[looping in groff@gnu]

At 2024-08-08T10:07:35+0200, Alejandro Colomar wrote:

On Thu, Aug 08, 2024 at 04:56:36AM GMT, Vincent Lefevre wrote:

quoted

On 2024-08-07 23:19:56 +0200, Alejandro Colomar wrote:

quoted

Hi Vincent,

On Wed, Aug 07, 2024 at 12:56:17PM GMT, Vincent Lefevre wrote:

quoted

The current "If x is 0" is a bit misleading because "is" is not
the equality test, while this condition should apply to both -0
and 0.  Replace this condition by "If x is equal to 0".

How does 'is' differ semantically from 'is equal to' in this case?

"is" designates the value (it is a short for "has the value").
For instance, in the same man page (with the typo fixed):
"If x is NaN" (saying "is equal to" would be incorrect, because
the equality comparison with NaN is always false).

That's why the sqrt(3) man page has

  If x is +0 (-0), +0 (-0) is returned.

and the cbrt(3) man page has

  If x is +0, -0, positive infinity, [...]

"is equal to" corresponds to the usual equality, as written in
a source code. (IEEE 754-2019 actually uses "equals".)

For zero, one can also say "If x is ±0" as in the IEEE 754 standard.
The IEEE 754 standard also uses "zero" in the sense "±0" (but it
never uses "0" in this sense when there may be an ambiguity, knowing
that in practice, "0" has the same meaning as "+0"). In a condition,
when it says something like "x = 0", this means that x is either +0
or -0 because these values compare equal to each other.

Hmmm, I see.  Thanks!  I think "If x is ±0" is the clearest way to say
it.  I'm not sure if that glyph is available everywhere, though.  How
about "If x is 0 or -0"?

I think it's reasonable to assume that it's available.[1]  groff's
terminal output devices will either output it as-is or substitute a
fallback.

$ printf '±\n' | groff -K utf8 -T ascii | cat -s
+-

An argument could be made that this fallback should render "+/-"
instead.

With low-capability devices, there's often no single best answer to how
one should limp along.

In groff, of course, you can ask an output device whether it supports a
given glyph and define a string appropriately--but the first part of
that is not portable to formatters that don't implement groff
extensions, and doing so could rouse the ire of Ingo Schwarze's
mandoc(1).

Regards,
Branden

[1] The ± symbol was in the Seventh Edition Unix troff glyph repertoire
    and is also in ISO 8859-1.  I conclude that it's as portable as
    anything not in US-ASCII gets.