CaseInsensitiveAscii.cs

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using System.Collections;
 
namespace System.Net;
 
internal sealed class CaseInsensitiveAscii : IEqualityComparer, IComparer
{
    internal static readonly CaseInsensitiveAscii StaticInstance = new CaseInsensitiveAscii();
 
    internal static ReadOnlySpan<byte> AsciiToLower => new byte[256]
    {
        0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
        10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
        20, 21, 22, 23, 24, 25, 26, 27, 28, 29,
        30, 31, 32, 33, 34, 35, 36, 37, 38, 39,
        40, 41, 42, 43, 44, 45, 46, 47, 48, 49,
        50, 51, 52, 53, 54, 55, 56, 57, 58, 59,
        60, 61, 62, 63, 64, 97, 98, 99, 100, 101,
        102, 103, 104, 105, 106, 107, 108, 109, 110, 111,
        112, 113, 114, 115, 116, 117, 118, 119, 120, 121,
        122, 91, 92, 93, 94, 95, 96, 97, 98, 99,
        100, 101, 102, 103, 104, 105, 106, 107, 108, 109,
        110, 111, 112, 113, 114, 115, 116, 117, 118, 119,
        120, 121, 122, 123, 124, 125, 126, 127, 128, 129,
        130, 131, 132, 133, 134, 135, 136, 137, 138, 139,
        140, 141, 142, 143, 144, 145, 146, 147, 148, 149,
        150, 151, 152, 153, 154, 155, 156, 157, 158, 159,
        160, 161, 162, 163, 164, 165, 166, 167, 168, 169,
        170, 171, 172, 173, 174, 175, 176, 177, 178, 179,
        180, 181, 182, 183, 184, 185, 186, 187, 188, 189,
        190, 191, 192, 193, 194, 195, 196, 197, 198, 199,
        200, 201, 202, 203, 204, 205, 206, 207, 208, 209,
        210, 211, 212, 213, 214, 215, 216, 217, 218, 219,
        220, 221, 222, 223, 224, 225, 226, 227, 228, 229,
        230, 231, 232, 233, 234, 235, 236, 237, 238, 239,
        240, 241, 242, 243, 244, 245, 246, 247, 248, 249,
        250, 251, 252, 253, 254, 255
    };
 
    public int GetHashCode(object myObject)
    {
        if (!(myObject is string { Length: var length } text))
        {
            return 0;
        }
        if (length == 0)
        {
            return 0;
        }
        return length ^ ((AsciiToLower[(byte)text[0]] << 24) ^ (AsciiToLower[(byte)text[length - 1]] << 16));
    }
 
    public int Compare(object firstObject, object secondObject)
    {
        string text = firstObject as string;
        string text2 = secondObject as string;
        if (text == null)
        {
            if (text2 != null)
            {
                return -1;
            }
            return 0;
        }
        if (text2 == null)
        {
            return 1;
        }
        int num = text.Length - text2.Length;
        int num2 = ((num > 0) ? text2.Length : text.Length);
        for (int i = 0; i < num2; i++)
        {
            int num3 = AsciiToLower[text[i]] - AsciiToLower[text2[i]];
            if (num3 != 0)
            {
                num = num3;
                break;
            }
        }
        return num;
    }
 
    private int FastGetHashCode(string myString)
    {
        int num = myString.Length;
        if (num != 0)
        {
            num ^= (AsciiToLower[(byte)myString[0]] << 24) ^ (AsciiToLower[(byte)myString[num - 1]] << 16);
        }
        return num;
    }
 
    public new bool Equals(object firstObject, object secondObject)
    {
        string text = firstObject as string;
        string text2 = secondObject as string;
        if (text == null)
        {
            return text2 == null;
        }
        if (text2 != null)
        {
            int num = text.Length;
            if (num == text2.Length && FastGetHashCode(text) == FastGetHashCode(text2))
            {
                while (num > 0)
                {
                    num--;
                    if (AsciiToLower[text[num]] != AsciiToLower[text2[num]])
                    {
                        return false;
                    }
                }
                return true;
            }
        }
        return false;
    }
}