Re: [PATCH] ls: add --sort=width (-W) option to sort by filename width

[Carl Edquist]

On Sat, 10 Apr 2021, P@draigBrady.com wrote:

> I've attached two patches ...
>
> The first adjusts your patch to:
>   ...
>   Expand in texinfo that --sort=width is most useful with -C (the default)

FWIW i run 'ls -lW' often enough also, to refresh myself of the details of 
the files with pesky long names that i might want to do something about.

> The second is a performance improvement,
> as we're now calling quote_name_width a lot more.

Cool!

Yeah in theory i felt bad about the performance overhead, but in practice 
it took a directory with on the order of 10k entries before the runtime of 
'ls -W >/dev/null' would even be visible to the human eye, after hitting 
the enter key.  Which seemed reasonable for most interactive purposes.

And if you are actually writing to the terminal in such cases, the runtime 
is completely dominated by the terminal rendering.

Still, the version with caching is definitely more efficient, so that is 
great.


PS if you are willing to cheat a bit and treat the f->width member as 
"mutable" (modifying it even when f is pointer to const), you could 
simplify things a bit if you just store the value from quote_name_width() 
in fileinfo_name_width().  Something like [1].

Then you can completely drop the new update_current_files_info function, 
and get the caching automatically whenever width needs to be calculated.

(And i see your point about avoiding saving the value in the case of 
'--format=commas', to maximize hardware caching - but as far as i could 
tell, even with 100k directory entries, there was no measurable cpu 
performance hit with --format=commas between the current version with 
update_current_files_info(), and the version that always saves f->width 
when it is calculated.)


Anyway, fun times!  :)

Carl


[1]
--- a/src/ls.c
+++ b/src/ls.c
@@ -3892,9 +3892,12 @@ cmp_extension (struct fileinfo const *a, struct fileinfo 
const *b,
 static inline size_t
 fileinfo_name_width (struct fileinfo const *f)
 {
-  return f->width
-         ? f->width
-         : quote_name_width (f->name, filename_quoting_options, f->quoted);
+  if (!f->width)
+    {
+      ((struct fileinfo *) f)->width =
+        quote_name_width (f->name, filename_quoting_options, f->quoted);
+    }
+  return f->width;
 }

 static inline int