Difference between revisions of "LlHash"
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|func_sleep=0.0|func_energy=10.0 | |func_sleep=0.0|func_energy=10.0 | ||
|func=llHash|sort=Hash | |func=llHash|sort=Hash | ||
|func_desc=Returns a 32bit hash for the provided string. | |func_desc=Returns a 32bit hash for the provided string. Returns 0 if the input string is empty. | ||
|return_type=integer | |return_type=integer | ||
|p1_type=string|p1_name=val|p1_desc=String to hash. | |p1_type=string|p1_name=val|p1_desc=String to hash. | ||
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{{LSL DefineRow|[[llOrd]]|Convert a character into an ordinal}} | {{LSL DefineRow|[[llOrd]]|Convert a character into an ordinal}} | ||
{{LSL DefineRow|[[llChar]]|Convert an ordinal into a character}} | {{LSL DefineRow|[[llChar]]|Convert an ordinal into a character}} | ||
|also_articles={{LSL DefineRow||{{wikipedia|List of | |also_articles={{LSL DefineRow||{{wikipedia|List of hash functions}}|}} | ||
{{LSL DefineRow||[https://preshing.com/20110504/hash-collision-probabilities/ Hash Collision Probabilities]|}} | {{LSL DefineRow||[https://preshing.com/20110504/hash-collision-probabilities/ Hash Collision Probabilities]|}} | ||
|notes | |notes | ||
Latest revision as of 09:42, 21 May 2021
| LSL Portal | Functions | Events | Types | Operators | Constants | Flow Control | Script Library | Categorized Library | Tutorials |
Summary
Function: integer llHash( string val );| ? | Function ID |
| 0.0 | Forced Delay |
| 10.0 | Energy |
Returns a 32bit hash for the provided string. Returns 0 if the input string is empty.
Returns an integer
| • string | val | – | String to hash. |
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
| • llOrd | Convert a character into an ordinal | |||
| • llChar | Convert an ordinal into a character |
Articles
| • |  List of hash functions
|
|||
| • | Hash Collision Probabilities |