lib: Mark up error names in man pages with .Er

Use the keywords `underflow' and `overflow' in ERANGE summary.

Fix phrasing about `out-of-band' and `sentinel value'.

Either an out-of-band channel, or an in-band sentinel value, could
indicate an error, but an out-of-band sentinel value is a silly
proposition.

Noted by uwe@.

Distinguish altogether invalid syntax from trailing garbage.

EXIT_FAILURE police

Fix infinity detection with isinf(d), not d == HUGE_VAL.

Negative infinity counts as overflow too.

Simplify.

Add example for strtod.

This illustrates all the cases you might be interested in and asserts
theorems in those cases.

Fix description of ERANGE cases again.

Do use the technical terms `overflow' and `underflow', because strtod
sets ERANGE precisely to indicate either of these two conditions, and
they are the right keywords that one might be looking for.

Note that strtod may set ERANGE even if it returns noninfinity and
nonzero -- specifically, if the result is subnormal. This part was
wrong before I `fixed' it and remained wrong after I `fixed' it
earlier this year.

branches: 1.22.2;
Bump date for previous.

strtod yields ERANGE for below-subnormal magnitudes, not underflow.

For a floating-point computation, in the language of IEEE 754,
`underflow' means the output was rounded and is too small to be
represented *normally*.

There are many nonzero floating-point numbers to which the exact
output may have been rounded -- namely subnormals. The condition
under which strtod returns ERANGE for small magnitudes is when the
magnitude of the exact result is so small it is rounded to zero, not
even to a subnormal.

While here, use parallel language about large magnitudes instead of
the (albeit correct) word `overflow', to avoid temptation to treat
`underflow' as the opposite notion with zero instead of infinity.

branches: 1.20.50; 1.20.54;
Add HISTORY: The strtof() and strtold() functions appeared in NetBSD
4.0.

branches: 1.19.10;
Use more macros.

Add strtof(3) and strtold(3); welcome libc 12.137.

Grammar fix.

Due to their "inverse" treatment of the fraction's MSb, update NAN
conversion to construct a quiet NaN on hppa, mips, sh3, and sh5 as well.
Also, remove the portion constructing a ROP on vax; this is not required
by the standard, and in its consequences it is not an appropriate
substitute for a qNaN.

branches: 1.15.6;
Move UCB-licensed code from 4-clause to 3-clause licence.

Patches provided by Joel Baker in PR 22280, verified by myself.

Use
.In header.h
instead of
.Fd #include \*[Lt]header.h\*[Gt]
Much easier to read and write, and supported by groff for ages.
Okayed by ross.

Generate <>& symbolically.

Punctuation fixes.

C99: support INF, INFINITY, NAN and NAN(n-char-sequence-opt) arguments.

Drop unnecessary whitespace and .Pp, sort SEE ALSO, sort sections,
and some minor fixes.

Sprinkle some restrict qualifiers.

branches: 1.8.12;
Add missing .El lines.

add LIBRARY section to man page

update to lite-2

New-style RCS ids.

Use "Er" for argument to -width in the lists in the ERROR sections so that
formatting is consistant.

Remove BUGS section which stated that strtod was unimplemented.

Add RCS indentifiers.

branches: 1.1.1;
Initial revision