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redis/src/geohash.c

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/*
* Copyright (c) 2013-2014, yinqiwen <yinqiwen@gmail.com>
* Copyright (c) 2014, Matt Stancliff <matt@genges.com>.
* Copyright (c) 2015-current, Redis Ltd.
* 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);
}
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