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From: Thomas Koenig <tkoenig@netcologne.de>
Newsgroups: comp.arch
Subject: Re: Computer architects leaving Intel...
Date: Mon, 16 Sep 2024 07:25:38 -0000 (UTC)
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Tim Rentsch <tr.17687@z991.linuxsc.com> schrieb:
> If the loop variable
> represents degrees C or F, or some other naturally signed measure it
> should be signed (or maybe floating point).

The first one is a bad idea because temperature is a continuous
physical quantity.

The second has bad implications for constructs like

      DO R = 0.0, 1.0, 0.1

where it will depend on details floating point arithmetic if the
number of loop trips is 10 or 11.

You can argue that people can write

      DO R=0.0, 1.05, 0.1

but this construct was error-prone enough that it was deleted
from the Fortran standards.

> What kind of loop it
> is, whether ascending or descending, or what the increment is, etc,
> is secondary;  a more important factor is what sort of value is
> being represented, and in almost all cases that is what should
> determine the type used.

Not for floating point numbers.  For that, you should simply do

      DO I=0,10
        R = I * 0.1

or

      R = 0.0
      DO I=0,10
....
        R = R + 0.1
      END DO

whichever rounding error you prefer.

>> Bringing it back to "architecture" Like Anton Ertl has said, LP64 for
>> C/C++ is a mistake.  It should always have been ILP64, and this nonsense
>> would go away.  Any new architecture should make C ILP64 (looking at you
>> RISC-V, missing yet another opportunity to not make the same mistakes as
>> everyone else).
>
> I believe this view is shortsighted.  The big mistake is developers
> hardcoding types everywhere - especially int, but also long, and
> their unsigned variants.  It's almost never a good idea to hardcode
> a specific width (eg, uint32_t) in a type name used for parameters
> or local variables, but that is by far a very common practice.

Hence Fortran's SELECTED_REAL_KIND and SELECTED_INT_KIND...