movement.c

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/****************************************************************************
 Freeciv - Copyright (C) 2004 - The Freeciv Team
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.
 
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
****************************************************************************/
 
#ifdef HAVE_CONFIG_H
#include <fc_config.h>
#endif
 
/* utility */
#include "bitvector.h"
#include "fcintl.h"
#include "log.h"
#include "shared.h"
#include "support.h"
 
/* common */
#include "astring.h"
#include "base.h"
#include "effects.h"
#include "fc_types.h"
#include "game.h"
#include "map.h"
#include "road.h"
#include "unit.h"
#include "unitlist.h"
#include "unittype.h"
#include "terrain.h"
 
#include "movement.h"
 
/************************************************************************/
int utype_move_rate(const struct unit_type *utype, const struct tile *ptile,
                    const struct player *pplayer, int veteran_level,
                    int hitpoints)
{
  const struct unit_class *uclass;
  const struct veteran_level *vlevel;
  int base_move_rate, move_rate;
  int min_speed;
 
  fc_assert_ret_val(utype != nullptr, 0);
  vlevel = utype_veteran_level(utype, veteran_level);
  fc_assert_ret_val(vlevel != nullptr, 0);
  uclass = utype_class(utype);
 
  base_move_rate = utype->move_rate + vlevel->move_bonus;
  move_rate = base_move_rate;
 
  if (uclass_has_flag(uclass, UCF_DAMAGE_SLOWS)) {
    /* Scale the MP based on how many HP the unit has. */
    move_rate = (move_rate * hitpoints) / utype->hp;
  }
 
  /* Add on effects bonus (Magellan's Expedition, Lighthouse,
   * Nuclear Power). */
  move_rate += (get_unittype_bonus(pplayer, ptile, utype, nullptr,
                                   EFT_MOVE_BONUS)
                * SINGLE_MOVE);
 
  /* Don't let the move_rate be less than min_speed unless the base_move_rate is
   * also less than min_speed. */
  min_speed = MIN(uclass->min_speed, base_move_rate);
  if (move_rate < min_speed) {
    move_rate = min_speed;
  }
 
  return move_rate;
}
 
/************************************************************************/
int unit_move_rate(const struct unit *punit)
{
  fc_assert_ret_val(NULL != punit, 0);
 
  return utype_move_rate(unit_type_get(punit), unit_tile(punit),
                         unit_owner(punit), punit->veteran, punit->hp);
}
 
/************************************************************************/
int utype_unknown_move_cost(const struct unit_type *utype)
{
  const struct unit_class *uclass = utype_class(utype);
  int move_cost;
  int worst_effect_mc;
 
  if (!uclass_has_flag(uclass, UCF_TERRAIN_SPEED)) {
    /* Unit is not subject to terrain movement costs. */
    move_cost = SINGLE_MOVE;
  } else if (utype_has_flag(utype, UTYF_IGTER)) {
    /* All terrain movement costs are equal! */
    move_cost = MOVE_COST_IGTER;
  } else {
    /* Unit is subject to terrain movement costs. */
    move_cost = 1; /* Arbitrary minimum. */
    terrain_type_iterate(pterrain) {
      if (is_native_to_class(uclass, pterrain, NULL)
          && pterrain->movement_cost > move_cost) {
        /* Exact movement cost matters only if we can enter
         * the tile. */
        move_cost = pterrain->movement_cost;
      }
    } terrain_type_iterate_end;
    move_cost *= SINGLE_MOVE; /* Real value. */
  }
 
  /* Move cost from effects. */
  worst_effect_mc = 0;
  action_by_result_iterate(paction, ACTRES_UNIT_MOVE) {
    struct universal req_pattern[] = {
      { .kind = VUT_ACTION, .value.action = paction },
      { .kind = VUT_UTYPE,  .value.utype = utype },
    };
    int max_effect_mc;
 
    if (!utype_can_do_action(utype, action_id(paction))) {
      /* Not relevant. */
      continue;
    }
 
    max_effect_mc = effect_cumulative_max(EFT_ACTION_SUCCESS_MOVE_COST,
                                          req_pattern, ARRAY_SIZE(req_pattern));
 
    if (max_effect_mc > worst_effect_mc) {
      worst_effect_mc = max_effect_mc;
    }
  } action_by_result_iterate_end;
  move_cost += worst_effect_mc;
 
