AsciiString.cs

public struct AsciiString : IEquatable<AsciiString>
{
    private readonly byte[] _data;

    public AsciiString(byte[] bytes) => _data = bytes;

    public AsciiString(string s) => _data = Encoding.ASCII.GetBytes(s);

    public int Length => _data.Length;

    public static implicit operator ReadOnlySpan<byte>(AsciiString str) => str._data;
    public static implicit operator byte[] (AsciiString str) => str._data;

    public static implicit operator AsciiString(byte[] bytes) => new AsciiString(bytes);
    public static implicit operator AsciiString(string str) => new AsciiString(str);

    public override string ToString() => Encoding.ASCII.GetString(_data);
    public static explicit operator string(AsciiString str) => str.ToString();

    public bool Equals(AsciiString other) => ReferenceEquals(_data, other._data) || SequenceEqual(_data, other._data);
    private bool SequenceEqual(byte[] data1, byte[] data2) => new Span<byte>(data1).SequenceEqual(data2);

    public static bool operator ==(AsciiString a, AsciiString b) => a.Equals(b);
    public static bool operator !=(AsciiString a, AsciiString b) => !a.Equals(b);
    public override bool Equals(object other) => (other is AsciiString) && Equals((AsciiString)other);

    public override int GetHashCode()
    {
        // Copied from x64 version of string.GetLegacyNonRandomizedHashCode()
        // https://github.com/dotnet/coreclr/blob/master/src/mscorlib/src/System/String.Comparison.cs
        var data = _data;
        int hash1 = 5381;
        int hash2 = hash1;
        foreach (int b in data)
        {
            hash1 = ((hash1 << 5) + hash1) ^ b;
        }
        return hash1 + (hash2 * 1566083941);
    }
}