PHPOffice / PhpSpreadsheet

        // ----- Copy the block of file headers from the old archive

        $v_size = $v_central_dir['size'];

        while ($v_size != 0) {

            $v_read_size = ($v_size < PCLZIP_READ_BLOCK_SIZE ? $v_size : PCLZIP_READ_BLOCK_SIZE);

            $v_buffer = @fread($v_zip_temp_fd, $v_read_size);

            @fwrite($this->zip_fd, $v_buffer, $v_read_size);

            $v_size -= $v_read_size;

        }

        // ----- Create the Central Dir files header

        for ($i = 0, $v_count = 0; $i < sizeof($v_header_list); ++$i) {

        // ----- Read the file by PCLZIP_READ_BLOCK_SIZE octets blocks

        fseek($v_file_compressed, 10);

        $v_size = $p_header['compressed_size'];

        while ($v_size != 0) {

            $v_read_size = ($v_size < PCLZIP_READ_BLOCK_SIZE ? $v_size : PCLZIP_READ_BLOCK_SIZE);

            $v_buffer = @fread($v_file_compressed, $v_read_size);

            @fwrite($this->zip_fd, $v_buffer, $v_read_size);

            $v_size -= $v_read_size;

        }

        // ----- Close the file

        @fclose($v_file_compressed);

                    // ----- Read the file by PCLZIP_READ_BLOCK_SIZE octets blocks

                    $v_size = $p_entry['compressed_size'];

                    while ($v_size != 0) {

                        $v_read_size = ($v_size < PCLZIP_READ_BLOCK_SIZE ? $v_size : PCLZIP_READ_BLOCK_SIZE);

                        $v_buffer = @fread($this->zip_fd, $v_read_size);

                        /* Try to speed up the code

                        $v_binary_data = pack('a'.$v_read_size, $v_buffer);

                        @fwrite($v_dest_file, $v_binary_data, $v_read_size);

                        */

                        @fwrite($v_dest_file, $v_buffer, $v_read_size);

                        $v_size -= $v_read_size;

                    }

                    // ----- Closing the destination file

                    fclose($v_dest_file);

        // ----- Read the file by PCLZIP_READ_BLOCK_SIZE octets blocks

        $v_size = $p_entry['compressed_size'];

        while ($v_size != 0) {

            $v_read_size = ($v_size < PCLZIP_READ_BLOCK_SIZE ? $v_size : PCLZIP_READ_BLOCK_SIZE);

            $v_buffer = @fread($this->zip_fd, $v_read_size);

            //$v_binary_data = pack('a'.$v_read_size, $v_buffer);

            @fwrite($v_dest_file, $v_buffer, $v_read_size);

            $v_size -= $v_read_size;

        }

        // ----- Write gz file format footer

        $v_binary_data = pack('VV', $p_entry['crc'], $p_entry['size']);

        // ----- Copy the block of file headers from the old archive

        $v_size = $v_central_dir['size'];

        while ($v_size != 0) {

            $v_read_size = ($v_size < PCLZIP_READ_BLOCK_SIZE ? $v_size : PCLZIP_READ_BLOCK_SIZE);

            $v_buffer = @fread($this->zip_fd, $v_read_size);

            @fwrite($v_zip_temp_fd, $v_buffer, $v_read_size);

            $v_size -= $v_read_size;

        }

        // ----- Copy the block of file headers from the archive_to_add

        $v_size = $v_central_dir_to_add['size'];

        // ----- Copy the block of file headers from the archive_to_add

        $v_size = $v_central_dir_to_add['size'];

        while ($v_size != 0) {

            $v_read_size = ($v_size < PCLZIP_READ_BLOCK_SIZE ? $v_size : PCLZIP_READ_BLOCK_SIZE);

            $v_buffer = @fread($p_archive_to_add->zip_fd, $v_read_size);

            @fwrite($v_zip_temp_fd, $v_buffer, $v_read_size);

            $v_size -= $v_read_size;

        }

        // ----- Merge the file comments

        $v_comment = $v_central_dir['comment'] . ' ' . $v_central_dir_to_add['comment'];