Add geohashing capabilities

.travis.yml

@@ -16,7 +16,7 @@ env:
 before_script:
   - phpize
   - EXTRA_LDFLAGS="-precious-files-regex .libs/geospatial.gcno" LDFLAGS="-lgcov" CFLAGS="-Wall -ggdb3 -fno-strict-aliasing -coverage -O0" ./configure --enable-geospatial
-  - make -j 5 test && if ls tests/*.diff >/dev/null 2>&1; then echo "Tests failed" && exit 1; fi
+  - make -j 5 test && if ls tests/*.diff >/dev/null 2>&1; then echo "Tests failed" && cat tests/*.diff && exit 1; fi
   - gcov --object-directory .libs *.c
   - bash <(curl -s https://codecov.io/bash)
 

README.rst

@@ -170,3 +170,29 @@ you would use::
 	$point2 = [ 'type' => 'Point', 'coordinates' => [ 15, 10 ] ];
 
 	var_dump(fraction_along_gc_line($point1, $point2, 0.25));
+
+Geohashing
+----------
+
+The `geohash_encode` function can be used to convert GeoJSON Point to a geohash of a specific lenth (in this case, 12)::
+
+    echo geohash_encode(array('type' => 'Point', 'coordinates' => [16.4, 48.2]), 12);
+
+Which outputs::
+
+    u2edjnw17enr
+
+Similarly, a hashed geopoint can be decoded using `geohash_decode` function::
+
+    var_dump(geohash_decode('u2edjnw17enr'));
+    array(2) {
+      ["type"]=>
+      string(5) "Point"
+      ["coordinates"]=>
+      array(2) {
+        [0]=>
+        float(16.40000006184)
+        [1]=>
+        float(48.199999993667)
+      }
+    }

config.m4

@@ -5,5 +5,5 @@ PHP_ARG_ENABLE(geospatial, whether to enable geospatial support,
 [  --enable-geospatial           Enable geospatial support])
 
 if test "$PHP_GEOSPATIAL" != "no"; then
-  PHP_NEW_EXTENSION(geospatial, geospatial.c geo_array.c, $ext_shared)
+  PHP_NEW_EXTENSION(geospatial, geospatial.c geo_array.c geohash.c, $ext_shared)
 fi

geo_array.c

@@ -19,6 +19,8 @@
   +----------------------------------------------------------------------+
 */
 
+#ifndef PHP_GEO_ARRAY_H
+#define PHP_GEO_ARRAY_H
 #include <stdlib.h>
 
 #include "geo_array.h"
@@ -59,3 +61,4 @@ void geo_array_dtor(geo_array *points)
 	free(points->y);
 	free(points);
 }
+#endif /* PHP_GEO_ARRAY_H */

geo_lat_long.h

@@ -0,0 +1,28 @@
+/*
+  +----------------------------------------------------------------------+
+  | PHP Version 7                                                        |
+  +----------------------------------------------------------------------+
+  | Copyright (c) 2017 The PHP Group                                     |
+  +----------------------------------------------------------------------+
+  | This source file is subject to version 3.01 of the PHP license,      |
+  | that is bundled with this package in the file LICENSE, and is        |
+  | available through the world-wide-web at the following url:           |
+  | http://www.php.net/license/3_01.txt                                  |
+  | If you did not receive a copy of the PHP license and are unable to   |
+  | obtain it through the world-wide-web, please send a note to          |
+  | license@php.net so we can mail you a copy immediately.               |
+  +----------------------------------------------------------------------+
+  | Authors: Emir Beganovic <emir@php.net>                               |
+  +----------------------------------------------------------------------+
+*/
+
+#ifndef PHP_GEO_LAT_LONG_H
+#define PHP_GEO_LAT_LONG_H
+
+typedef struct {
+   double   x;
+   double   y;
+   double   z;
+} geo_lat_long;
+
+#endif

