Word list and hashers to test. More...

Collaboration diagram for ns3::Hash::Example::Dictionary:

Public Member Functions
	Dictionary ()
	Constructor. More...

void	Add (Collider c)
	Add a Collider containing a hash function. More...

void	Add (const std::string phrase)
	Add a string to the dictionary. More...

void	Report () const
	Print the collisions for each Collider. More...

void	ReportExpectedCollisions () const
	Report the expected number of collisions. More...

void	Time ()
	Report the execution time of each hash across the entire Dictionary. More...

void	TimeOne (const int hindex)
	Time and report the execution of one hash across the entire Dictionary. More...

Private Attributes
std::vector< Collider >	m_hashes
	List of hash Colliders. More...

unsigned long	m_nphrases
	Number of strings hashed. More...

std::vector< std::string >	m_words
	List of unique words. More...

Detailed Description

Word list and hashers to test.

Definition at line 271 of file hash-example.cc.

Constructor & Destructor Documentation

ns3::Hash::Example::Dictionary::Dictionary ( )

inline

Constructor.

Definition at line 274 of file hash-example.cc.

References m_words.

Member Function Documentation

void ns3::Hash::Example::Dictionary::Add ( Collider c )

inline

Add a Collider containing a hash function.

Parameters

[in] c The Collider to add.

Definition at line 285 of file hash-example.cc.

References m_hashes.

Referenced by ns3::Hash::Example::DictFiles::ReadInto().

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void ns3::Hash::Example::Dictionary::Add ( const std::string phrase )

inline

Add a string to the dictionary.

Parameters

[in] phrase The string to add.

Definition at line 295 of file hash-example.cc.

References m_hashes, m_nphrases, and m_words.

void ns3::Hash::Example::Dictionary::Report ( ) const

inline

Print the collisions for each Collider.

Definition at line 377 of file hash-example.cc.

References m_hashes, and ReportExpectedCollisions().

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void ns3::Hash::Example::Dictionary::ReportExpectedCollisions ( ) const

inline

Report the expected number of collisions.

See, e.g., http://www.math.dartmouth.edu/archive/m19w03/public_html/Section6-5.pdf

$E(collisions) = n - k + k (1 - 1/k)^n$

where n is the number of entries in the table, and k is the number of buckets.

This form is numerically unstable for low collision rates. Expanding for large $ k $ we get

$\begin{eqnarray*} E(c) &=& \frac{1}{k} \binom{n}{2} - \frac{1}{{{k^2}}} \binom{n}{3} + \frac{1}{{{k^3}}} \binom{n}{4} - \ldots \\ &=& \frac{1}{k} \binom{n}{2} \left[ {1 - \frac{{n - 2}}{{3k}} + \frac{{\left( {n - 2} \right) \left( {n - 3} \right)}}{{12{k^2}}} - \ldots } \right] \\ &=& \frac{1}{k} \binom{n}{2} \left\{ {1 - \frac{{n - 2}}{{3k}} \left[ {1 + \frac{{n - 3}}{{4k}} - \ldots } \right]} \right\} \end{eqnarray*}$