  /* Let's see if we can cross over all terrain types, else apply a malus.
   * We want units that may encounter unsuitable terrain explore less.
   * N.B.: We don't take in account terrain no unit can enter here. */
  terrain_type_iterate(pterrain) {
    if (BV_ISSET_ANY(pterrain->native_to)
        && !is_native_to_class(uclass, pterrain, NULL)) {
      /* Units that may encounter unsuitable terrain explore less. */
      move_cost *= 2;
      break;
    }
  } terrain_type_iterate_end;
 
  return move_cost;
}
 
/************************************************************************/
bool unit_can_defend_here(const struct civ_map *nmap, const struct unit *punit)
{
  struct unit *ptrans = unit_transport_get(punit);
 
  if (ptrans == NULL) {
    /* FIXME: Redundant check; if unit is in the tile without transport
     *        it's known to be able to exist there. */
    return can_unit_exist_at_tile(nmap, punit, unit_tile(punit));
  }
 
  switch (unit_type_get(punit)->tp_defense) {
  case TDT_BLOCKED:
    return FALSE;
  case TDT_ALIGHT:
    return can_unit_exist_at_tile(nmap, punit, unit_tile(punit))
      && can_unit_deboard_or_be_unloaded(nmap, punit, ptrans);
  case TDT_ALWAYS:
    return TRUE;
  }
 
  fc_assert(FALSE);
 
  return FALSE;
}
 
/************************************************************************/
bool can_attack_non_native_hard_reqs(const struct unit_type *utype)
{
  return uclass_has_flag(utype_class(utype), UCF_ATTACK_NON_NATIVE)
         && !utype_has_flag(utype, UTYF_ONLY_NATIVE_ATTACK);
}
 
/************************************************************************/
bool can_attack_non_native(const struct unit_type *utype)
{
  return can_attack_non_native_hard_reqs(utype)
         && (utype_can_do_action_result(utype, ACTRES_ATTACK)
             || utype_can_do_action_result(utype, ACTRES_BOMBARD)
             || utype_can_do_action_result(utype, ACTRES_WIPE_UNITS)
             || utype_can_do_action_result(utype, ACTRES_NUKE_UNITS));
}
 
/************************************************************************/
bool can_attack_from_non_native(const struct unit_type *utype)
{
  return (utype_can_do_action_result_when_ustate(utype, ACTRES_ATTACK,
                                                 USP_NATIVE_TILE, FALSE)
          || utype_can_do_action_result_when_ustate(utype,
                                                    ACTRES_WIPE_UNITS,
                                                    USP_LIVABLE_TILE, FALSE)
          || utype_can_do_action_result_when_ustate(utype,
                                                    ACTRES_CONQUER_CITY,
                                                    USP_LIVABLE_TILE,
                                                    FALSE));
}
 
/************************************************************************/
bool is_city_channel_tile(const struct civ_map *nmap,
                          const struct unit_class *punitclass,
                          const struct tile *ptile,
                          const struct tile *pexclude)
{
  struct dbv tile_processed;
  struct tile_list *process_queue = tile_list_new();
  bool found = FALSE;
 
  dbv_init(&tile_processed, map_num_tiles());
  for (;;) {
    dbv_set(&tile_processed, tile_index(ptile));
    adjc_iterate(nmap, ptile, piter) {
      if (dbv_isset(&tile_processed, tile_index(piter))) {
        continue;
      } else if (piter != pexclude
                 && is_native_to_class(punitclass, tile_terrain(piter),
                                       tile_extras(piter))) {
        found = TRUE;
        break;
      } else if (piter != pexclude
                 && NULL != tile_city(piter)) {
        tile_list_append(process_queue, piter);
      } else {
        dbv_set(&tile_processed, tile_index(piter));
      }
    } adjc_iterate_end;
 
    if (found || 0 == tile_list_size(process_queue)) {
      break; /* No more tile to process. */
    } else {
      ptile = tile_list_front(process_queue);
      tile_list_pop_front(process_queue);
    }
  }
 
