Re: Register for text width to be used with \l'..'?

[G. Branden Robinson]

At 2024-11-08T17:20:05+0100, Oliver Corff wrote:
> Again the problem of search terms... OF COURSE line length -> LL is
> what I searched for, alas! I thought in terms of TeX terminology:
> \textwidth which would lead nowhere.

It's not exactly wonderful that the most likely mnemonic for the `\w`
escape sequence is "width", which measures a horizontal distance just
like `\l` and `\n[.l]` do.

This is another regrettable consequence of too swift an acquiescence to
the Ken Thompson minimal hash function principle.  Or of not having
enough memory in one's PDP-11/20.  There's probably enough blame to go
around.

> \n[LL] produces 468000. I tried \l'\n[LL]/10000' but get an "error:
> numeric overflow" message.
> 
> Taking advantage that a register ll is undefined in ms I tried then:
> 
> .nr ll \n[LL]/10000
> \l'\n[ll]'
> 
> That basically does the trick but unfortunately 468000/10000 yields
> 46, not 46.8 in groff (due to groff performing truncating division as
> mentioned in the documentation).
> 
> How can I tweak the arithmetic operation to set the correct value of
> 46.8? Or can I bypass the whole truncating division issue by a smart
> selection of scaling units?

I _might_ have some advice.  But I need to know more.

Why are you dividing by 10,000?  What it is you're trying to achieve?
I feel sure you're not actually trying to draw a rule one ten-thousandth
of the line length in _any_ environment.

Part of the problem might be the `\l` escape sequence trying to impose
its "native" scaling unit of "m" on arguments as soon as it reads them.
Observe:

$ ./build/test-groff -ww -b -ms
.LP
Hello.
.br
\l'\n[LL]/10000u'
troff: backtrace: file '<standard input>':4
troff:<standard input>:4: warning: integer value saturated
.nr a \n[LL]/10000u
.pnr a
a       46      0
\l'(u;\n[LL]/10000)'

No warning arises from the second use of `\l`.

Here's a cleaner exhibit.

$ cat EXPERIMENTS/short-hrule.ms
.LP
Hello.
.br
\l'\n[LL]/10000u'
.br
\l'(u;\n[LL]/10000)'

Regards,
Branden

signature.asc
Description: PGP signature