[fpc-pascal] Floating point question

[Bernd Oppolzer]

In this example below, the performance argument does not count IMO,
because the complete computation can be done at compile time.

That's why IMO in all 3 cases the values on the right side should be 
computed with
maximum precision (of course independent of the left side), and in an 
ideal world
it should be done at compile time. But if not: anyway with max precision.
Tagging the FP constants with FP attributes like single, double and 
extended and
then doing arithmetic on them which leads to MATHEMATICAL results which 
are unexpected
is IMO wrong and would not be accepted in most other programming 
languages or compilers.

This is NOT about variables ... they have attributes and there you can 
explain all sort of
strange behaviour. It's about CONSTANT EXPRESSIONS (which can and should 
be evaluated
at compile time, and the result should be the same, no matter if the 
evaluation is done at
compile time or not).

That said:

if you have arithmetic involving a single variable and a FP constant, say

x + 1440.0

you don't need to handle this as an extended arithmetic IMO, if you 
accept my statement above.
You can treat the 1440.0 as a single constant in this case, if you wish. 
It's all about context ...

Kind regards

Bernd


Am 12.02.2024 um 10:44 schrieb Thomas Kurz via fpc-pascal:
> I wouldn't say so. Or at least, not generally. Why can't the compiler do what the programer intends to do:
>
> var
>    s: single;
>    d: double;
>    e: extended;
>    
> begin
>    s := 8427.0 + 33.0 / 1440.0; // treat all constants all "single"
>    d := 8427.0 + 33.0 / 1440.0; // treat all constants all "double"
>    e := 8427.0 + 33.0 / 1440.0; // treat all constants all "extended"
> end.
>
> Shouldn't this satisfy all the needs? Those caring for precision will work with double precision and don't have to take care for a loss in precision. Those caring for speed can use the single precision type and be sure that no costly conversion to double or extended will take place.
>
>
>
>
> ----- Original Message -----
> From: Jonas Maebe via fpc-pascal <fpc-pascal at lists.freepascal.org>
> To: fpc-pascal at lists.freepascal.org <fpc-pascal at lists.freepascal.org>
> Sent: Sunday, February 11, 2024, 23:29:42
> Subject: [fpc-pascal] Floating point question
>
> On 11/02/2024 23:21, Bernd Oppolzer via fpc-pascal wrote:
>> and this would IMHO be the solution which is the easiest to document and
>> maybe to implement
>> and which would satisfy the users.
> And generate the slowest code possible on most platforms.
>
>
> Jonas
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