  dbv_free(&tile_processed);
  tile_list_destroy(process_queue);
 
  return found;
}
 
/************************************************************************/
bool can_exist_at_tile(const struct civ_map *nmap,
                       const struct unit_type *utype,
                       const struct tile *ptile)
{
  /* Cities are safe havens except for units in the middle of non-native
   * terrain. This can happen if adjacent terrain is changed after unit
   * arrived to city. */
  if (NULL != tile_city(ptile)
      && (uclass_has_flag(utype_class(utype), UCF_BUILD_ANYWHERE)
          || is_native_near_tile(nmap, utype_class(utype), ptile)
          || (1 == game.info.citymindist
              && is_city_channel_tile(nmap, utype_class(utype), ptile, NULL)))) {
    return TRUE;
  }
 
  /* UTYF_COAST_STRICT unit cannot exist in an ocean tile without access to land. */
  if (utype_has_flag(utype, UTYF_COAST_STRICT)
      && !is_safe_ocean(nmap, ptile)) {
    return FALSE;
  }
 
  return is_native_tile(utype, ptile);
}
 
/************************************************************************/
bool can_unit_exist_at_tile(const struct civ_map *nmap,
                            const struct unit *punit,
                            const struct tile *ptile)
{
  return can_exist_at_tile(nmap, unit_type_get(punit), ptile);
}
 
/************************************************************************/
bool is_native_tile(const struct unit_type *punittype,
                    const struct tile *ptile)
{
  return is_native_to_class(utype_class(punittype), tile_terrain(ptile),
                            tile_extras(ptile));
}
 
/************************************************************************/
bool is_native_to_class(const struct unit_class *punitclass,
                        const struct terrain *pterrain,
                        const bv_extras *extras)
{
  if (!pterrain) {
    /* Unknown is considered native terrain */
    return TRUE;
  }
 
  if (BV_ISSET(pterrain->native_to, uclass_index(punitclass))) {
    return TRUE;
  }
 
  if (extras != NULL) {
    extra_type_list_iterate(punitclass->cache.native_tile_extras, pextra) {
      if (BV_ISSET(*extras, extra_index(pextra))) {
        return TRUE;
      }
    } extra_type_list_iterate_end;
  }
 
  return FALSE;
}
 
 
/************************************************************************/
bool is_native_move(const struct civ_map *nmap,
                    const struct unit_class *punitclass,
                    const struct tile *src_tile,
                    const struct tile *dst_tile)
{
  const struct road_type *proad;
 
  if (is_native_to_class(punitclass, tile_terrain(dst_tile), NULL)) {
    /* We aren't using extras to make the destination native. */
    return TRUE;
  } else if (!is_native_tile_to_class(punitclass, src_tile)) {
    /* Disembarking or leaving port, so ignore road connectivity. */
    return TRUE;
  } else if (is_native_to_class(punitclass, tile_terrain(src_tile), NULL)) {
    /* Native source terrain depends entirely on destination tile nativity. */
    return is_native_tile_to_class(punitclass, dst_tile);
  }
 
  /* Check for non-road native extras on the source tile. */
  extra_type_list_iterate(punitclass->cache.native_tile_extras, pextra) {
    if (tile_has_extra(src_tile, pextra)
        && !is_extra_caused_by(pextra, EC_ROAD)
        && is_native_tile_to_class(punitclass, dst_tile)) {
      /* If there is one, and the destination is native, the move is native. */
      return TRUE;
    }
  } extra_type_list_iterate_end;
 
  extra_type_list_iterate(punitclass->cache.native_tile_extras, pextra) {
    if (!tile_has_extra(dst_tile, pextra)) {
      continue;
    } else if (!is_extra_caused_by(pextra, EC_ROAD)) {
      /* The destination is native because of a non-road extra. */
      return TRUE;
    }
 
    proad = extra_road_get(pextra);
 
    if (road_has_flag(proad, RF_JUMP_TO)) {
      extra_type_list_iterate(punitclass->cache.native_tile_extras, jextra) {
        if (pextra != jextra
            && is_extra_caused_by(jextra, EC_ROAD)
            && tile_has_extra(src_tile, jextra)
            && road_has_flag(jextra->data.road, RF_JUMP_FROM)) {
          return TRUE;
        }
      } extra_type_list_iterate_end;
    }
 
