bug#22763: 25.1.50; Feature Request -- A faster method to obtain line number at position.

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: 22763@debbugs.gnu.org,  esq@lawlist.com,  monnier@iro.umontreal.ca
> Date: Sun, 07 Feb 2021 22:58:12 +0100
> 
> Never mind -- there are even more optimised versions using SSE2 etc,
> too:
> 
> https://github.com/lattera/glibc/blob/master/sysdeps/x86_64/memchr.S

You need to look at the code emitted by GCC under -O2.  glibc is not
necessarily relevant here.