mirror of
https://github.com/Ryujinx/Ryujinx.git
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114 lines
3.6 KiB
C#
114 lines
3.6 KiB
C#
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using System;
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using System.Runtime.InteropServices;
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namespace Ryujinx.Graphics.Gpu.Shader.HashTable
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{
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/// <summary>
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/// State of a hash calculation.
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/// </summary>
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struct HashState
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{
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// This is using a slightly modified implementation of FastHash64.
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// Reference: https://github.com/ztanml/fast-hash/blob/master/fasthash.c
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private const ulong M = 0x880355f21e6d1965UL;
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private ulong _hash;
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private int _start;
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/// <summary>
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/// One shot hash calculation for a given data.
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/// </summary>
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/// <param name="data">Data to be hashed</param>
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/// <returns>Hash of the given data</returns>
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public static uint CalcHash(ReadOnlySpan<byte> data)
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{
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HashState state = new HashState();
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state.Initialize();
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state.Continue(data);
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return state.Finalize(data);
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}
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/// <summary>
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/// Initializes the hash state.
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/// </summary>
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public void Initialize()
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{
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_hash = 23;
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}
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/// <summary>
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/// Calculates the hash of the given data.
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/// </summary>
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/// <remarks>
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/// The full data must be passed on <paramref name="data"/>.
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/// If this is not the first time the method is called, then <paramref name="data"/> must start with the data passed on the last call.
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/// If a smaller slice of the data was already hashed before, only the additional data will be hashed.
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/// This can be used for additive hashing of data in chuncks.
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/// </remarks>
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/// <param name="data">Data to be hashed</param>
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public void Continue(ReadOnlySpan<byte> data)
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{
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ulong h = _hash;
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ReadOnlySpan<ulong> dataAsUlong = MemoryMarshal.Cast<byte, ulong>(data.Slice(_start));
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for (int i = 0; i < dataAsUlong.Length; i++)
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{
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ulong value = dataAsUlong[i];
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h ^= Mix(value);
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h *= M;
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}
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_hash = h;
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_start = data.Length & ~7;
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}
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/// <summary>
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/// Performs the hash finalization step, and returns the calculated hash.
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/// </summary>
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/// <remarks>
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/// The full data must be passed on <paramref name="data"/>.
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/// <paramref name="data"/> must start with the data passed on the last call to <see cref="Continue"/>.
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/// No internal state is changed, so one can still continue hashing data with <see cref="Continue"/>
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/// after calling this method.
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/// </remarks>
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/// <param name="data">Data to be hashed</param>
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/// <returns>Hash of all the data hashed with this <see cref="HashState"/></returns>
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public uint Finalize(ReadOnlySpan<byte> data)
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{
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ulong h = _hash;
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int remainder = data.Length & 7;
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if (remainder != 0)
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{
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ulong v = 0;
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for (int i = data.Length - remainder; i < data.Length; i++)
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{
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v |= (ulong)data[i] << ((i - remainder) * 8);
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}
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h ^= Mix(v);
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h *= M;
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}
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h = Mix(h);
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return (uint)(h - (h >> 32));
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}
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/// <summary>
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/// Hash mix function.
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/// </summary>
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/// <param name="h">Hash to mix</param>
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/// <returns>Mixed hash</returns>
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private static ulong Mix(ulong h)
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{
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h ^= h >> 23;
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h *= 0x2127599bf4325c37UL;
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h ^= h >> 47;
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return h;
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}
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}
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}
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