LlHash
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Wiki description
Returns a 32bit hash for the provided string. Returns 0 if the input string is empty.
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;
}See also: functions
See also: articles
Original wiki source
Some wiki templates and tables need their original context. View this article on the Second Life Wiki. Technical wording and examples are retained from the source; historical guidance may differ from current behavior.