llHash

Category: Cryptography

function

Function syntax

integer llHash(

string val// String to hash.

);

Returns: integer
Energy: 10

Returns an integer representing the 32-bit hash value of the string val (returns 0 if the string is empty).

Returns a 32bit hash for the provided string. Returns 0 if the input string is empty.

integer result = llHash("");

Specification

The SDBM algorithm provides a good general purpose hash function with a fairly even distribution across the 32 bit space in the general case.

The characters fed into the hash function are 32bit wide.

U32 SDBMHash(const std::wstring &val)
{
    U32 hash(0);

    for(const wchar_t &c: val)
    {
        hash = c + (hash << 6) + (hash << 16) - hash;
    }
    return hash;
}

In LSL:

integer llSDBMHash(string value)
{
    integer hash = 0;
    integer index = 0;
    for (index = 0; index < llStringLength(value); ++index)
    {
        hash = llOrd(value, index) + (hash << 6) + (hash << 16) - hash;
    }

    return hash;
}

Caveats

This hash value is not cryptographically secure and should not be used as part of any security protocol.

SDBM provides a good distribution of hash values across its range, however with only

32 bits the chance of a collision is unacceptably high.(with 1000 entries, the odds for a collision are about 1 in 10000.)

Examples

Given the combination of the object name and the owner’s key generate a unique number. This number could be used for things

like selecting a chat channel that has a low probability of colliding with another object.

integer pickIDForObject()
{
    /* Generate an arbitrary integer ID for the combination of the
     * object name and the ower's key.  This value could be used
     * for selecting a chat/listen channel.
     */
    string obj_name = llGetObjectName();
    key obj_owner = llGetOwner();

    integer hash = llHash(obj_name + (string)obj_owner);

    return hash;
}

llHash

Specification

Caveats

Examples

See also

Functions

Articles