RandomizedStringEqualityComparer.cs

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using Internal.Runtime.CompilerServices;
 
namespace System.Collections.Generic;
 
internal abstract class RandomizedStringEqualityComparer : EqualityComparer<string>, IInternalStringEqualityComparer, IEqualityComparer<string>
{
    private struct MarvinSeed
    {
        internal uint p0;
 
        internal uint p1;
    }
 
    private sealed class OrdinalComparer : RandomizedStringEqualityComparer
    {
        internal OrdinalComparer(IEqualityComparer<string> wrappedComparer)
            : base(wrappedComparer)
        {
        }
 
        public override bool Equals(string x, string y)
        {
            return string.Equals(x, y);
        }
 
        public override int GetHashCode(string obj)
        {
            if (obj == null)
            {
                return 0;
            }
            return Marvin.ComputeHash32(ref Unsafe.As<char, byte>(ref obj.GetRawStringData()), (uint)(obj.Length * 2), _seed.p0, _seed.p1);
        }
    }
 
    private sealed class OrdinalIgnoreCaseComparer : RandomizedStringEqualityComparer
    {
        internal OrdinalIgnoreCaseComparer(IEqualityComparer<string> wrappedComparer)
            : base(wrappedComparer)
        {
        }
 
        public override bool Equals(string x, string y)
        {
            return string.EqualsOrdinalIgnoreCase(x, y);
        }
 
        public override int GetHashCode(string obj)
        {
            if (obj == null)
            {
                return 0;
            }
            return Marvin.ComputeHash32OrdinalIgnoreCase(ref obj.GetRawStringData(), obj.Length, _seed.p0, _seed.p1);
        }
    }
 
    private readonly MarvinSeed _seed;
 
    private readonly IEqualityComparer<string> _underlyingComparer;
 
    private unsafe RandomizedStringEqualityComparer(IEqualityComparer<string> underlyingComparer)
    {
        _underlyingComparer = underlyingComparer;
        fixed (MarvinSeed* buffer = &_seed)
        {
            Interop.GetRandomBytes((byte*)buffer, sizeof(MarvinSeed));
        }
    }
 
    internal static RandomizedStringEqualityComparer Create(IEqualityComparer<string> underlyingComparer, bool ignoreCase)
    {
        if (!ignoreCase)
        {
            return new OrdinalComparer(underlyingComparer);
        }
        return new OrdinalIgnoreCaseComparer(underlyingComparer);
    }
 
    public IEqualityComparer<string> GetUnderlyingEqualityComparer()
    {
        return _underlyingComparer;
    }
}