It is halacha that if one has needs (gadol) during tefilla, and can't hold it, one should go. To keep this very complex halachic discussion simple, let's just assume that we are talking about a situation where:
- It is a case where halacha rules that he indeed must go (e.g. can't wait 72 minutes)
- This is during the strongest case (e.g. Birchat Kriyat Shema or Shmone Eserei if applicable)
My question is, would this person be allowed to read?
[This might be because it will help them not think about holy matters, or because it will speed them up greatly as that is their normal practice, but to keep the question focussed if each is a different halacha, let's just ask about reading because that is what normally helps them with their needs.
The question is kept focussed, but if someone would like to give a comprehensive answer covering gadol and katan, all four/five sections of tefilla brought up under this halacha from pre-pesukei dezimra to shmoneh esrei, as well as discuss different materials for reading, that would be also fantastic.