geohash.c

@@ -0,0 +1,146 @@
+/*
+  +----------------------------------------------------------------------+
+  | PHP Version 7                                                        |
+  +----------------------------------------------------------------------+
+  | Copyright (c) 2017 The PHP Group                                     |
+  +----------------------------------------------------------------------+
+  | This source file is subject to version 3.01 of the PHP license,      |
+  | that is bundled with this package in the file LICENSE, and is        |
+  | available through the world-wide-web at the following url:           |
+  | http://www.php.net/license/3_01.txt                                  |
+  | If you did not receive a copy of the PHP license and are unable to   |
+  | obtain it through the world-wide-web, please send a note to          |
+  | license@php.net so we can mail you a copy immediately.               |
+  +----------------------------------------------------------------------+
+  | Authors: Emir Beganovic <emir@php.net>                               |
+  +----------------------------------------------------------------------+
+*/
+
+#include <stdlib.h>
+
+#include "php.h"
+#include "geo_lat_long.h"
+#include "geohash.h"
+
+#define MAX_LAT  90.0
+#define MIN_LAT  -90.0
+
+#define MAX_LONG 180.0
+#define MIN_LONG -180.0
+
+typedef struct interval_string {
+    double high;
+    double low;
+} interval_struct;
+
+static char char_map[32] = "0123456789bcdefghjkmnpqrstuvwxyz";
+
+char* php_geo_geohash_encode(double latitude, double longitude, int precision)
+{
+    char* hash;
+    int steps;
+    double coord, mid;
+    int is_even = 1;
+    unsigned int hash_char = 0;
+    int i;
+    interval_struct lat_interval = { MAX_LAT, MIN_LAT };
+    interval_struct lng_interval = { MAX_LONG, MIN_LONG };
+    interval_struct* interval;
+
+    hash = (char*)safe_emalloc(precision, sizeof(char), 1);
+
+    hash[precision] = '\0';
+    steps = precision * 5.0;
+
+    for (i = 1; i <= steps; i++) {
+        if (is_even) {
+            interval = &lng_interval;
+            coord = longitude;
+        } else {
+            interval = &lat_interval;
+            coord = latitude;
+        }
+
+        mid = (interval->low + interval->high) / 2.0;
+        hash_char = hash_char << 1;
+
+        if (coord > mid) {
+            interval->low = mid;
+            hash_char |= 0x01;
+        } else {
+            interval->high = mid;
+        }
+
+        if (!(i % 5)) {
+            hash[(i - 1) / 5] = char_map[hash_char];
+            hash_char = 0;
+        }
+
+        is_even = !is_even;
+    }
+
+    return hash;
+}
+
+static unsigned int index_for_char(char c, char* string)
+{
+    unsigned int index = -1;
+    int string_amount = strlen(string);
+    int i;
+
+    for (i = 0; i < string_amount; i++) {
+        if (c == string[i]) {
+            index = i;
+            break;
+        }
+    }
+
+    return index;
+}
+
+geo_lat_long php_geo_geohash_decode(char* hash)
+{
+    geo_lat_long coordinate;
+    int char_amount = strlen(hash);
+
+    if (char_amount) {
+
+        int charmap_index;
+        double delta;
+        int i, j;
+
+        interval_struct lat_interval = { MAX_LAT, MIN_LAT };
+        interval_struct lng_interval = { MAX_LONG, MIN_LONG };
+        interval_struct* interval;
+
+        int is_even = 1;
+
+        for (i = 0; i < char_amount; i++) {
+
+            charmap_index = index_for_char(hash[i], (char*)char_map);
+
+            /* Interpret the last 5 bits of the integer */
+            for (j = 0; j < 5; j++) {
+                interval = is_even ? &lng_interval : &lat_interval;
+
+                delta = (interval->high - interval->low) / 2.0;
+
+                if ((charmap_index << j) & 0x0010) {
+                    interval->low += delta;
+                } else {
+                    interval->high -= delta;
+                }
+
+                is_even = !is_even;
+            }
+        }
+
+        coordinate.x = lat_interval.high - ((lat_interval.high - lat_interval.low) / 2.0);
+        coordinate.y = lng_interval.high - ((lng_interval.high - lng_interval.low) / 2.0);
+        coordinate.z = 0;
+    }
+
+    return coordinate;
+}
+
+/* }}} */

geohash.h

@@ -0,0 +1,33 @@
+/*
+  +----------------------------------------------------------------------+
+  | PHP Version 5/7                                                      |
+  +----------------------------------------------------------------------+
+  | Copyright (c) 2017 The PHP Group                                     |
+  +----------------------------------------------------------------------+
+  | This source file is subject to version 3.01 of the PHP license,      |
+  | that is bundled with this package in the file LICENSE, and is        |
+  | available through the world-wide-web at the following url:           |
+  | http://www.php.net/license/3_01.txt                                  |
+  | If you did not receive a copy of the PHP license and are unable to   |
+  | obtain it through the world-wide-web, please send a note to          |
+  | license@php.net so we can mail you a copy immediately.               |
+  +----------------------------------------------------------------------+
+  | Authors: Emir Beganovic <emir@php.net>                               |
+  +----------------------------------------------------------------------+
+*/
+
+#ifndef PHP_GEOHASH_H
+#define PHP_GEOHASH_H
+
+char* php_geo_geohash_encode(double lat, double lng, int precision);
+geo_lat_long php_geo_geohash_decode(char* hash);
+#endif /* PHP_GEOHASH_H */
+
+/*
+ * Local variables:
+ * tab-width: 4
+ * c-basic-offset: 4
+ * End:
+ * vim600: noet sw=4 ts=4 fdm=marker
+ * vim<600: noet sw=4 ts=4
+ */