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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include "mongo/db/jsobj.h"
#include "mongo/db/storage/key_string.h"
#include "mongo/platform/basic.h"
namespace mongo {
class GeoHash;
class Box;
struct Point;
std::ostream& operator<<(std::ostream& s, const GeoHash& h);
/* This class maps an unsigned x,y coordinate pair to a hash value.
* To hash values more interesting than unsigned, use the GeoHashConverter,
* which maps doubles to unsigned values.
*/
class GeoHash {
public:
static unsigned int const kMaxBits; // = 32;
GeoHash();
// The strings are binary values of length <= 64,
// examples: 1001010100101, 1
explicit GeoHash(const std::string& hash);
explicit GeoHash(const char* s);
// bits is how many bits are used to hash each of x and y.
GeoHash(unsigned x, unsigned y, unsigned bits = 32);
GeoHash(const GeoHash& old);
// hash is a raw hash value. we just copy these into our private fields.
GeoHash(long long hash, unsigned bits);
// This only works if e is BinData. To get a GeoHash from other BSONElements,
// use the converter class.
explicit GeoHash(const BSONElement& e, unsigned bits = 32);
// Convert from the hashed value to unsigned.
void unhash(unsigned* x, unsigned* y) const;
/** Is the 'bit'-th most significant bit set? (NOT the least significant) */
static bool isBitSet(unsigned val, unsigned bit);
/** Return a GeoHash with one bit of precision lost. */
GeoHash up() const;
bool hasPrefix(const GeoHash& other) const;
std::string toString() const;
std::string toStringHex1() const;
void setBit(unsigned pos, bool value);
bool getBit(unsigned pos) const;
bool getBitX(unsigned pos) const;
bool getBitY(unsigned pos) const;
// XXX: what does this really do?
BSONObj wrap(const char* name = "") const;
// XXX what does this do
bool constrains() const;
bool canRefine() const;
// XXX comment better
bool atMinX() const;
bool atMinY() const;
// XXX comment better
bool atMaxX() const;
bool atMaxY() const;
// XXX: what does this do
void move(int x, int y);
GeoHash& operator=(const GeoHash& h);
bool operator==(const GeoHash& h) const;
bool operator!=(const GeoHash& h) const;
bool operator<(const GeoHash& h) const;
// Append the hash in s to our current hash. We expect s to be '0' or '1' or '\0',
// though we also treat non-'1' values as '0'.
GeoHash& operator+=(const char* s);
GeoHash operator+(const char* s) const;
GeoHash operator+(const std::string& s) const;
// Append the minimum range of the hash to the builder provided (inclusive)
void appendHashMin(BSONObjBuilder* builder, const char* fieldName) const;
// Append the minimum range of the hash to the KeyString provided (inclusive)
void appendHashMin(KeyString::Builder* ks) const;
void appendHashMin(KeyString::PooledBuilder* ks) const;
// Append the maximum range of the hash to the builder provided (inclusive)
void appendHashMax(BSONObjBuilder* builder, const char* fieldName) const;
long long getHash() const;
unsigned getBits() const;
GeoHash commonPrefix(const GeoHash& other) const;
// If this is not a leaf cell, set children[0..3] to the four children of
// this cell (in traversal order) and return true. Otherwise returns false.
bool subdivide(GeoHash children[4]) const;
// Return true if the given cell is contained within this one.
bool contains(const GeoHash& other) const;
// Return the parent at given level.
GeoHash parent(unsigned int level) const;
GeoHash parent() const;
// Return the neighbors of closest vertex to this cell at the given level,
// by appending them to "output". Normally there are four neighbors, but
// the closest vertex may only have two or one neighbor if it is next to the
// boundary.
