public static IEnumerable <Utf8String> Split(this Utf8String src, byte delemeter)
        {
            var start = 0;
            var p     = new Utf8Iterator(src.Bytes);

            while (p.MoveNext())
            {
                if (p.Current == delemeter)
                {
                    if (p.BytePosition - start == 0)
                    {
                        yield return(default(Utf8String));
                    }
                    else
                    {
                        yield return(src.Subbytes(start, p.BytePosition - start));
                    }
                    start = p.BytePosition + 1;
                }
            }

            if (start < p.BytePosition)
            {
                yield return(src.Subbytes(start, p.BytePosition - start));
            }
        }
        public static UInt64 ToUInt64(this Utf8String src)
        {
            UInt64 value = 0;
            var    p     = new Utf8Iterator(src.Bytes);

            while (p.MoveNext())
            {
                var b = p.Current;
                switch (b)
                {
                case 0x30:
                    value = (UInt64)(value * 10);
                    break;

                case 0x31:
                    value = (UInt64)(value * 10 + 1);
                    break;

                case 0x32:
                    value = (UInt64)(value * 10 + 2);
                    break;

                case 0x33:
                    value = (UInt64)(value * 10 + 3);
                    break;

                case 0x34:
                    value = (UInt64)(value * 10 + 4);
                    break;

                case 0x35:
                    value = (UInt64)(value * 10 + 5);
                    break;

                case 0x36:
                    value = (UInt64)(value * 10 + 6);
                    break;

                case 0x37:
                    value = (UInt64)(value * 10 + 7);
                    break;

                case 0x38:
                    value = (UInt64)(value * 10 + 8);
                    break;

                case 0x39:
                    value = (UInt64)(value * 10 + 9);
                    break;

                default: throw new ArgumentOutOfRangeException();
                }
            }

            return(value);
        }
        public static bool TrySearchAscii(this Utf8String src, Byte target, int start, out int pos)
        {
            var p = new Utf8Iterator(src.Bytes, start);

            while (p.MoveNext())
            {
                var b = p.Current;
                if (b <= 0x7F)
                {
                    // ascii
                    if (b == target /*'\"'*/)
                    {
                        // closed
                        pos = p.BytePosition;
                        return(true);
                    }
                    else if (b == '\\')
                    {
                        // escaped
                        switch ((char)p.Second)
                        {
                        case '"':     // fall through
                        case '\\':    // fall through
                        case '/':     // fall through
                        case 'b':     // fall through
                        case 'f':     // fall through
                        case 'n':     // fall through
                        case 'r':     // fall through
                        case 't':     // fall through
                            // skip next
                            p.MoveNext();
                            break;

                        case 'u':     // unicode
                            // skip next 4
                            p.MoveNext();
                            p.MoveNext();
                            p.MoveNext();
                            p.MoveNext();
                            break;

                        default:
                            // unkonw escape
                            throw new ParserException("unknown escape: " + p.Second);
                        }
                    }
                }
            }

            pos = -1;
            return(false);
        }
        public static Int32 ToInt32(this Utf8String src)
        {
            var value   = 0;
            var sign    = 1;
            var p       = new Utf8Iterator(src.Bytes);
            var isFirst = true;

            while (p.MoveNext())
            {
                var b = p.Current;

                if (isFirst)
                {
                    isFirst = false;
                    if (b == '-')
                    {
                        sign = -1;
                        continue;
                    }
                }

                switch (b)
                {
                case 0x30:
                    value = value * 10;
                    break;

                case 0x31:
                    value = value * 10 + 1;
                    break;

                case 0x32:
                    value = value * 10 + 2;
                    break;

                case 0x33:
                    value = value * 10 + 3;
                    break;

                case 0x34:
                    value = value * 10 + 4;
                    break;

                case 0x35:
                    value = value * 10 + 5;
                    break;

                case 0x36:
                    value = value * 10 + 6;
                    break;

                case 0x37:
                    value = value * 10 + 7;
                    break;

                case 0x38:
                    value = value * 10 + 8;
                    break;

                case 0x39:
                    value = value * 10 + 9;
                    break;

                default: throw new ArgumentOutOfRangeException();
                }
            }

            return(value * sign);
        }