The fastest .NET hash generator.

Question

I am implementing a custom GetHashCode for the System.Drawing.Point class in C #. My method currently does not fulfill the following requirement:

var hashA = MyGetHashCode(new Point(1, 0));
var hashB = MyGetHashCode(new Point(0, 1));
var hashC = MyGetHashCode(new Point(0, 0));
var hashD = MyGetHashCode(new Point(1, 1));
Assert.AreNotEqual(hashA ^ hashB, hashC ^ hashD);

To pass this test, I am sure that with the new SHA256Managed (), ComputeHash (currentHash) will work. But is there any other hash algorithm? I know that SHA256 is about security, and I don't need it.

Answer 1

Simple hash? how about something like:

 (17 * point.X) + (23 * point.Y);

Or for a more obvious entropy:

int hash = -1047578147;
hash = (hash * -1521134295) + point.X;
hash = (hash * -1521134295) + point.Y;

(digits from C # anonymous type code)

Answer 2

• Why are you doing it? Does it System.Drawing.Pointalready have a thin hash function?

• , , ? - .

• , .

Answer 3

, , , . :
http://msdn.microsoft.com/en-us/library/system.object.gethashcode.aspx

GetHashCode . ,.NET Framework GetHashCode it .NET. . , .

Answer 4

:

Answer 5

( delphi, shoudl )

function ElfHash(id : string; tableSize : integer) : integer;
var
  i : integer;
  h,x : longint;
begin
  h := 0;
  // Obtener el valor numérico
  for i := 1 to Length(id) do
  begin
    h := (h shl 4) + Ord(id[i]);

    x := h and $F0000000;
    if x <;>; 0 then
       h = h xor (x shr 24) xor x;
  end;
  // Ajustar al tamaño de la tabla
  result := h mod tableSize;
end;

Answer 6

, , Zobrist.

http://en.wikipedia.org/wiki/Zobrist_hashing

, .

Answer 7

, 0 N, hashcode = X+Y*N; . , , . , , N 2. .

I have used this strategy for an excellent effect in the past, but I admit that it has some real (but obvious) limitations. The biggest one is what happens when N is large enough so that N ^ 2 does not fit into your hash value (i.e. painful collisions.