//
// Requires: level < this->_bits, so that we can determine which vertex is
// closest (in particular, level == kMaxBits is not allowed).
void appendVertexNeighbors(unsigned level, std::vector<GeoHash>* output) const;
// public but only for the purpose of testing
void unhash_fast(unsigned* x, unsigned* y) const;
void unhash_slow(unsigned* x, unsigned* y) const;
private:
// Create a hash from the provided string. Used by the std::string and char* cons.
void initFromString(const char* s);
/* Keep the upper _bits*2 bits of _hash, clear the lower bits.
* Maybe there's junk in there? XXX Not sure why this is done.
*/
void clearUnusedBits();
// XXX: what does this do
void _move(unsigned offset, int d);
long long _hash;
// Bits per field. Our hash is 64 bits, and we have an X and a Y field,
// so this is 1 to 32.
unsigned _bits;
};
/* Convert between various types and the GeoHash. We need additional information (scaling etc.)
* to convert to/from GeoHash. The additional information doesn't change often and is the same
* for all conversions, so we stick all the conversion methods here with their associated
* data.
*/
class GeoHashConverter {
public:
static double const kMachinePrecision; // = 1.1e-16
struct Parameters {
// How many bits to use for the hash?
int bits;
// X/Y values must be [min, max]
double min;
double max;
// Values are scaled by this when converted to/from hash scale.
double scaling;
};
/**
* Factory method to return a new instance with status. Uses hashing parameters parsed from a
* BSONObj.
*/
static StatusWith<std::unique_ptr<GeoHashConverter>> createFromDoc(const BSONObj& paramDoc);
/**
* Factory method to return a new instance with status.
*/
static StatusWith<std::unique_ptr<GeoHashConverter>> createFromParams(const Parameters& params);
static double calcUnhashToBoxError(const Parameters& params);
/**
* Return converter parameterss which can be used to
* construct an copy of this converter.
*/
const Parameters& getParams() const {
return _params;
}
int getBits() const {
return _params.bits;
}
double getError() const {
return _error;
}
double getErrorSphere() const {
return _errorSphere;
}
double getMin() const {
return _params.min;
}
double getMax() const {
return _params.max;
}
double distanceBetweenHashes(const GeoHash& a, const GeoHash& b) const;
/**
* Hashing functions. Convert the following types to a GeoHash:
* BSONElement
* BSONObj
* Point
* double, double
*/
GeoHash hash(const Point& p) const;
GeoHash hash(const BSONElement& e) const;
GeoHash hash(const BSONObj& o) const;
// src is printed out as debugging information. I'm not sure if it's actually
// somehow the 'source' of o? Anyway, this is nasty, very nasty. XXX
GeoHash hash(const BSONObj& o, const BSONObj* src) const;
GeoHash hash(double x, double y) const;
/** Unhashing functions.
* Convert from a hash to the following types:
* double, double
* Point
* Box
* BSONObj
*/
// XXX: these should have consistent naming
Point unhashToPoint(const GeoHash& h) const;
Point unhashToPoint(const BSONElement& e) const;
BSONObj unhashToBSONObj(const GeoHash& h) const;
void unhash(const GeoHash& h, double* x, double* y) const;
/**
* Generates bounding box from geohash, expanded by the error bound
*/
Box unhashToBoxCovering(const GeoHash& h) const;
double sizeOfDiag(const GeoHash& a) const;
// Return the sizeEdge of a cell at a given level.
double sizeEdge(unsigned level) const;
// Used by test.
double convertDoubleFromHashScale(double in) const;
double convertToDoubleHashScale(double in) const;
private:
GeoHashConverter(const Parameters& params);
void init();
// Convert from an unsigned in [0, (max-min)*scaling] to [min, max]
double convertFromHashScale(unsigned in) const;
// Convert from a double that is [min, max] to an unsigned in [0, (max-min)*scaling]
unsigned convertToHashScale(double in) const;
Parameters _params;
// We compute these based on the _params:
double _error;
double _errorSphere;
// Error bound of unhashToBox, see hash_test.cpp for its proof.
// 8 * max(|max|, |min|) * u
double _errorUnhashToBox;
};
} // namespace mongo
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