Excessive readFilter->readCell() increase runtime notably when parsing XSLX files

[DennisBirkholz]

This is:

- [x] a bug report

What is the expected behavior?

Parsing with styles enabled or disabled should not have a considerable different parsing time.

What is the current behavior?

A rather large file with ~6000 rows and 10 columns takes about 2 seconds to parse with $reader->setReadDataOnly(false) but takes about 30 seconds with $reader->setReadDataOnly(true).

What are the steps to reproduce?

<?php

require __DIR__ . '/vendor/autoload.php';

// Takes 30 seconds
$reader = \PhpOffice\PhpSpreadsheet\IOFactory::createReaderForFile('large_spreadsheet.xlsx');
$document = $reader->load('large_spreadsheet.xlsx');

// Takes 2 seconds
$reader = \PhpOffice\PhpSpreadsheet\IOFactory::createReaderForFile('large_spreadsheet.xlsx');
$reader->setReadDataOnly(true);
$document = $reader->load('large_spreadsheet.xlsx');

Which versions of PhpSpreadsheet and PHP are affected?

PHP 5.6 and PHPSpreadsheet 1.5.0