Re: "A diagram of C23 basic types"

On Thu, 26 Jun 2025 21:09:37 GMT
scott@slp53.sl.home (Scott Lurndal) wrote:

Michael S <already5chosen@yahoo.com> writes:

On Thu, 26 Jun 2025 12:31:32 -0700
Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:
 

Lawrence D'Oliveiro <ldo@nz.invalid> writes: 

On Mon, 28 Apr 2025 16:27:38 +0300, Michael S wrote: =20 

IMHO, a need for a common name for IEEE binary128 exists for
quite some time. For IEEE binary256 the real need didn't emerge
yet. But it will emerge in the hopefully near future. =20 

>
A thought: the main advantage of binary types over decimal is
supposed to be speed. Once you get up to larger precisions like
that, the speed advantage becomes less clear, particularly since
hardware support doesn=E2=80=99t seem forthcoming any time soon.
There = 

are 

already variable-precision decimal floating-point libraries
available. And with such calculations, C no longer offers a great
performance advantage over a higher-level language, so you might
as well use the higher-level language.
>
<https://docs.python.org/3/library/decimal.html> =20 

=20
I think there's an implicit assumption that, all else being equal,
decimal is better than binary.  That's true in some contexts,
but not in all.
=20 

>
My implicit assumption is that other sings being equal binary is
better than anything else because it has the lowest variation in ULP
to value ratio.=20
The fact that other things being equal binary fp also tends to be
faster is a nice secondary advantage. For example, it is easy to
imagine hardware that implements S/360 style hex floating point as
fast or a little faster than binary fp, but numerec properties of it
are much worse then sane implementations of binary fp. 

 
But not all decimal floating point implementations used "hex floating
point".
 

IBM's Hex floating point is not decimal. It's hex (base 16).

Burroughs medium systems had BCD floating point - one of the
advantages was that it could exactly represent any floating point
number that could be specified with a 100 digit mantissa and a 2
digit exponent.
 
This was a memory-to-memory architecture, so no floating point
registers to worry about.
 
For financial calculations, a fixed point format (up to 100 digits)
was used.   Using an implicit decimal point, rounding was a matter of
where the implicit decimal point was located in the up to 100 digit
field; so do your calculations in mills and truncate the result field
to the desired precision.
>

For fix point, anything "decimal" is even less useful than in floating
point. I can't find any good explanation for use of "decimal" things in
some early computers except that their designers were, may be, good
engineers, but 2nd rate thinkers.