summaryrefslogtreecommitdiff
path: root/src/geohash.c
blob: 2cbcf2875434418d6d57296202ad43eb8caa41a1 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
/*
 * Copyright (c) 2013-2014, yinqiwen <yinqiwen@gmail.com>
 * Copyright (c) 2014, Matt Stancliff <matt@genges.com>.
 * Copyright (c) 2015-2016, Salvatore Sanfilippo <antirez@gmail.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 "geohash.h"

/**
 * Hashing works like this:
 * Divide the world into 4 buckets.  Label each one as such:
 *  -----------------
 *  |       |       |
 *  |       |       |
 *  | 0,1   | 1,1   |
 *  -----------------
 *  |       |       |
 *  |       |       |
 *  | 0,0   | 1,0   |
 *  -----------------
 */

/* Interleave lower bits of x and y, so the bits of x
 * are in the even positions and bits from y in the odd;
 * x and y must initially be less than 2**32 (4294967296).
 * From:  https://graphics.stanford.edu/~seander/bithacks.html#InterleaveBMN
 */
static inline uint64_t interleave64(uint32_t xlo, uint32_t ylo) {
    static const uint64_t B[] = {0x5555555555555555ULL, 0x3333333333333333ULL,
                                 0x0F0F0F0F0F0F0F0FULL, 0x00FF00FF00FF00FFULL,
                                 0x0000FFFF0000FFFFULL};
    static const unsigned int S[] = {1, 2, 4, 8, 16};

    uint64_t x = xlo;
    uint64_t y = ylo;

    x = (x | (x << S[4])) & B[4];
    y = (y | (y << S[4])) & B[4];

    x = (x | (x << S[3])) & B[3];
    y = (y | (y << S[3])) & B[3];

    x = (x | (x << S[2])) & B[2];
    y = (y | (y << S[2])) & B[2];

    x = (x | (x << S[1])) & B[1];
    y = (y | (y << S[1])) & B[1];

    x = (x | (x << S[0])) & B[0];
    y = (y | (y << S[0])) & B[0];

    return x | (y << 1);
}

/* reverse the interleave process
 * derived from http://stackoverflow.com/questions/4909263
 */
static inline uint64_t deinterleave64(uint64_t interleaved) {
    static const uint64_t B[] = {0x5555555555555555ULL, 0x3333333333333333ULL,
                                 0x0F0F0F0F0F0F0F0FULL, 0x00FF00FF00FF00FFULL,
                                 0x0000FFFF0000FFFFULL, 0x00000000FFFFFFFFULL};
    static const unsigned int S[] = {0, 1, 2, 4, 8, 16};

    uint64_t x = interleaved;
    uint64_t y = interleaved >> 1;

    x = (x | (x >> S[0])) & B[0];
    y = (y | (y >> S[0])) & B[0];

    x = (x | (x >> S[1])) & B[1];
    y = (y | (y >> S[1])) & B[1];

    x = (x | (x >> S[2])) & B[2];
    y = (y | (y >> S[2])) & B[2];

    x = (x | (x >> S[3])) & B[3];
    y = (y | (y >> S[3])) & B[3];

    x = (x | (x >> S[4])) & B[4];
    y = (y | (y >> S[4])) & B[4];

    x = (x | (x >> S[5])) & B[5];
    y = (y | (y >> S[5])) & B[5];

    return x | (y << 32);
}

void geohashGetCoordRange(GeoHashRange *long_range, GeoHashRange *lat_range) {
    /* These are constraints from EPSG:900913 / EPSG:3785 / OSGEO:41001 */
    /* We can't geocode at the north/south pole. */
    long_range->max = GEO_LONG_MAX;
    long_range->min = GEO_LONG_MIN;
    lat_range->max = GEO_LAT_MAX;
    lat_range->min = GEO_LAT_MIN;
}

int geohashEncode(const GeoHashRange *long_range, const GeoHashRange *lat_range,
                  double longitude, double latitude, uint8_t step,
                  GeoHashBits *hash) {
    /* Check basic arguments sanity. */
    if (hash == NULL || step > 32 || step == 0 ||
        RANGEPISZERO(lat_range) || RANGEPISZERO(long_range)) return 0;

    /* Return an error when trying to index outside the supported
     * constraints. */
    if (longitude > GEO_LONG_MAX || longitude < GEO_LONG_MIN ||
        latitude > GEO_LAT_MAX || latitude < GEO_LAT_MIN) return 0;

    hash->bits = 0;
    hash->step = step;

    if (latitude < lat_range->min || latitude > lat_range->max ||
        longitude < long_range->min || longitude > long_range->max) {
        return 0;
    }

    double lat_offset =
        (latitude - lat_range->min) / (lat_range->max - lat_range->min);
    double long_offset =
        (longitude - long_range->min) / (long_range->max - long_range->min);

