QuotedPairReader.cs

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namespace System.Net.Mail;
 
internal static class QuotedPairReader
{
    internal static bool TryCountQuotedChars(string data, int index, bool permitUnicodeEscaping, out int outIndex, bool throwExceptionIfFail)
    {
        if (index <= 0 || data[index - 1] != '\\')
        {
            outIndex = 0;
            return true;
        }
        int num = CountBackslashes(data, index - 1);
        if (num % 2 == 0)
        {
            outIndex = 0;
            return true;
        }
        if (!permitUnicodeEscaping && data[index] > '\u007f')
        {
            if (throwExceptionIfFail)
            {
                throw new FormatException(System.SR.Format(System.SR.MailHeaderFieldInvalidCharacter, data[index]));
            }
            outIndex = 0;
            return false;
        }
        outIndex = num + 1;
        return true;
    }
 
    private static int CountBackslashes(string data, int index)
    {
        int num = 0;
        do
        {
            num++;
            index--;
        }
        while (index >= 0 && data[index] == '\\');
        return num;
    }
}