Multiple GEORADIUS bugs fixed.

By grepping the continuous integration errors log a number of GEORADIUS
tests failures were detected.

Fortunately when a GEORADIUS failure happens, the test suite logs enough
information in order to reproduce the problem: the PRNG seed,
coordinates and radius of the query.

By reproducing the issues, three different bugs were discovered and
fixed in this commit. This commit also improves the already good
reporting of the fuzzer and adds the failure vectors as regression
tests.

The issues found:

1. We need larger squares around the poles in order to cover the area
requested by the user. There were already checks in order to use a
smaller step (larger squares) but the limit set (+/- 67 degrees) is not
enough in certain edge cases, so 66 is used now.

2. Even near the equator, when the search area center is very near the
edge of the square, the north, south, west or ovest square may not be
able to fully cover the specified radius. Now a test is performed at the
edge of the initial guessed search area, and larger squares are used in
case the test fails.

3. Because of rounding errors between Redis and Tcl, sometimes the test
signaled false positives. This is now addressed.

Whenever possible the original code was improved a bit in other ways. A
debugging example stanza was added in order to make the next debugging
session simpler when the next bug is found.

5 files changed, 120 insertions, 19 deletions

diff --git a/src/debugmacro.h b/src/debugmacro.h
new file mode 100644
index 000000000..df237bad3
--- /dev/null
+++ b/src/debugmacro.h
@@ -0,0 +1,41 @@
+/* This file contains debugging macros to be used when investigating issues.
+ *
+ * -----------------------------------------------------------------------------
+ *
+ * Copyright (c) 2016, Salvatore Sanfilippo <antirez at gmail dot com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   * Redistributions of source code must retain the above copyright notice,
+ *     this list of conditions and the following disclaimer.
+ *   * Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *   * Neither the name of Redis nor the names of its contributors may be used
+ *     to endorse or promote products derived from this software without
+ *     specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <stdio.h>
+#define D(...)                                                               \
+    do {                                                                     \
+        FILE *fp = fopen("/tmp/log.txt","a");                                \
+        fprintf(fp,"%s:%s:%d:\t", __FILE__, __FUNCTION__, __LINE__);         \
+        fprintf(fp,__VA_ARGS__);                                             \
+        fprintf(fp,"\n");                                                    \
+        fclose(fp);                                                          \
+    } while (0);
diff --git a/src/geo.c b/src/geo.c
index 28cb433dc..331d22435 100644
--- a/src/geo.c
+++ b/src/geo.c
@@ -1,6 +1,6 @@
 /*
  * Copyright (c) 2014, Matt Stancliff <matt@genges.com>.
- * Copyright (c) 2015, Salvatore Sanfilippo <antirez@gmail.com>.
+ * Copyright (c) 2015-2016, Salvatore Sanfilippo <antirez@gmail.com>.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -30,6 +30,7 @@
 
 #include "geo.h"
 #include "geohash_helper.h"
+#include "debugmacro.h"
 
 /* Things exported from t_zset.c only for geo.c, since it is the only other
  * part of Redis that requires close zset introspection. */
diff --git a/src/geohash.c b/src/geohash.c
index a5e1dffbf..1ae7a7e05 100644
--- a/src/geohash.c
+++ b/src/geohash.c
@@ -1,7 +1,7 @@
 /*
  * Copyright (c) 2013-2014, yinqiwen <yinqiwen@gmail.com>
  * Copyright (c) 2014, Matt Stancliff <matt@genges.com>.
- * Copyright (c) 2015, Salvatore Sanfilippo <antirez@gmail.com>.
+ * Copyright (c) 2015-2016, Salvatore Sanfilippo <antirez@gmail.com>.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -118,7 +118,7 @@ void geohashGetCoordRange(GeoHashRange *long_range, GeoHashRange *lat_range) {
     lat_range->min = GEO_LAT_MIN;
 }
 
-int geohashEncode(GeoHashRange *long_range, GeoHashRange *lat_range,
+int geohashEncode(const GeoHashRange *long_range, const GeoHashRange *lat_range,
                   double longitude, double latitude, uint8_t step,
                   GeoHashBits *hash) {
     /* Check basic arguments sanity. */
diff --git a/src/geohash.h b/src/geohash.h
index c2f57bed0..ed2ef9336 100644
--- a/src/geohash.h
+++ b/src/geohash.h
@@ -95,7 +95,7 @@ typedef struct {
  * -1:failed
  */
 void geohashGetCoordRange(GeoHashRange *long_range, GeoHashRange *lat_range);
-int geohashEncode(GeoHashRange *long_range, GeoHashRange *lat_range,
+int geohashEncode(const GeoHashRange *long_range, const GeoHashRange *lat_range,
                   double longitude, double latitude, uint8_t step,
                   GeoHashBits *hash);
 int geohashEncodeType(double longitude, double latitude,
diff --git a/src/geohash_helper.c b/src/geohash_helper.c
index a65759bc4..139bcea11 100644
--- a/src/geohash_helper.c
+++ b/src/geohash_helper.c
@@ -1,7 +1,7 @@
 /*
  * Copyright (c) 2013-2014, yinqiwen <yinqiwen@gmail.com>
  * Copyright (c) 2014, Matt Stancliff <matt@genges.com>.
- * Copyright (c) 2015, Salvatore Sanfilippo <antirez@gmail.com>.
+ * Copyright (c) 2015-2016, Salvatore Sanfilippo <antirez@gmail.com>.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -36,6 +36,7 @@
 
 #include "fmacros.h"
 #include "geohash_helper.h"
+#include "debugmacro.h"
 #include <math.h>
 
