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C# 32 Bit Implementation of the Zobrist Hashing Algorithm.
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/// <summary> | |
/// https://en.wikipedia.org/wiki/Zobrist_hashing | |
/// Faster then GetHashCode, 6 collisions / 435,000 English words, ~20 Collisions / 400,000 | |
/// random byte patterns. | |
/// </summary> | |
public class ZOB64 : HashAlgorithm | |
{ | |
private ulong[] _table; | |
private ulong hash; | |
private uint hash32; | |
private readonly ulong starthash = 0x391615744853B307; | |
private ZOB32State zhs; | |
public ZOB64() | |
{ | |
hash = starthash; | |
BuildTable(0x7965CBDDD4A9E7AF); | |
} | |
public override int HashSize => 64; | |
public override void Initialize() | |
{ | |
hash = starthash; | |
} | |
protected override void HashCore(byte[] bytes, int ibStart, int cbSize) | |
{ | |
Hash64(bytes, ibStart, cbSize); | |
} | |
private static ulong RotateLeft(ulong value, int count) | |
{ | |
return (value << count) | (value >> (64 - count % 64)); | |
} | |
private unsafe void Hash64(byte[] bytes, int ibStart, int cbSize) | |
{ | |
if (bytes == null) | |
return; | |
if (ibStart >= bytes.Length || cbSize > bytes.Length) | |
return; | |
var i = 1; | |
fixed (byte* pb = bytes) | |
{ | |
var nb = pb + ibStart; | |
while (cbSize >= 1) | |
{ | |
hash ^= RotateLeft(_table[*nb], i++); | |
nb += 1; | |
cbSize -= 1; | |
} | |
} | |
} | |
protected override byte[] HashFinal() | |
{ | |
zhs.hash64 = hash; | |
hash32 = zhs.hi ^ zhs.lo; | |
return hash.GetBytes(); | |
} | |
public void BuildTable(ulong seed) | |
{ | |
var rnd = new CRng1(seed.GetBytes()); | |
var tt = new CHashSet<ulong>(256); | |
_table = new ulong[256]; | |
for (var i = 0; i < 256; i++) | |
{ | |
ulong v; | |
do | |
{ | |
v = rnd.NextULong(); | |
} while (tt.Contains(v)); | |
tt.Add(v); | |
_table[i] = v; | |
} | |
} | |
[StructLayout(LayoutKind.Explicit)] | |
public struct ZOB32State | |
{ | |
[FieldOffset(0)] public ulong hash64; | |
[FieldOffset(0)] public uint lo; | |
[FieldOffset(4)] public uint hi; | |
} | |
} |
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