct city {
diff -ruN -Xvendor.freeciv.current/diff_ignore 
vendor.freeciv.current/common/player.h freeciv.PR12682/common/player.h
--- vendor.freeciv.current/common/player.h      2005-12-19 22:41:45.000000000 
+0000
+++ freeciv.PR12682/common/player.h     2005-12-26 12:22:41.000000000 +0000
@@ -100,6 +100,7 @@
   int prev_gold;
   int maxbuycost;
   int est_upkeep; /* estimated upkeep of buildings in cities */
+  /* The units of tech_want seem to be shields */
   int tech_want[A_LAST+1];
   int handicap;                        /* sum of enum handicap_type */
   int skill_level;             /* 0-10 value for save/load/display */

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