iTextSharp.text.pdf.PdfReader.ReadXrefSection C# (CSharp) Метод

        protected internal PdfDictionary ReadXrefSection() {
            tokens.NextValidToken();
            if (!tokens.StringValue.Equals("xref"))
                tokens.ThrowError("xref subsection not found");
            int start = 0;
            int end = 0;
            int pos = 0;
            int gen = 0;
            while (true) {
                tokens.NextValidToken();
                if (tokens.StringValue.Equals("trailer"))
                    break;
                if (tokens.TokenType != PRTokeniser.TK_NUMBER)
                    tokens.ThrowError("Object number of the first object in this xref subsection not found");
                start = tokens.IntValue;
                tokens.NextValidToken();
                if (tokens.TokenType != PRTokeniser.TK_NUMBER)
                    tokens.ThrowError("Number of entries in this xref subsection not found");
                end = tokens.IntValue + start;
                if (start == 1) { // fix incorrect start number
                    int back = tokens.FilePointer;
                    tokens.NextValidToken();
                    pos = tokens.IntValue;
                    tokens.NextValidToken();
                    gen = tokens.IntValue;
                    if (pos == 0 && gen == PdfWriter.GENERATION_MAX) {
                        --start;
                        --end;
                    }
                    tokens.Seek(back);
                }
                EnsureXrefSize(end * 2);
                for (int k = start; k < end; ++k) {
                    tokens.NextValidToken();
                    pos = tokens.IntValue;
                    tokens.NextValidToken();
                    gen = tokens.IntValue;
                    tokens.NextValidToken();
                    int p = k * 2;
                    if (tokens.StringValue.Equals("n")) {
                        if (xref[p] == 0 && xref[p + 1] == 0) {
    //                        if (pos == 0)
    //                            tokens.ThrowError("File position 0 cross-reference entry in this xref subsection");
                            xref[p] = pos;
                        }
                    }
                    else if (tokens.StringValue.Equals("f")) {
                        if (xref[p] == 0 && xref[p + 1] == 0)
                            xref[p] = -1;
                    }
                    else
                        tokens.ThrowError("Invalid cross-reference entry in this xref subsection");
                }
            }
            PdfDictionary trailer = (PdfDictionary)ReadPRObject();
            PdfNumber xrefSize = (PdfNumber)trailer.Get(PdfName.SIZE);
            EnsureXrefSize(xrefSize.IntValue * 2);
            PdfObject xrs = trailer.Get(PdfName.XREFSTM);
            if (xrs != null && xrs.IsNumber()) {
                int loc = ((PdfNumber)xrs).IntValue;
                try {
                    ReadXRefStream(loc);
                    newXrefType = true;
                    hybridXref = true;
                }
                catch (IOException e) {
                    xref = null;
                    throw e;
                }
            }
            return trailer;
        }