    extra_type_list_iterate(proad->integrators, iextra) {
      if (!tile_has_extra(src_tile, iextra)) {
        continue;
      }
      if (ALL_DIRECTIONS_CARDINAL()) {
        /* move_mode does not matter as all of them accept cardinal move */
        return TRUE;
      }
      switch (extra_road_get(iextra)->move_mode) {
      case RMM_FAST_ALWAYS:
        /* Road connects source and destination, so we're fine. */
        return TRUE;
      case RMM_CARDINAL:
        /* Road connects source and destination if cardinal move. */
        if (is_move_cardinal(nmap, src_tile, dst_tile)) {
          return TRUE;
        }
        break;
      case RMM_RELAXED:
        if (is_move_cardinal(nmap, src_tile, dst_tile)) {
          /* Cardinal moves have no between tiles, so connected. */
          return TRUE;
        }
        cardinal_between_iterate(nmap, src_tile, dst_tile, between) {
          if (tile_has_extra(between, iextra)
              || (pextra != iextra && tile_has_extra(between, pextra))) {
            /* We have a link for the connection.
             * 'pextra != iextra' is there just to avoid tile_has_extra()
             * in by far more common case that 'pextra == iextra' */
            return TRUE;
          }
        } cardinal_between_iterate_end;
        break;
      }
    } extra_type_list_iterate_end;
  } extra_type_list_iterate_end;
 
  return FALSE;
}
 
/************************************************************************/
bool is_native_near_tile(const struct civ_map *nmap,
                         const struct unit_class *uclass,
                         const struct tile *ptile)
{
  if (is_native_tile_to_class(uclass, ptile)) {
    return TRUE;
  }
 
  adjc_iterate(nmap, ptile, ptile2) {
    if (is_native_tile_to_class(uclass, ptile2)) {
      return TRUE;
    }
  } adjc_iterate_end;
 
  return FALSE;
}
 
/************************************************************************/
bool can_unit_survive_at_tile(const struct civ_map *nmap,
                              const struct unit *punit,
                              const struct tile *ptile)
{
  const struct unit_type *utype;
 
  if (!can_unit_exist_at_tile(nmap, punit, ptile)) {
    return FALSE;
  }
 
  if (tile_city(ptile)) {
    return TRUE;
  }
 
  utype = unit_type_get(punit);
  if (tile_has_refuel_extra(ptile, utype_class(utype))) {
    /* Unit can always survive at refueling base */
    return TRUE;
  }
 
  if (utype_has_flag(utype, UTYF_COAST) && is_safe_ocean(nmap, ptile)) {
    /* Refueling coast */
    return TRUE;
  }
 
  if (utype_fuel(utype)) {
    /* Unit requires fuel and this is not refueling tile */
    return FALSE;
  }
 
  if (is_losing_hp(punit)) {
    /* Unit is losing HP over time in this tile (no city or native base) */
    return FALSE;
  }
 
  return TRUE;
}
 
 
/************************************************************************/
bool can_step_taken_wrt_to_zoc(const struct unit_type *punittype,
                               const struct player *unit_owner,
                               const struct tile *src_tile,
                               const struct tile *dst_tile,
                               const struct civ_map *zmap)
{
  if (unit_type_really_ignores_zoc(punittype)) {
    return TRUE;
  }
  if (is_allied_unit_tile(dst_tile, unit_owner)) {
    return TRUE;
  }
  if (tile_city(src_tile) || tile_city(dst_tile)) {
    return TRUE;
  }
  if (terrain_has_flag(tile_terrain(src_tile), TER_NO_ZOC)
      || terrain_has_flag(tile_terrain(dst_tile), TER_NO_ZOC)) {
    return TRUE;
  }
 
  return (is_my_zoc(unit_owner, src_tile, zmap)
          || is_my_zoc(unit_owner, dst_tile, zmap));
}
 
