+++ /dev/null
---------------------------------------------------------------------------------
--- SQL versions of the C database functions.
---
--- Pure pl/pgsql versions are *slower* than the C versions, and not recommended
--- for production use. However, they are significantly easier to install, and
--- require fewer dependencies.
---------------------------------------------------------------------------------
-
--- tile_for_point function returns a Morton-encoded integer representing a z16
--- tile which contains the given (scaled_lon, scaled_lat) coordinate. Note that
--- these are passed into the function as (lat, lon) and should be scaled by
--- 10^7.
---
--- The Morton encoding packs two dimensions down to one with fairly good
--- spatial locality, and can be used to index points without the need for a
--- proper 2D index.
-CREATE OR REPLACE FUNCTION tile_for_point(scaled_lat int4, scaled_lon int4)
- RETURNS int8
- AS $$
-DECLARE
- x int8; -- quantized x from lon,
- y int8; -- quantized y from lat,
-BEGIN
- x := round(((scaled_lon / 10000000.0) + 180.0) * 65535.0 / 360.0);
- y := round(((scaled_lat / 10000000.0) + 90.0) * 65535.0 / 180.0);
-
- -- these bit-masks are special numbers used in the bit interleaving algorithm.
- -- see https://graphics.stanford.edu/~seander/bithacks.html#InterleaveBMN
- -- for the original algorithm and more details.
- x := (x | (x << 8)) & 16711935; -- 0x00FF00FF
- x := (x | (x << 4)) & 252645135; -- 0x0F0F0F0F
- x := (x | (x << 2)) & 858993459; -- 0x33333333
- x := (x | (x << 1)) & 1431655765; -- 0x55555555
-
- y := (y | (y << 8)) & 16711935; -- 0x00FF00FF
- y := (y | (y << 4)) & 252645135; -- 0x0F0F0F0F
- y := (y | (y << 2)) & 858993459; -- 0x33333333
- y := (y | (y << 1)) & 1431655765; -- 0x55555555
-
- RETURN (x << 1) | y;
-END;
-$$ LANGUAGE plpgsql IMMUTABLE;
-
-
--- xid_to_int4 converts a PostgreSQL transaction ID (xid) to a 32-bit integer
--- which can then be used to efficiently find rows which have changed between
--- two given transactions. This is currently used by Osmosis to extract a
--- stream of edits for "diff replication" **HOWEVER** this is a pain point, as
--- (ab)using the xid in this way is _not_ supported or recommended by Postgres
--- devs. It is preventing us upgrading to PostgreSQL version 10+, and will
--- hopefully be replaced Real Soon Now.
---
--- From the Osmosis distribution by Brett Henderson:
--- https://github.com/openstreetmap/osmosis/blob/master/package/script/contrib/apidb_0.6_osmosis_xid_indexing.sql
-CREATE OR REPLACE FUNCTION xid_to_int4(t xid)
- RETURNS integer
- AS
-$$
-DECLARE
- tl bigint;
- ti int;
-BEGIN
- tl := t;
-
- IF tl >= 2147483648 THEN
- tl := tl - 4294967296;
- END IF;
-
- ti := tl;
-
- RETURN ti;
-END;
-$$ LANGUAGE 'plpgsql' IMMUTABLE STRICT;