    /* convert to fixed point based on the step size */
    lat_offset *= (1ULL << step);
    long_offset *= (1ULL << step);
    hash->bits = interleave64(lat_offset, long_offset);
    return 1;
}

int geohashEncodeType(double longitude, double latitude, uint8_t step, GeoHashBits *hash) {
    GeoHashRange r[2] = {{0}};
    geohashGetCoordRange(&r[0], &r[1]);
    return geohashEncode(&r[0], &r[1], longitude, latitude, step, hash);
}

int geohashEncodeWGS84(double longitude, double latitude, uint8_t step,
                       GeoHashBits *hash) {
    return geohashEncodeType(longitude, latitude, step, hash);
}

int geohashDecode(const GeoHashRange long_range, const GeoHashRange lat_range,
                   const GeoHashBits hash, GeoHashArea *area) {
    if (HASHISZERO(hash) || NULL == area || RANGEISZERO(lat_range) ||
        RANGEISZERO(long_range)) {
        return 0;
    }

    area->hash = hash;
    uint8_t step = hash.step;
    uint64_t hash_sep = deinterleave64(hash.bits); /* hash = [LAT][LONG] */

    double lat_scale = lat_range.max - lat_range.min;
    double long_scale = long_range.max - long_range.min;

    uint32_t ilato = hash_sep;       /* get lat part of deinterleaved hash */
    uint32_t ilono = hash_sep >> 32; /* shift over to get long part of hash */

    /* divide by 2**step.
     * Then, for 0-1 coordinate, multiply times scale and add
       to the min to get the absolute coordinate. */
    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 =
        long_range.min + (ilono * 1.0 / (1ull << step)) * long_scale;
    area->longitude.max =
        long_range.min + ((ilono + 1) * 1.0 / (1ull << step)) * long_scale;

    return 1;
}

int geohashDecodeType(const GeoHashBits hash, GeoHashArea *area) {
    GeoHashRange r[2] = {{0}};
    geohashGetCoordRange(&r[0], &r[1]);
    return geohashDecode(r[0], r[1], hash, area);
}

int geohashDecodeWGS84(const GeoHashBits hash, GeoHashArea *area) {
    return geohashDecodeType(hash, area);
}

int geohashDecodeAreaToLongLat(const GeoHashArea *area, double *xy) {
    if (!xy) return 0;
    xy[0] = (area->longitude.min + area->longitude.max) / 2;
    if (xy[0] > GEO_LONG_MAX) xy[0] = GEO_LONG_MAX;
    if (xy[0] < GEO_LONG_MIN) xy[0] = GEO_LONG_MIN;
    xy[1] = (area->latitude.min + area->latitude.max) / 2;
    if (xy[1] > GEO_LAT_MAX) xy[1] = GEO_LAT_MAX;
    if (xy[1] < GEO_LAT_MIN) xy[1] = GEO_LAT_MIN;
    return 1;
}

int geohashDecodeToLongLatType(const GeoHashBits hash, double *xy) {
    GeoHashArea area = {{0}};
    if (!xy || !geohashDecodeType(hash, &area))
        return 0;
    return geohashDecodeAreaToLongLat(&area, xy);
}

int geohashDecodeToLongLatWGS84(const GeoHashBits hash, double *xy) {
    return geohashDecodeToLongLatType(hash, xy);
}

static void geohash_move_x(GeoHashBits *hash, int8_t d) {
    if (d == 0)
        return;

    uint64_t x = hash->bits & 0xaaaaaaaaaaaaaaaaULL;
    uint64_t y = hash->bits & 0x5555555555555555ULL;

    uint64_t zz = 0x5555555555555555ULL >> (64 - hash->step * 2);

    if (d > 0) {
        x = x + (zz + 1);
    } else {
        x = x | zz;
        x = x - (zz + 1);
    }

    x &= (0xaaaaaaaaaaaaaaaaULL >> (64 - hash->step * 2));
    hash->bits = (x | y);
}

static void geohash_move_y(GeoHashBits *hash, int8_t d) {
    if (d == 0)
        return;

    uint64_t x = hash->bits & 0xaaaaaaaaaaaaaaaaULL;
    uint64_t y = hash->bits & 0x5555555555555555ULL;

    uint64_t zz = 0xaaaaaaaaaaaaaaaaULL >> (64 - hash->step * 2);
    if (d > 0) {
        y = y + (zz + 1);
    } else {
        y = y | zz;
        y = y - (zz + 1);
    }
    y &= (0x5555555555555555ULL >> (64 - hash->step * 2));
    hash->bits = (x | y);
}

void geohashNeighbors(const GeoHashBits *hash, GeoHashNeighbors *neighbors) {
    neighbors->east = *hash;
    neighbors->west = *hash;
    neighbors->north = *hash;
    neighbors->south = *hash;
    neighbors->south_east = *hash;
    neighbors->south_west = *hash;
    neighbors->north_east = *hash;
    neighbors->north_west = *hash;

    geohash_move_x(&neighbors->east, 1);
    geohash_move_y(&neighbors->east, 0);

    geohash_move_x(&neighbors->west, -1);
    geohash_move_y(&neighbors->west, 0);

    geohash_move_x(&neighbors->south, 0);
    geohash_move_y(&neighbors->south, -1);

    geohash_move_x(&neighbors->north, 0);
    geohash_move_y(&neighbors->north, 1);

    geohash_move_x(&neighbors->north_west, -1);
    geohash_move_y(&neighbors->north_west, 1);

    geohash_move_x(&neighbors->north_east, 1);
    geohash_move_y(&neighbors->north_east, 1);

    geohash_move_x(&neighbors->south_east, 1);
    geohash_move_y(&neighbors->south_east, -1);

    geohash_move_x(&neighbors->south_west, -1);
    geohash_move_y(&neighbors->south_west, -1);
}