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

[Eli Zaretskii]

> Date: Wed, 19 May 2021 23:55:27 +0000
> From:  Ben Levy via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> For this section in the line-number-at-pos code:
> 
> /* Check that POSITION is n the visible range of the buffer. */
> if (pos < BEGV || pos > ZV)
>   args_out_of_range (make_int (start), make_int (ZV));
> 
> Shouldn't the lower bound condition be pos < start instead of pos < BEGV?

No, because 'start' is the _byte_ position, whereas 'pos' is the
character position.  So if 'start's value is BEGV_BYTE, the test above
already made sure 'pos' is correct, because it makes the equivalent
text of the character position.  And if 'start' is BEG_BYTE, then
'pos' cannot possibly be less than the beginning of the buffer,
because 'pos >= BEGV_BYTE' is a more strict condition.