/************************************************************************/
bool unit_can_move_to_tile(const struct civ_map *nmap,
                           const struct unit *punit,
                           const struct tile *dst_tile,
                           bool igzoc,
                           bool enter_transport,
                           bool enter_enemy_city)
{
  return (MR_OK == unit_move_to_tile_test(nmap, punit,
                                          punit->activity, unit_tile(punit),
                                          dst_tile, igzoc,
                                          enter_transport, NULL,
                                          enter_enemy_city));
}
 
/************************************************************************/
bool unit_can_teleport_to_tile(const struct civ_map *nmap,
                               const struct unit *punit,
                               const struct tile *dst_tile,
                               bool enter_transport,
                               bool enter_enemy_city)
{
  return (MR_OK == unit_teleport_to_tile_test(nmap, punit, punit->activity,
                                              unit_tile(punit), dst_tile,
                                              enter_transport, NULL,
                                              enter_enemy_city));
}
 
/************************************************************************/
enum unit_move_result
unit_move_to_tile_test(const struct civ_map *nmap,
                       const struct unit *punit,
                       enum unit_activity activity,
                       const struct tile *src_tile,
                       const struct tile *dst_tile, bool igzoc,
                       bool enter_transport, struct unit *embark_to,
                       bool enter_enemy_city)
{
  bool zoc;
  struct city *pcity;
  const struct unit_type *punittype = unit_type_get(punit);
  const struct player *puowner = unit_owner(punit);
 
  /* 1) */
  if (activity != ACTIVITY_IDLE
      && activity != ACTIVITY_GOTO) {
    /* For other activities the unit must be stationary. */
    return MR_BAD_ACTIVITY;
  }
 
  /* 2) */
  if (punit->stay) {
    return MR_UNIT_STAY;
  }
 
  /* 3) */
  if ((!is_server() || game.server.random_move_time != puowner)
      && utype_has_flag(punittype, UTYF_RANDOM_MOVEMENT)) {
    return MR_RANDOM_ONLY;
  }
 
  /* 4) */
  if (!is_tiles_adjacent(src_tile, dst_tile)) {
    /* Of course you can only move to adjacent positions. */
    return MR_BAD_DESTINATION;
  }
 
  /* 5) */
  if (is_non_allied_unit_tile(dst_tile, puowner,
                              utype_has_flag(punittype, UTYF_FLAGLESS))) {
    /* You can't move onto a tile with non-allied units on it (try
     * attacking instead). */
    return MR_DESTINATION_OCCUPIED_BY_NON_ALLIED_UNIT;
  }
 
  /* 6) */
  if (puowner->ai_common.barbarian_type == ANIMAL_BARBARIAN
      && dst_tile->terrain->animal != punittype) {
    return MR_ANIMAL_DISALLOWED;
  }
 
  /* 7) */
  if (embark_to != NULL) {
    if (!could_unit_load(punit, embark_to)) {
      return MR_NO_TRANSPORTER_CAPACITY;
    }
  } else if (!(can_exist_at_tile(nmap, punittype, dst_tile)
               || (enter_transport
                   && unit_could_load_at(punit, dst_tile)))) {
    return MR_NO_TRANSPORTER_CAPACITY;
  }
 
  /* 8) */
  if (is_non_attack_unit_tile(dst_tile, puowner)) {
    /* You can't move into a non-allied tile.
     *
     * FIXME: this should never happen since it should be caught by check
     * #5. */
    return MR_NO_WAR;
  }
 
  /* 9) */
  if ((pcity = tile_city(dst_tile))) {
    if (enter_enemy_city) {
      if (pplayers_non_attack(city_owner(pcity), puowner)) {
        /* You can't move into an empty city of a civilization you're at
         * peace with - you must first either declare war or make an
         * alliance. */
        return MR_NO_WAR;
      }
    } else {
      if (!pplayers_allied(city_owner(pcity), puowner)) {
        /* You can't move into an empty city of a civilization you're not
         * allied to. Assume that the player tried to attack. */
        return MR_NO_WAR;
      }
    }
  }
 
  /* 10) */
  zoc = igzoc
    || can_step_taken_wrt_to_zoc(punittype, puowner, src_tile, dst_tile, nmap);
  if (!zoc) {
    /* The move is illegal because of zones of control. */
    return MR_ZOC;
  }
 
