update geohash decode, 300% faster now

ardb.conf

@@ -401,26 +401,26 @@ check_type_before_set_string  0
 # Hashes are encoded using a memory efficient data structure when they have a
 # small number of entries, and the biggest entry does not exceed a given
 # threshold. These thresholds can be configured using the following directives.
-hash-max-ziplist-entries 128
-hash-max-ziplist-value 64
+hash-max-ziplist-entries 256
+hash-max-ziplist-value   256
 
 # Similarly to hashes, small lists are also encoded in a special way in order
 # to save a lot of space. The special representation is only used when
 # you are under the following limits:
-list-max-ziplist-entries 128
-list-max-ziplist-value 64
+list-max-ziplist-entries 256
+list-max-ziplist-value   256
 
 # Similarly to hashes and lists, sorted sets are also specially encoded in
 # order to save a lot of space. This encoding is only used when the length and
 # elements of a sorted set are below the following limits:
-set-max-ziplist-entries 128
-set-max-ziplist-value 64
+set-max-ziplist-entries 256
+set-max-ziplist-value   256
 
 # Similarly to hashes and lists, sorted sets are also specially encoded in
 # order to save a lot of space. This encoding is only used when the length and
 # elements of a sorted set are below the following limits:
-zset-max-ziplist-entries 128
-zset-max-ziplist-value 64
+zset-max-ziplist-entries 256
+zset-max-ziplist-value   256
 
 # Experiment: L1 cahce is the high level LRU cache holded in memory.
 # Use 'CACHE LOAD key' to load a key in L1 cache, 'CACHE EVICT key' to evict one, 'CACHE STATUS key' to view status for a key.

src/common/geo/geohash.c

@@ -243,16 +243,13 @@ int geohash_fast_decode(GeoHashRange lat_range, GeoHashRange lon_range, GeoHashB
     uint32_t ilato = xyhilo;        //get back the original integer coordinates
     uint32_t ilono = xyhilo >> 32;
 
-    //double lat_offset=ilato;
-    //double lon_offset=ilono;
-    //lat_offset /= (1<<step);
-    //lon_offset /= (1<<step);
-
-    //the ldexp call converts the integer to a double,then divides by 2**step to get the 0-1 coordinate, which is then multiplied times scale and added to the min to get the absolute coordinate
-    area->latitude.min = lat_range.min + ldexp(ilato, -step) * lat_scale;
-    area->latitude.max = lat_range.min + ldexp(ilato + 1, -step) * lat_scale;
-    area->longitude.min = lon_range.min + ldexp(ilono, -step) * lon_scale;
-    area->longitude.max = lon_range.min + ldexp(ilono + 1, -step) * lon_scale;
+    /*
+     * much faster than 'ldexp'
+     */
+    area->latitude.min = lat_range.min + (ilato * 1.0 / (1ull << step)) * lat_scale;
+    area->latitude.max = lat_range.min + ((ilato + 1) * 1.0 / (1ull << step)) * lat_scale;
+    area->longitude.min = lon_range.min + (ilono * 1.0 / (1ull << step)) * lon_scale;
+    area->longitude.max = lon_range.min + ((ilono + 1) * 1.0 / (1ull << step)) * lon_scale;
 
     return 0;
 }