109 lines
3.1 KiB
C#
109 lines
3.1 KiB
C#
using System;
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using System.Numerics;
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using System.Runtime.CompilerServices;
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namespace Spv.Generator
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{
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/// <summary>
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/// Similar to System.HashCode, but without introducing random values.
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/// The same primes and shifts are used.
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/// </summary>
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internal static class DeterministicHashCode
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{
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private const uint Prime1 = 2654435761U;
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private const uint Prime2 = 2246822519U;
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private const uint Prime3 = 3266489917U;
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private const uint Prime4 = 668265263U;
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public static int GetHashCode(string value)
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{
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uint hash = (uint)value.Length + Prime1;
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for (int i = 0; i < value.Length; i++)
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{
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hash += (hash << 7) ^ value[i];
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}
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return (int)MixFinal(hash);
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}
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public static int Combine<T>(ReadOnlySpan<T> values)
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{
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uint hashCode = Prime2;
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hashCode += 4 * (uint)values.Length;
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foreach (T value in values)
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{
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uint hc = (uint)(value?.GetHashCode() ?? 0);
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hashCode = MixStep(hashCode, hc);
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}
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return (int)MixFinal(hashCode);
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}
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public static int Combine<T1, T2>(T1 value1, T2 value2)
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{
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uint hc1 = (uint)(value1?.GetHashCode() ?? 0);
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uint hc2 = (uint)(value2?.GetHashCode() ?? 0);
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uint hash = Prime2;
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hash += 8;
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hash = MixStep(hash, hc1);
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hash = MixStep(hash, hc2);
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return (int)MixFinal(hash);
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}
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public static int Combine<T1, T2, T3>(T1 value1, T2 value2, T3 value3)
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{
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uint hc1 = (uint)(value1?.GetHashCode() ?? 0);
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uint hc2 = (uint)(value2?.GetHashCode() ?? 0);
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uint hc3 = (uint)(value3?.GetHashCode() ?? 0);
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uint hash = Prime2;
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hash += 12;
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hash = MixStep(hash, hc1);
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hash = MixStep(hash, hc2);
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hash = MixStep(hash, hc3);
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return (int)MixFinal(hash);
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}
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public static int Combine<T1, T2, T3, T4>(T1 value1, T2 value2, T3 value3, T4 value4)
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{
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uint hc1 = (uint)(value1?.GetHashCode() ?? 0);
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uint hc2 = (uint)(value2?.GetHashCode() ?? 0);
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uint hc3 = (uint)(value3?.GetHashCode() ?? 0);
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uint hc4 = (uint)(value4?.GetHashCode() ?? 0);
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uint hash = Prime2;
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hash += 16;
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hash = MixStep(hash, hc1);
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hash = MixStep(hash, hc2);
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hash = MixStep(hash, hc3);
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hash = MixStep(hash, hc4);
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return (int)MixFinal(hash);
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}
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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private static uint MixStep(uint hashCode, uint mixValue)
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{
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return BitOperations.RotateLeft(hashCode + mixValue * Prime3, 17) * Prime4;
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}
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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private static uint MixFinal(uint hash)
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{
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hash ^= hash >> 15;
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hash *= Prime2;
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hash ^= hash >> 13;
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hash *= Prime3;
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hash ^= hash >> 16;
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return hash;
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}
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}
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}
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