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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: .5 against 0.5f
Date: Wed, 28 Oct 2026 06:54:12 -0700
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James Kuyper <jameskuyper@alumni.caltech.edu> writes:

> On 2026-10-27 15:54, Steven G. Kargl wrote:
>> On Tue, 27 Oct 2026 20:15:20 +0100, fir wrote:
>>> Steven G. Kargl pisze:
>>>> On Tue, 27 Oct 2026 18:50:09 +0100, fir wrote:
>>>>> Steven G. Kargl pisze:
>>>>>> On Tue, 27 Oct 2026 11:53:55 +0100, fir wrote:
>>
>> (snip)
>>
>>>>> but the question is:  can using .1 instead of 0.1f make me any
>>>>> harm in code?  like things get slower in runtime?  (assuming i
>>>>> use floats in code not doubles, and the code is a bit time
>>>>> critical like rasterisation goes on floats) why the ai so
>>>>> maniacally puts that f?
>>>>
>>>> Without seeing code and not knowing whether you are concerned
>>>> with the propagation of floating point errors, the only answer
>>>> that one can give for your first two questions is "yes, no,
>>>> maybe".
>>>>
>>>> AI is likely appending the f because you instructed AI to use a
>>>> float type.  Why not ask AI why it appends the f?
>>>
>>> it says:  i add f that the number would be float type instead of
>>> double
>>>
>>> float x=a*1.5;
>>>
>>> it also says in such above case the multiplication would be in
>>> double then converted to float - bout for me its hard to belive
>
> The standard requires that "The usual arithmetic conversions are
> performed on the operands."  (6.5.6p4).  Those conversions are
> described in (6.3.2.8), and require that, in a*1.5, the value of a
> must be converted to a double, and that the multiplication be
> carried out using double arithmetic.  However, no conversion is
> required for a*1.5f, and the multiplication is carried out using
> float arithmetic.  [...]

Maybe.  IIANM the C standard allows floating operations to be
carried out in greater precision than the nominal type of the
expression, and thus a*1.5f might very well be carried out using,
e.g., the same operations as would be used by double.