bool move_stair(coord_def stair_pos, bool away, bool allow_under);

static bool _move_stair(coord_def stair_pos, bool away)

bool move_stair(coord_def stair_pos, bool away, bool allow_under)

    if (!allow_under)
        ASSERT(stair_pos != you.pos());

        if (stair_pos == you.pos())

        if (allow_under && stair_pos == you.pos())

        if (_move_stair(stairs_avail[i], true))

        if (move_stair(stairs_avail[i], true, true))

static void _move_stair(coord_def stair_pos, bool away)
{
    ASSERT(stair_pos != you.pos());
    dungeon_feature_type feat = grd(stair_pos);
    ASSERT(grid_stair_direction(feat) != CMD_NO_CMD);
    coord_def begin, towards;
    if (away)
    {
        begin   = you.pos();
        towards = stair_pos;
    }
    else
    {
        // Can't move towards player if it's already adjacent.
        if (adjacent(you.pos(), stair_pos))
            return;
        begin   = stair_pos;
        towards = you.pos();
    }
    ray_def ray;
    if (!find_ray(begin, towards, ray))
    {
        mpr("Couldn't find ray between player and stairs.", MSGCH_ERROR);
        return;
    }
    // Don't start off under the player.
    if (away)
        ray.advance();
    bool found_stairs = false;
    int  past_stairs  = 0;
    while ( in_bounds(ray.pos()) && see_grid(ray.pos())
            && !grid_is_solid(ray.pos()) && ray.pos() != you.pos() )
    {
        if (ray.pos() == stair_pos)
            found_stairs = true;
        if (found_stairs)
            past_stairs++;
        ray.advance();
    }
    past_stairs--;
    if (!away && grid_is_solid(ray.pos()))
        // Transparent wall between stair and player.
        return;
    if (away && !found_stairs)
    {
        if (grid_is_solid(ray.pos()))
            // Transparent wall between stair and player.
            return;
        mpr("Ray didn't cross stairs.", MSGCH_ERROR);
    }
    if (away && past_stairs <= 0)
        // Stairs already at edge, can't move further away.
        return;
    if (!in_bounds(ray.pos()) || ray.pos() == you.pos())
        ray.regress();
    while (!see_grid(ray.pos()) || grd(ray.pos()) != DNGN_FLOOR)
    {
        ray.regress();
        if (!in_bounds(ray.pos()) || ray.pos() == you.pos()
            || ray.pos() == stair_pos)
        {
            // No squares in path are a plain floor.
            return;
        }
    }
    ASSERT(stair_pos != ray.pos());
    std::string stair_str =
        feature_description(stair_pos, false, DESC_CAP_THE, false);
    mprf("%s slides %s you!", stair_str.c_str(),
         away ? "away from" : "towards");
    // Animate stair moving.
    const feature_def &feat_def = get_feature_def(feat);
    bolt beam;

    beam.range   = INFINITE_DISTANCE;
    beam.flavour = BEAM_VISUAL;
    beam.type    = feat_def.symbol;
    beam.colour  = feat_def.colour;
    beam.source  = stair_pos;
    beam.target  = ray.pos();
    beam.name    = "STAIR BEAM";
    beam.draw_delay = 50; // Make beam animation slower than normal.
    beam.aimed_at_spot = true;
    beam.fire();
    // Clear out "missile trails"
    viewwindow(true, false);
    if (!swap_features(stair_pos, ray.pos(), false, false))
    {
        mprf(MSGCH_ERROR, "_move_stair(): failed to move %s",
             stair_str.c_str());
    }
}

        _move_stair(stairs_avail[i], stair_draw_count % 2);

        move_stair(stairs_avail[i], stair_draw_count % 2, false);