-CREATE FUNCTION public.tile_for_point(integer, integer) RETURNS bigint
- LANGUAGE c STRICT
- AS '$libdir/libpgosm', 'tile_for_point';
+CREATE FUNCTION public.tile_for_point(scaled_lat integer, scaled_lon integer) RETURNS bigint
+ LANGUAGE plpgsql IMMUTABLE
+ AS $$
+DECLARE
+ x int8; -- quantized x from lon,
+ y int8; -- quantized y from lat,
+BEGIN
+ x := round(((scaled_lon / 10000000.0) + 180.0) * 65535.0 / 360.0);
+ y := round(((scaled_lat / 10000000.0) + 90.0) * 65535.0 / 180.0);
+
+ -- these bit-masks are special numbers used in the bit interleaving algorithm.
+ -- see https://graphics.stanford.edu/~seander/bithacks.html#InterleaveBMN
+ -- for the original algorithm and more details.
+ x := (x | (x << 8)) & 16711935; -- 0x00FF00FF
+ x := (x | (x << 4)) & 252645135; -- 0x0F0F0F0F
+ x := (x | (x << 2)) & 858993459; -- 0x33333333
+ x := (x | (x << 1)) & 1431655765; -- 0x55555555
+
+ y := (y | (y << 8)) & 16711935; -- 0x00FF00FF
+ y := (y | (y << 4)) & 252645135; -- 0x0F0F0F0F
+ y := (y | (y << 2)) & 858993459; -- 0x33333333
+ y := (y | (y << 1)) & 1431655765; -- 0x55555555
+
+ RETURN (x << 1) | y;
+END;
+$$;