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/**
* Copyright (C) 2008-2012 10gen Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* 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 GNU Affero General 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/pch.h"
#include "mongo/db/jsobj.h"
#include <iostream>
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:
GeoHash();
// The strings are binary values of length <= 64,
// examples: 1001010100101, 1
explicit GeoHash(const 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;
string toString() const;
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 hash to the builder provided.
void appendToBuilder(BSONObjBuilder* b, const char * name) const;
long long getHash() const;
unsigned getBits() const;
GeoHash commonPrefix(const GeoHash& other) const;
private:
// XXX not sure why this is done exactly. Why does binary
// data need to be reversed? byte ordering of some sort?
static void _copyAndReverse(char *dst, const char *src);
// Create a hash from the provided string. Used by the 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);
// XXX: this is nasty and has no example
void unhash_fast(unsigned *x, unsigned *y) const;
void unhash_slow(unsigned *x, unsigned *y) const;
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:
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;
};
GeoHashConverter(const Parameters ¶ms);
/**
* 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 geo hash using converter.
* Used in GeoBrowse::fillStack and db/query/explain_plan.cpp
* to generate index bounds from
* geo hashes in plan stats.
*/
Box unhashToBox(const GeoHash &h) const;
double sizeOfDiag(const GeoHash& a) const;
// XXX: understand/clean this.
double sizeEdge(const GeoHash& a) const;
private:
// 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;
};
} // namespace mongo
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