text: #include <math.h>
  #include <postgres.h>
  #include <fmgr.h>
  
  Datum
  maptile_for_point(PG_FUNCTION_ARGS)
  {
     double lat = PG_GETARG_INT64(0) / 10000000.0;
     double lon = PG_GETARG_INT64(1) / 10000000.0;
     int zoom = PG_GETARG_INT32(2);
     double scale = pow(2, zoom);
     double r_per_d = M_PI / 180;
     unsigned int x;
     unsigned int y;
  
     x = floor((lon + 180.0) * scale / 360.0);
     y = floor((1 - log(tan(lat * r_per_d) + 1.0 / cos(lat * r_per_d)) / M_PI) * scale / 2.0);
  
     PG_RETURN_INT32((x << zoom) | y);
  }
  
  PG_FUNCTION_INFO_V1(maptile_for_point);
  
  /*
   * To bind this into PGSQL, try something like:
   *
   * CREATE FUNCTION maptile_for_point(int8, int8, int4) RETURNS int4
   *  AS '/path/to/rails-port/db/functions/libpgosm', 'maptile_for_point'
   *  LANGUAGE C STRICT;
   *
   * (without all the *s)
   */
  
  #ifdef PG_MODULE_MAGIC
  PG_MODULE_MAGIC;
  #endif
  