Generate A Good Hash Key

P: n/a
I've thought a bit about the issue with hashcodes.
I use hashtables and I suppose that they use the GetHashcode function to
determine the identity of the objects stored. Then I thought that the
GetHashcode would have to return an unique number for every possible object
if I am to use it as key in the hashtable.
I've seen a few implementations on the internet looking like this:
Class C
{
public int propertyA;
public int propertyB;
public override GetHashcode()
{
return propertyA.GetHashcode ^ propertyB.GetHashcode;
}
}
Whould the bitwize OR generate unique hashcodes for objects with all
possible combinations in propertyA and propertyB?
In my current application there are several types of objects that inherit
from a base class that we've written. They are stored in a database and have
a primary key combined from two values in the database. The two values are
object id and version number.Then they have sveral other properties such as
name, createdByUserId, createTimeStamp, updateTimeStamp.
My guess is that I could write a GetHashcode function in the base class
looking like this:
GetHashcode()
{
return (typeof(this)).GetHashcode() ^ this.objectId ^
this.versionNumber();
}
Would this be a good implementation?
Are there any resources which sumarize how to quickly write *good*
GetHashcode() functions?
thanks for the help!
/mortb
'Marc Gravell' <mg******@rm.com> wrote in message
news:%2****************@TK2MSFTNGP11.phx.gbl..
If you mean unique per instance, then the only guaranteed way that I know
of is to have something unique in each instance - a simple static int
counter (along with an instance field) would suffice, where each instance
(in the instance ctor) gets the next value and increments the static
counter (pref. using thread-safe increment).
*however* Assuming your hash would be Int32, you are then limited to 2^32
objects - otherwise then can't be unique! (assuming no complex code to
recycle numbers)
You could implement this either as an abstract base class, but then your
*total* instances (of subtypes of this) would be limited to 2^32.
Is it actually required that they be unique? Although not unknown, this is
not (to my mind) recommended usage for a hash value?
Marc

Well, to determine a hash key for the objects, rather than the unique identity of the objects. Then I thought that the GetHashcode would have to return an unique number for every possible object if I am to use it as key in the hashtable. No; the point of a hash function is to provide a hash key that will.usually. be different.

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  • Key’s hash code is used primarily in conjunction to its equals method, for putting a key in map and then getting it back from map. So, our only focus point is these two methods. So if hash code of key object changes after we have put a key value pair in map, then its almost impossible to fetch the value object back from map.
  • HMAC user-input keys that are longer than the specific hash algorithms blocksize are first shortened. (By running the long keys through the hash. And then using that hash as the actual key.) SHA256 outputs 256 bit hashes. That's 32 bytes. So I suggest you generate 256 bit HMAC secret keys. (Using a cryptographically secure random generator.).

This section shows how to programmatically generate a SAS token for using the Event Hubs REST APIs.

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Note: The following snippet requires OpenSSL and jq.

Using the Shared Access Signature (at HTTP level)

Now that you know how to create Shared Access Signatures for any entities in Service Bus, you are ready to perform an HTTP POST:

That is to say, as the modern complete facelift for extensive Sims series standing, was not permanently going to be a huge amount of pressure on Sims 4 crack in order to do something unique and different. Sims 4 key code. In addition to 4 Sims creator Maxis tried to go back to the basics, focusing on major improvements to Sims themselves, their emotions, movements and interactions.

Basically, we’ve created a new generator that can generate unique, real and free keys for game. World of Warcraft Battle for Azeroth CD Key GeneratorToday we announce World of Warcraft Battle for Azeroth CD Key Generator, a brand new keygen for the most new game from franchise. This tool provides access to both the game installation base and the various modes the instrument installs with the game.World of Warcraft Battle for Azeroth is the seventh set in the, following. Warcraft

Generate Hash Online

Remember, this SAS key works for everything. You can create SAS for a queue, topic, subscription, Event Hub, or relay. If you use per-publisher identity for Event Hubs, you can append /publishers/< publisherid>.

Generate Hash Code

If you give a sender or client a SAS token, they don't have the key directly, and they cannot reverse the hash to obtain it. As such, you have control over what they can access, and for how long. An important thing to remember is that if you change the primary key in the policy, any Shared Access Signatures created from it is invalidated.