  /* 11) */
  if (utype_has_flag(punittype, UTYF_COAST_STRICT)
      && !pcity && !is_safe_ocean(nmap, dst_tile)) {
    return MR_TRIREME;
  }
 
  /* 12) */
  if (!utype_has_flag(punittype, UTYF_CIVILIAN)
      && !player_can_invade_tile(puowner, dst_tile)) {
    return MR_PEACE;
  }
 
  /* 13) */
  if (unit_transported(punit)
     && !can_unit_unload(punit, unit_transport_get(punit))) {
    return MR_CANNOT_DISEMBARK;
  }
 
  /* 14) */
  if (!(is_native_move(nmap, utype_class(punittype), src_tile, dst_tile)
        /* Allow non-native moves into cities or boarding transport. */
        || pcity
        || unit_could_load_at(punit, dst_tile))) {
    return MR_NON_NATIVE_MOVE;
  }
 
  return MR_OK;
}
 
/************************************************************************/
enum unit_move_result
unit_teleport_to_tile_test(const struct civ_map *nmap,
                           const struct unit *punit,
                           enum unit_activity activity,
                           const struct tile *src_tile,
                           const struct tile *dst_tile,
                           bool enter_transport, struct unit *embark_to,
                           bool enter_enemy_city)
{
  struct city *pcity;
  const struct unit_type *punittype = unit_type_get(punit);
  const struct player *puowner = unit_owner(punit);
 
  /* 1) */
  if (is_non_allied_unit_tile(dst_tile, puowner,
                              utype_has_flag(punittype, UTYF_FLAGLESS))) {
    /* You can't move onto a tile with non-allied units on it (try
     * attacking instead). */
    return MR_DESTINATION_OCCUPIED_BY_NON_ALLIED_UNIT;
  }
 
  /* 2) */
  if (puowner->ai_common.barbarian_type == ANIMAL_BARBARIAN
      && dst_tile->terrain->animal != punittype) {
    return MR_ANIMAL_DISALLOWED;
  }
 
  /* 3) */
  if (embark_to != NULL) {
    if (!could_unit_load(punit, embark_to)) {
      return MR_NO_TRANSPORTER_CAPACITY;
    }
  } else if (!(can_exist_at_tile(nmap, punittype, dst_tile)
               || (enter_transport
                   && unit_could_load_at(punit, dst_tile)))) {
    return MR_NO_TRANSPORTER_CAPACITY;
  }
 
  /* 4) */
  if (is_non_attack_unit_tile(dst_tile, puowner)) {
    /* You can't move into a non-allied tile.
     *
     * FIXME: this should never happen since it should be caught by check
     * #1. */
    return MR_NO_WAR;
  }
 
  /* 5) */
  if ((pcity = tile_city(dst_tile))) {
    if (enter_enemy_city) {
      if (pplayers_non_attack(city_owner(pcity), puowner)) {
        /* You can't move into an empty city of a civilization you're at
         * peace with - you must first either declare war or make an
         * alliance. */
        return MR_NO_WAR;
      }
    } else {
      if (!pplayers_allied(city_owner(pcity), puowner)) {
        /* You can't move into an empty city of a civilization you're not
         * allied to. Assume that the player tried to attack. */
        return MR_NO_WAR;
      }
    }
  }
 
  /* 6) */
  if (utype_has_flag(punittype, UTYF_COAST_STRICT)
      && !pcity && !is_safe_ocean(nmap, dst_tile)) {
    return MR_TRIREME;
  }
 
  /* 7) */
  if (!utype_has_flag(punittype, UTYF_CIVILIAN)
      && !player_can_invade_tile(puowner, dst_tile)) {
    return MR_PEACE;
  }
 
  return MR_OK;
}
 
/************************************************************************/
bool can_unit_transport(const struct unit *transporter,
                        const struct unit *transported)
{
  fc_assert_ret_val(transporter != NULL, FALSE);
  fc_assert_ret_val(transported != NULL, FALSE);
 
  return can_unit_type_transport(unit_type_get(transporter),
                                 unit_class_get(transported));
}
 
