bug#25706: 26.0.50; Slow C file fontification

[Alan Mackenzie]

Hello, Mattias.

On Mon, Nov 30, 2020 at 13:46:30 +0100, Mattias Engdegård wrote:
> >> https://raw.githubusercontent.com/qca/qcamain_open_hal_public/master/hal/ar9300/osprey_reg_map_macro.h

> > I tried reproducing this on a pretty new laptop, and opening the file
> > in question (with your settings) took less than a second with Emacs
> > 28.

> My lappy is less new but not really that slow -- compared to the
> hardware of the original reporter it's a speed demon -- but opening the
> file takes almost 4 s here. More importantly, scrolling through the
> file is painfully slow.

Hah!  I just tried it, all the way through the file, and it took me
3568.429881811142 seconds, i.e. all of an hour bar 32 seconds.

My machine is no way slow, being a first generation AMD Ryzen from 2017.

> Alan, do you have a diagnose?

Other than what I told you last post (lack of braces), not yet, but I'm
going to take the first tenth of the OP's file (which is 4 Mb) for
testing on.

-- 
Alan Mackenzie (Nuremberg, Germany).