As long as/long as

Harry Potter and the Chamber of Secrets, by JK Rowling.
The excerpt is the description of a serpent.

"He could see the vast, bloody eye sockets, see the mouth stretching
wide, wide enough to swallow him whole, lined with fangs long as his
sword, thin, glittering, venomous…

I generally use as long as
But I think literary term is quite different.
Please explain if someone knows why this is the case.
I’d be grateful.