bug#44284: 27.1; with some Unicode font, scrolling upward with the mouse wheel actually scrolls downward when the cursor needs repositioning

[Eli Zaretskii]

> Date: Sun, 1 Nov 2020 18:32:40 +0100
> From: Vincent Lefevre <vincent@vinc17.net>
> Cc: 44284@debbugs.gnu.org
> 
> When the cache is filled with
> 
>       cache->ascent = ceil (- extents.y_bearing);
> 
> extents.y_bearing (whose type is double) is equal to:
> 
> Font size 13: -0x1.6000000000001p+3 ≈ -11.000000000000002
> Font size 14: -0x1.8p+3 = -12
> 
> With ceil(), 11.000000000000002 rounds to 12, while the expected value
> is 11. A rounding issue, as I guessed at
> 
>   https://debbugs.gnu.org/cgi/bugreport.cgi?bug=44284#29

Thanks.  Do you have a suggestion for a fix?