/************************************************************************/
bool can_unit_type_transport(const struct unit_type *transporter,
                             const struct unit_class *transported)
{
  if (transporter->transport_capacity <= 0) {
    return FALSE;
  }
 
  return BV_ISSET(transporter->cargo, uclass_index(transported));
}
 
/************************************************************************/
bool unit_can_load(const struct unit *punit)
{
  if (unit_transported(punit)) {
    /* In another transport already. Can it unload first? */
    if (!can_unit_unload(punit, punit->transporter)) {
      return FALSE;
    }
  }
 
  unit_list_iterate(unit_tile(punit)->units, ptransport) {
    /* could_unit_load() instead of can_unit_load() since latter
     * would check against unit already being transported, and we need
     * to support unload+load to a new transport. */
    if (ptransport != punit->transporter) {
      if (could_unit_load(punit, ptransport)) {
        return TRUE;
      }
    }
  } unit_list_iterate_end;
 
  return FALSE;
}
 
/************************************************************************/
bool unit_could_load_at(const struct unit *punit, const struct tile *ptile)
{
  unit_list_iterate(ptile->units, ptransport) {
    if (could_unit_load(punit, ptransport)) {
      return TRUE;
    }
  } unit_list_iterate_end;
 
  return FALSE;
}
 
static int move_points_denomlen = 0;
 
/************************************************************************/
void init_move_fragments(void)
{
  char denomstr[10];
  /* String length of maximum denominator for fractional representation of
   * movement points, for padding of text representation */
  fc_snprintf(denomstr, sizeof(denomstr), "%d", SINGLE_MOVE);
  move_points_denomlen = strlen(denomstr);
}
 
/************************************************************************/
const char *move_points_text_full(int mp, bool reduce, const char *prefix,
                                  const char *none, bool align)
{
  static struct astring str = ASTRING_INIT;
  int pad1, pad2;
 
  if (align && SINGLE_MOVE > 1) {
    /* Align to worst-case denominator even if we might be reducing to
     * lowest terms, as other entries in a table might not reduce */
    pad1 = move_points_denomlen;      /* numerator or denominator */
    pad2 = move_points_denomlen*2+2;  /* everything right of integer part */
  } else {
    /* If no possible fractional part, alignment unneeded even if requested */
    pad1 = pad2 = 0;
  }
  if (!prefix) {
    prefix = "";
  }
  astr_clear(&str);
  if ((mp == 0 && none) || SINGLE_MOVE == 0) {
    /* No movement points, and we have a special representation to use */
    /* (Also used when SINGLE_MOVE == 0, to avoid dividing by zero, which is
     * important for client before ruleset has been received. Doesn't much
     * matter what we print in this case.) */
    astr_add(&str, "%s%*s", none ? none : "", pad2, "");
  } else if ((mp % SINGLE_MOVE) == 0) {
    /* Integer move points */
    astr_add(&str, "%s%d%*s", prefix, mp / SINGLE_MOVE, pad2, "");
  } else {
    /* Fractional part */
    int cancel;
 
    fc_assert(SINGLE_MOVE > 1);
    if (reduce) {
      /* Reduce to lowest terms */
      int gcd = mp;
      /* Calculate greatest common divisor with Euclid's algorithm */
      int b = SINGLE_MOVE;
 
      while (b != 0) {
        int t = b;
        b = gcd % b;
        gcd = t;
      }
      cancel = gcd;
    } else {
      /* No cancellation */
      cancel = 1;
    }
    if (mp < SINGLE_MOVE) {
      /* Fractional move points */
      astr_add(&str, "%s%*d/%*d", prefix,
               pad1, (mp % SINGLE_MOVE) / cancel, pad1, SINGLE_MOVE / cancel);
    } else {
      /* Integer + fractional move points */
      astr_add(&str,
               "%s%d %*d/%*d", prefix, mp / SINGLE_MOVE,
               pad1, (mp % SINGLE_MOVE) / cancel, pad1, SINGLE_MOVE / cancel);
    }
  }
  return astr_str(&str);
}
 
/************************************************************************/
const char *move_points_text(int mp, bool reduce)
{
  return move_points_text_full(mp, reduce, NULL, NULL, FALSE);
}