Warnings (was: Subsurface libdivecomputer branch merged with upstream..)

[Lubomir I. Ivanov]

On 16 December 2017 at 14:26, Berthold Stoeger
<bstoeger at mail.tuwien.ac.at> wrote:
> On Freitag, 15. Dezember 2017 15:04:49 CET Lubomir I. Ivanov wrote:
>> On 15 December 2017 at 11:24, Berthold Stoeger
>>
>> <bstoeger at mail.tuwien.ac.at> wrote:
>> > On Mittwoch, 13. Dezember 2017 23:34:32 CET Dirk Hohndel wrote:
>> >> > On Dec 13, 2017, at 11:31 AM, Berthold Stoeger
>> >
>> > Concerning the float warning, I have a patch that turns all float
>> > calculations into double calculations sitting around for a few weeks. I
>> > think float is like short: only to be used in very specific
>> > circumstances. But I'll let the pros decide.
>>
>> i would post the patch as a PR.
>> 'float' is more like 'int' (32bit), so it's good to have a small data
>> type with less precision and not always rely on 'double' or (64bit
>> long).
>
> From a bit-representation point of view, this is correct. From a more abstract
> language point of view I rather get the impression that
>  - short ~ float
>  - int ~ double
>  - long ~ long double
>  - long long ~ unsupported  (is your FP algorithm numerically unstable?)
> The reason being that floating point literals (e.g. 1.0) represent doubles. You
> have to actively force single-precision floating point calculations by writing
> things like "x * 1000.0f".
>

ok, i see what you mean. "double" is the default floating point format in C.

so yes, "float" is like a non-default sized type e.g. "short", yet
one's variable might fit in a "short" and it's perfectly fine to use
the non-default type.
while nowadays we don't have much of a size restrain using the smaller
type, it could be a good indication that we don't actually need the
whole 64bit precision for this variable.
the same way one could use a "char" vs an "int".

on the other hand, if this causes more trouble than benefits, it's
probably best to just convert all the calculations to be with
"doubles", have consistency and silence the -Wall warnings.

lubomir
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