hash function...
Author
Hi,
Usually, I use chars or strings as keys to a hash table... what if I want to use integers as keys? How should my hash function be like? A simple mod?
Thanks
edit - sorry, key not hash ;p
Hi.
For integers, you can just use
Hash = Key % TableSize
a more general solution can be to reinterpret whatever data you have as an array of characters, and them sum the ascii values. This is obviously going to be slower than a solution tailored to the data type, but it means you can do things like write a template to wrap a hash table up.
Heres a hashing function i just wrote, lifted from a c++ template
(T is the key type, U is the value type)
[Edited by - fosh on May 23, 2005 8:53:13 AM]
Hi.
For integers, you can just use
Hash = Key % TableSize
a more general solution can be to reinterpret whatever data you have as an array of characters, and them sum the ascii values. This is obviously going to be slower than a solution tailored to the data type, but it means you can do things like write a template to wrap a hash table up.
Heres a hashing function i just wrote, lifted from a c++ template
(T is the key type, U is the value type)
template <class T, class U>int HashTable<T,U>::Hash (T Element){ //Interpret element as an array of characters int ElementSize = sizeof (T) ; unsigned char * TheElement = reinterpret_cast <unsigned char *> (&Element) ; //Summate the ascii values of each character int iTotal = 0 ; for (int i = 0 ; i < ElementSize ; i++) { iTotal += (int) TheElement ; } ; //Convert to hash value int Hash = (iTotal % TableSize) ; return Hash ;} ;[Edited by - fosh on May 23, 2005 8:53:13 AM]
I another similar thread, hplus0603 suggested the PhongHash algorithm:
It will work for any kind of data by just using PhongHash((unsigned char *)&Object, sizeof(Object)) where object can be any variable. I can't say how well it would do though, as I haven't used it myself.
unsigned int PhongHash( unsigned char const * data, size_t size ){ unsigned int hash = 0; while( size-- > 0 ) { hash = 0x63c63cd9*hash + *data + 0x9c39c33d; ++data; } return hash;}It will work for any kind of data by just using PhongHash((unsigned char *)&Object, sizeof(Object)) where object can be any variable. I can't say how well it would do though, as I haven't used it myself.
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