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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.arch
Subject: Re: Computer architects leaving Intel...
Date: Mon, 16 Sep 2024 19:51:26 -0700
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Thomas Koenig <tkoenig@netcologne.de> writes:

> 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.

That doesn't mean that a quantity representing degrees C or
degrees F in a computer program always has to be a continuous
measure.  Sometimes a signed integer for degrees is what's
needed.  It depends on circumstances.

> 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.

In cases like these I mean R as the loop variable.  The extra
stuff is incidental scaffolding there only to make sure R
takes on all the appropriate values.