Hash Class Reference

Hash is class that carries 160-bit digest. More...

#include <hash.h>

Public Member Functions
	Hash ()
	Hash (const quint32 aHash160bits[KNumberOfIntsInHash])
	Hash (const quint32 aBits1, const quint32 aBits2, const quint32 aBits3, const quint32 aBits4, const quint32 aBits5)
	Hash (const unsigned char aDigest[KNumberOfIntsInHash *4])
	Hash (const char *aHexString, int aHexStringLen)
	Hash (const QSslCertificate &aSslCert)
void	fromString (const unsigned char *aBuf)
QString	toString () const
void	fromQVariant (const QVariant &aQVariantHashValue)
QVariant	toQVariant () const
void	calculate (const QByteArray &aBuf)
bool	operator== (const Hash &aHashToCompare) const
bool	operator!= (const Hash &aHashToCompare) const
bool	operator< (const Hash &aHashToCompare) const
bool	operator> (const Hash &aHashToCompare) const
Hash &	operator= (const Hash &aHashToSubstitute)
Hash	distanceFrom (const Hash &aHash)
Hash	operator- (const Hash &aToBeSubstracted) const
Hash	operator+ (const Hash &aToBeAdded) const

Public Attributes
quint32	iHash160bits [KNumberOfIntsInHash]

Static Public Attributes
static const int	KNumberOfIntsInHash = 5

Private Member Functions
void	setFromCharArray (const unsigned char aDigest[KNumberOfIntsInHash *4])

Detailed Description

Hash is class that carries 160-bit digest.

Hash number class. This is usually an encryption key fingerprint or something returned by SHA1 function. The number that this class carries identifies an object inside classified ads, such objects as "classified ad", "user", "node", "attachment file" or anything that is present in the network. Here the hash is number between 0-2^160.

Constructor & Destructor Documentation

Hash() [1/6]

Hash::Hash

(

)

constructor. produces zero-value hash.

Hash() [2/6]

Hash::Hash

(

const quint32

aHash160bits[KNumberOfIntsInHash]

)

constructor.

Parameters

aHash160bits

is array of KNumberOfIntsInHash containing 32 bits each. The most-significant bits come in first, least-significant come in last. .. e.g. for constructing a hash that has value (decimal) 1 you say Hash(0,0,0,0,1).

Hash() [3/6]

Hash::Hash	(	const quint32	aBits1,
		const quint32	aBits2,
		const quint32	aBits3,
		const quint32	aBits4,
		const quint32	aBits5
	)

constructor.

Parameters

aBits1	most significant bits
aBits2	quite significant bits
aBits3	somewhat significant bits
aBits4	less significant bits
aBits5	least significant bits

Hash() [4/6]

Hash::Hash

(

const unsigned char

aDigest[KNumberOfIntsInHash *4]

)

constructor.

Parameters

aDigest

160 bits in array of unsigned 8-bit octets. Most significant bits first. If you take SHA1 function of openssl library, this is the format the method returns.

Hash() [5/6]

Hash::Hash	(	const char *	aHexString,
		int	aHexStringLen
	)

constructor that takes the hash in ascii string similar that printf("X... produces.

Parameters

aHexString	is the string containing hash value
aHexStringLen	is length of said string. if this param does not have value of 40 then a null hash will be instantiated. Purpose of this parameter is mainly to clearly distinguis this constuctor from the one that has single "unsigned char *" param but expects different length for the string

Hash() [6/6]

Hash::Hash

(

const QSslCertificate &

aSslCert

)

constructor

Parameters

aSslCert

is ssl certificate. Its SHA1 digest is used to initialize value of this hash

Member Function Documentation

calculate()

void Hash::calculate

(

const QByteArray &

aBuf

)

calculates SHA1 hash of data and sets value of this class instance to be the result

distanceFrom()

Hash Hash::distanceFrom

(

const Hash &

aHash

)

Method for calculating distance between 2 hashes.

Obligatory J.R.R. Tolkien quote belongs here.

In this program distance is defined in "number of rings to rule them all" meaning that 1) hash values roll over e.g. distance between Hash(0) and Hash(max value) is 1. Distance between Hash(1) and Hash(max value) is 2. Distance between Hash(1) and Hash(5) is 4. As is to be expected. 2) We may invent many rings to address same objects because from articles (for instance) we can record the article content hash, pgp-key fingerprint of the sender, node used to send, hash of the forum containing the article etc. and in different situations it may be useful to search through different ring. This method distanceFrom tells how far away the number we're seeking for is and notable thing here is that number may roll over when going via path of shortest distance.

Parameters

aHash

is the number from which we calculate distance

Returns

return value is also a hash, that is, a number

fromQVariant()

void Hash::fromQVariant

(

const QVariant &

aQVariantHashValue

)

Sets hash value from QVariant produced by toQVariant() method of this same class.

fromString()

void Hash::fromString

(

const unsigned char *

aBuf

)

Sets hash value from string produced by toString() method of this same class.

operator!=()

bool Hash::operator!=

(

const Hash &

aHashToCompare

)

const

operator+()

Hash Hash::operator+

(

const Hash &

aToBeAdded

)

const

addition operation for integers of 160 bits

operator-()

Hash Hash::operator-

(

const Hash &

aToBeSubstracted

)

const

Man-kinds greatest invention ever follows: bignum operations for small bignums.

Subtraction operator. As our hash if you think of it as a number, is unsigned, this operator will definitely return undefined-kind-of-crap if you try to subtract bigger number from a smaller one. Something you'll get but it can be anything.

Other way around it seems to do something.

operator<()

bool Hash::operator<

(

const Hash &

aHashToCompare

)

const

operator=()

Hash& Hash::operator=

(

const Hash &

aHashToSubstitute

)

substitution too, it might make code more readable

operator==()

bool Hash::operator==

(

const Hash &

aHashToCompare

)

const

Comparison operator enabling us to use sort operations

operator>()

bool Hash::operator>

(

const Hash &

aHashToCompare

)

const

setFromCharArray()

void Hash::setFromCharArray ( const unsigned char  aDigest[KNumberOfIntsInHash *4] )

private

toQVariant()

QVariant Hash::toQVariant

(

)

const

Returns the hash value as a QVariant

toString()

QString Hash::toString

(

)

const

Returns the hash value as a string.

Member Data Documentation

iHash160bits

quint32 Hash::iHash160bits[KNumberOfIntsInHash]

this public array carries the calculated (SHA1) hash. there is 5*32 bits and in db too we're supposed to use 5 columns for storing a hash ; we can still compare and do ordering if we decide that low-order bits go into iHash160bits[0] and the highest into iHash160bits[4].

In 64-bit boxen we could fit the bits into 64-bit integers and have this thing working a bit faster - hopefully this thing will still work fast enough to work also in less-powerful 32-bit architectures for which we don't here want to invent a separate implementation.

KNumberOfIntsInHash

const int Hash::KNumberOfIntsInHash = 5

static

This constant KNumberOfIntsInHash defines size of our hash ; we take this many unsigned ints each 32bits in size so with value 5 w get 5*32=160.

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The documentation for this class was generated from the following file:

• hash.h