Pharap/ArduinoHashing

A simple library designed to make it easier to store a hash alongside EEPROM data.

Arduino Hashing

A simple library designed to make it easier to store a hash alongside EEPROM data.

Supported Hash Algorithms

Summation

Simple summation of bytes.

Characteristics

Quality: Poor Hash Type: Any Integer Code Size: Small Speed: Fast

Algorithm

hash = 0

foreach byte in object
	hash = hash + byte

return hash

Knuth Hash

Algorithm provided by Donald Knuth in The Art Of Computer Programming Volume 3, Chapter 6.4.

Characteristics

Quality: Decent Hash Type: 32-bit Unsigned Integer Code Size: Smallish Speed: Unknown

Algorithm

hash = size(object)

foreach byte in object
	hash = ((hash << 5) ^ (hash >> 27)) + byte

return hash

Usage Examples

Saving to EEPROM with Hash

With Hash Type

Fully Qualified

// Save object to EEPROM
Hashing::EEPROM::putWithHash<Hashing::KnuthHash>(address, object)

With Alias

// Create alias for desired hashing function
using Hash = Hashing::KnuthHash;

// Save object to EEPROM
Hashing::EEPROM::putWithHash<Hash>(address, object);

With Function Object

// Create a function object
Hashing::KnuthHash hash;

// Save object to EEPROM
Hashing::EEPROM::putWithHash(address, object, hash)

Reading from EEPROM with Hash

Fully Qualified

// Load object from EEPROM
if(Hashing::EEPROM::getWithHash<Hashing::KnuthHash>(address, object))
{
	// This runs if the hash was valid
}
else
{
	// This runs if the hash was invalid
}

// Load object from EEPROM
if(!Hashing::EEPROM::getWithHash<Hashing::KnuthHash>(address, object))
{
	// This runs if the hash was invalid
}

With Alias

// Create alias for desired hashing function
using Hash = Hashing::KnuthHash;

// Load object from EEPROM
if(Hashing::EEPROM::getWithHash<Hash>(address, object))
{
	// This runs if the hash was valid
}
else
{
	// This runs if the hash was invalid
}

// Create alias for desired hashing function
using Hash = Hashing::KnuthHash;

// Load object from EEPROM
if(!Hashing::EEPROM::getWithHash<Hash>(address, object))
{
	// This runs if the hash was invalid
}

With Function Object

// Create a function object
Hashing::KnuthHash hash;

// Load object from EEPROM
if(Hashing::EEPROM::getWithHash(address, object, hash))
{
	// This runs if the hash was valid
}
else
{
	// This runs if the hash was invalid
}

// Create a function object
Hashing::KnuthHash hash;

// Load object from EEPROM
if(!Hashing::EEPROM::getWithHash(address, object, hash))
{
	// This runs if the hash was invalid
}

Calculating Hashes

Static Member Function

With Alias

// Create alias for desired hashing function
using Hash = Hashing::KnuthHash;

// Compute the hash of an object
auto hash_value = Hash::hash(object);

Without Alias

// Compute the hash of an object
auto hash_value = Hashing::KnuthHash::hash(object);

Function Object

With Alias

// Create alias for desired hashing function
using Hash = Hashing::KnuthHash;

// Create a function object
Hash hash;

// Compute the hash of an object
auto hash_value = hash(object);

Without Alias

// Create a function object
Hashing::KnuthHash hash;

// Compute the hash of an object
auto hash_value = hash(object);