Function RunTileLoop

src/landscape.cpp:798–836

* Gradually iterate over all tiles on the map, calling their TileLoopProcs once every TILE_UPDATE_FREQUENCY ticks. */

 * Gradually iterate over all tiles on the map, calling their TileLoopProcs once every TILE_UPDATE_FREQUENCY ticks.
 */
void RunTileLoop()
{
	PerformanceAccumulator framerate(PFE_GL_LANDSCAPE);

	/* The pseudorandom sequence of tiles is generated using a Galois linear feedback
	 * shift register (LFSR). This allows a deterministic pseudorandom ordering, but
	 * still with minimal state and fast iteration. */

	/* Maximal length LFSR feedback terms, from 12-bit (for 64x64 maps) to 24-bit (for 4096x4096 maps).
	 * Extracted from http://www.ece.cmu.edu/~koopman/lfsr/ */
	static const uint32_t feedbacks[] = {
		0xD8F, 0x1296, 0x2496, 0x4357, 0x8679, 0x1030E, 0x206CD, 0x403FE, 0x807B8, 0x1004B2, 0x2006A8, 0x4004B2, 0x800B87
	};
	static_assert(lengthof(feedbacks) == 2 * MAX_MAP_SIZE_BITS - 2 * MIN_MAP_SIZE_BITS + 1);
	const uint32_t feedback = feedbacks[Map::LogX() + Map::LogY() - 2 * MIN_MAP_SIZE_BITS];

	/* We update every tile every TILE_UPDATE_FREQUENCY ticks, so divide the map size by 2^TILE_UPDATE_FREQUENCY_LOG = TILE_UPDATE_FREQUENCY */
	static_assert(2 * MIN_MAP_SIZE_BITS >= TILE_UPDATE_FREQUENCY_LOG);
	uint count = 1 << (Map::LogX() + Map::LogY() - TILE_UPDATE_FREQUENCY_LOG);

	TileIndex tile = _cur_tileloop_tile;
	/* The LFSR cannot have a zeroed state. */
	assert(tile != 0);

	/* Manually update tile 0 every TILE_UPDATE_FREQUENCY ticks - the LFSR never iterates over it itself.  */
	if (TimerGameTick::counter % TILE_UPDATE_FREQUENCY == 0) {
		_tile_type_procs[GetTileType(0)]->tile_loop_proc(TileIndex{});
		count--;
	}

	while (count--) {
		_tile_type_procs[GetTileType(tile)]->tile_loop_proc(tile);

		/* Get the next tile in sequence using a Galois LFSR. */
		tile = TileIndex{(tile.base() >> 1) ^ (-(int32_t)(tile.base() & 1) & feedback)};
	}

	_cur_tileloop_tile = tile;
}

void InitializeLandscape()
{