TakoTako/TakoTako.Common/MurmurHash2.cs

using System.Text;

// MIT License
//
// Copyright (c) 2017 Jitbit, 2022 TakoTako contributors
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

namespace TakoTako.Common;

public class MurmurHash2
{
    public static uint Hash(string data)
    {
        return Hash(Encoding.UTF8.GetBytes(data));
    }

    public static uint Hash(byte[] data)
    {
        return Hash(data, 0xc58f1a7a);
    }

    private const uint m = 0x5bd1e995;
    private const int r = 24;

    public static uint Hash(byte[] data, uint seed)
    {
        var length = data.Length;
        if (length == 0)
            return 0;
        var h = seed ^ (uint)length;
        var currentIndex = 0;
        while (length >= 4)
        {
            var k = (uint)(data[currentIndex++] | (data[currentIndex++] << 8) | (data[currentIndex++] << 16) |
                           (data[currentIndex++] << 24));
            k *= m;
            k ^= k >> r;
            k *= m;

            h *= m;
            h ^= k;
            length -= 4;
        }

        switch (length)
        {
            case 3:
                h ^= (ushort)(data[currentIndex++] | (data[currentIndex++] << 8));
                h ^= (uint)(data[currentIndex] << 16);
                h *= m;
                break;
            case 2:
                h ^= (ushort)(data[currentIndex++] | (data[currentIndex] << 8));
                h *= m;
                break;
            case 1:
                h ^= data[currentIndex];
                h *= m;
                break;
        }

        h ^= h >> 13;
        h *= m;
        h ^= h >> 15;

        return h;
    }
}