 #define D_R (M_PI / 180.0)
@@ -56,8 +57,8 @@ const double MERCATOR_MIN = -20037726.37;
 static inline double deg_rad(double ang) { return ang * D_R; }
 static inline double rad_deg(double ang) { return ang / D_R; }
 
-/* You must *ONLY* estimate steps when you are encoding.
- * If you are decoding, always decode to GEO_STEP_MAX (26). */
+/* This function is used in order to estimate the step (bits precision)
+ * of the 9 search area boxes during radius queries. */
 uint8_t geohashEstimateStepsByRadius(double range_meters, double lat) {
     if (range_meters == 0) return 26;
     int step = 1;
@@ -65,12 +66,15 @@ uint8_t geohashEstimateStepsByRadius(double range_meters, double lat) {
         range_meters *= 2;
         step++;
     }
-    step -= 2; /* Make sure range is included in the worst case. */
+    step -= 2; /* Make sure range is included in most of the base cases. */
+
     /* Wider range torwards the poles... Note: it is possible to do better
      * than this approximation by computing the distance between meridians
      * at this latitude, but this does the trick for now. */
-    if (lat > 67 || lat < -67) step--;
-    if (lat > 80 || lat < -80) step--;
+    if (lat > 66 || lat < -66) {
+        step--;
+        if (lat > 80 || lat < -80) step--;
+    }
 
     /* Frame to valid range. */
     if (step < 1) step = 1;
@@ -105,12 +109,14 @@ int geohashBoundingBox(double longitude, double latitude, double radius_meters,
     return 1;
 }
 
+/* Return a set of areas (center + 8) that are able to cover a range query
+ * for the specified position and radius. */
 GeoHashRadius geohashGetAreasByRadius(double longitude, double latitude, double radius_meters) {
     GeoHashRange long_range, lat_range;
-    GeoHashRadius radius = {{0}};
-    GeoHashBits hash = {0,0};
-    GeoHashNeighbors neighbors = {{0}};
-    GeoHashArea area = {{0}};
+    GeoHashRadius radius;
+    GeoHashBits hash;
+    GeoHashNeighbors neighbors;
+    GeoHashArea area;
     double min_lon, max_lon, min_lat, max_lat;
     double bounds[4];
     int steps;
@@ -123,12 +129,65 @@ GeoHashRadius geohashGetAreasByRadius(double longitude, double latitude, double
 
     steps = geohashEstimateStepsByRadius(radius_meters,latitude);
 
-    geohashGetCoordRange(&long_range, &lat_range);
-    geohashEncode(&long_range, &lat_range, longitude, latitude, steps, &hash);
-    geohashNeighbors(&hash, &neighbors);
-    geohashGetCoordRange(&long_range, &lat_range);
-    geohashDecode(long_range, lat_range, hash, &area);
+    geohashGetCoordRange(&long_range,&lat_range);
+    geohashEncode(&long_range,&lat_range,longitude,latitude,steps,&hash);
+    geohashNeighbors(&hash,&neighbors);
+    geohashDecode(long_range,lat_range,hash,&area);
+
+    /* Check if the step is enough at the limits of the covered area.
+     * Sometimes when the search area is near an edge of the
+     * area, the estimated step is not small enough, since one of the
+     * north / south / west / east square is too near to the search area
+     * to cover everything. */
+    int decrease_step = 0;
+    {
+        GeoHashArea north, south, east, west;
+
+        geohashDecode(long_range, lat_range, neighbors.north, &north);
+        geohashDecode(long_range, lat_range, neighbors.south, &south);
+        geohashDecode(long_range, lat_range, neighbors.east, &east);
+        geohashDecode(long_range, lat_range, neighbors.west, &west);
+
+        if (geohashGetDistance(longitude,latitude,longitude,north.latitude.max)
+            < radius_meters) decrease_step = 1;
+        if (geohashGetDistance(longitude,latitude,longitude,south.latitude.min)
+            < radius_meters) decrease_step = 1;
+        if (geohashGetDistance(longitude,latitude,east.longitude.max,latitude)
+            < radius_meters) decrease_step = 1;
+        if (geohashGetDistance(longitude,latitude,west.longitude.min,latitude)
+            < radius_meters) decrease_step = 1;
+    }
+
+    if (decrease_step) {
+        steps--;
+        geohashEncode(&long_range,&lat_range,longitude,latitude,steps,&hash);
+        geohashNeighbors(&hash,&neighbors);
+        geohashDecode(long_range,lat_range,hash,&area);
+    }
+
+    /* Example debug info. This turns to be very useful every time there is
+     * to investigate radius search potential bugs. So better to leave it
+     * here. */
+    if (0) {
+        GeoHashArea myarea = {{0}};
+        geohashDecode(long_range, lat_range, neighbors.west, &myarea);
+
+        /* Dump West. */
+        D("Neighbors");
+        D("area.longitude.min: %f\n", myarea.longitude.min);
+        D("area.longitude.max: %f\n", myarea.longitude.max);
+        D("area.latitude.min: %f\n", myarea.latitude.min);
+        D("area.latitude.max: %f\n", myarea.latitude.max);
+
+        /* Dump center square. */
+        D("Area");
+        D("area.longitude.min: %f\n", area.longitude.min);
+        D("area.longitude.max: %f\n", area.longitude.max);
+        D("area.latitude.min: %f\n", area.latitude.min);
+        D("area.latitude.max: %f\n", area.latitude.max);
+    }
 
+    /* Exclude the search areas that are useless. */
     if (area.latitude.min < min_lat) {
         GZERO(neighbors.south);
         GZERO(neighbors.south_west);