MongoDB.Bson.IO.JsonScanner.GetNumberToken C# (CSharp) Метод

        private static JsonToken GetNumberToken(JsonBuffer buffer, int firstChar)
        {
            var c = firstChar;

            // leading digit or '-' has already been read
            var start = buffer.Position - 1;
            NumberState state;
            switch (c)
            {
                case '-': state = NumberState.SawLeadingMinus; break;
                case '0': state = NumberState.SawLeadingZero; break;
                default: state = NumberState.SawIntegerDigits; break;
            }
            var type = JsonTokenType.Int64; // assume integer until proved otherwise

            while (true)
            {
                c = buffer.Read();
                switch (state)
                {
                    case NumberState.SawLeadingMinus:
                        switch (c)
                        {
                            case '0':
                                state = NumberState.SawLeadingZero;
                                break;
                            case 'I':
                                state = NumberState.SawMinusI;
                                break;
                            default:
                                if (char.IsDigit((char)c))
                                {
                                    state = NumberState.SawIntegerDigits;
                                }
                                else
                                {
                                    state = NumberState.Invalid;
                                }
                                break;
                        }
                        break;
                    case NumberState.SawLeadingZero:
                        switch (c)
                        {
                            case '.':
                                state = NumberState.SawDecimalPoint;
                                break;
                            case 'e':
                            case 'E':
                                state = NumberState.SawExponentLetter;
                                break;
                            case ',':
                            case '}':
                            case ']':
                            case ')':
                            case -1:
                                state = NumberState.Done;
                                break;
                            default:
                                if (char.IsWhiteSpace((char)c))
                                {
                                    state = NumberState.Done;
                                }
                                else
                                {
                                    state = NumberState.Invalid;
                                }
                                break;
                        }
                        break;
                    case NumberState.SawIntegerDigits:
                        switch (c)
                        {
                            case '.':
                                state = NumberState.SawDecimalPoint;
                                break;
                            case 'e':
                            case 'E':
                                state = NumberState.SawExponentLetter;
                                break;
                            case ',':
                            case '}':
                            case ']':
                            case ')':
                            case -1:
                                state = NumberState.Done;
                                break;
                            default:
                                if (char.IsDigit((char)c))
                                {
                                    state = NumberState.SawIntegerDigits;
                                }
                                else if (char.IsWhiteSpace((char)c))
                                {
                                    state = NumberState.Done;
                                }
                                else
                                {
                                    state = NumberState.Invalid;
                                }
                                break;
                        }
                        break;
                    case NumberState.SawDecimalPoint:
                        type = JsonTokenType.Double;
                        if (char.IsDigit((char)c))
                        {
                            state = NumberState.SawFractionDigits;
                        }
                        else
                        {
                            state = NumberState.Invalid;
                        }
                        break;
                    case NumberState.SawFractionDigits:
                        switch (c)
                        {
                            case 'e':
                            case 'E':
                                state = NumberState.SawExponentLetter;
                                break;
                            case ',':
                            case '}':
                            case ']':
                            case ')':
                            case -1:
                                state = NumberState.Done;
                                break;
                            default:
                                if (char.IsDigit((char)c))
                                {
                                    state = NumberState.SawFractionDigits;
                                }
                                else if (char.IsWhiteSpace((char)c))
                                {
                                    state = NumberState.Done;
                                }
                                else
                                {
                                    state = NumberState.Invalid;
                                }
                                break;
                        }
                        break;
                    case NumberState.SawExponentLetter:
                        type = JsonTokenType.Double;
                        switch (c)
                        {
                            case '+':
                            case '-':
                                state = NumberState.SawExponentSign;
                                break;
                            default:
                                if (char.IsDigit((char)c))
                                {
                                    state = NumberState.SawExponentDigits;
                                }
                                else
                                {
                                    state = NumberState.Invalid;
                                }
                                break;
                        }
                        break;
                    case NumberState.SawExponentSign:
                        if (char.IsDigit((char)c))
                        {
                            state = NumberState.SawExponentDigits;
                        }
                        else
                        {
                            state = NumberState.Invalid;
                        }
                        break;
                    case NumberState.SawExponentDigits:
                        switch (c)
                        {
                            case ',':
                            case '}':
                            case ']':
                            case ')':
                            case -1:
                                state = NumberState.Done;
                                break;
                            default:
                                if (char.IsDigit((char)c))
                                {
                                    state = NumberState.SawExponentDigits;
                                }
                                else if (char.IsWhiteSpace((char)c))
                                {
                                    state = NumberState.Done;
                                }
                                else
                                {
                                    state = NumberState.Invalid;
                                }
                                break;
                        }
                        break;
                    case NumberState.SawMinusI:
                        var sawMinusInfinity = true;
                        var nfinity = new char[] { 'n', 'f', 'i', 'n', 'i', 't', 'y' };
                        for (var i = 0; i < nfinity.Length; i++)
                        {
                            if (c != nfinity[i])
                            {
                                sawMinusInfinity = false;
                                break;
                            }
                            c = buffer.Read();
                        }
                        if (sawMinusInfinity)
                        {
                            type = JsonTokenType.Double;
                            switch (c)
                            {
                                case ',':
                                case '}':
                                case ']':
                                case ')':
                                case -1:
                                    state = NumberState.Done;
                                    break;
                                default:
                                    if (char.IsWhiteSpace((char)c))
                                    {
                                        state = NumberState.Done;
                                    }
                                    else
                                    {
                                        state = NumberState.Invalid;
                                    }
                                    break;
                            }
                        }
                        else
                        {
                            state = NumberState.Invalid;
                        }
                        break;
                }

                switch (state)
                {
                    case NumberState.Done:
                        buffer.UnRead(c);
                        var lexeme = buffer.Substring(start, buffer.Position - start);
                        if (type == JsonTokenType.Double)
                        {
                            var value = XmlConvert.ToDouble(lexeme);
                            return new DoubleJsonToken(lexeme, value);
                        }
                        else
                        {
                            var value = XmlConvert.ToInt64(lexeme);
                            if (value < int.MinValue || value > int.MaxValue)
                            {
                                return new Int64JsonToken(lexeme, value);
                            }
                            else
                            {
                                return new Int32JsonToken(lexeme, (int)value);
                            }
                        }
                    case NumberState.Invalid:
                        throw new Exception(FormatMessage("Invalid JSON number", buffer, start));
                }
            }
        }