[PATCH v4] shell: exchange Dijkstra $(( )) evaluator..

[Kang-Che Sung]

On Wednesday, September 7, 2022, Steffen Nurpmeso <steffen at sdaoden.eu>
wrote:
> Kang-Che Sung wrote in
>  <CADDzAfMesHwLEkMsaw3WcLTQ6fGgr813A0QBE1U793_7xbgh-Q at mail.gmail.com>:
>  |On Wednesday, September 7, 2022, Steffen Nurpmeso <steffen at sdaoden.eu>
>  |wrote:
>  ...
>  |>|> +      if(su_64( i > U32_MAX || ) i >= UZ_MAX / 2 ||
>  ...
>  |>|I have to admit that the amount of macro maze makes it really hard to
>  |>|read ;)
>  |>
>  |> Well it is easier than having lots of #ifdef #else #endif blocks
>  |> in my opinion.  On 32-bit the above would spit out a warning
>  |> (possibly, i have not really looked what compiler/linker flags
>  |> busybox uses) because i>U32_MAX can never be true.  I mean i could
>  ...
>  |Compiler will optimize out always-false expressions without giving any
>  |warning.
>
> Regarding the warning: not if you excess an integer limit.
> If you say if(0){} i go with you.
> Hm.  Well, actually it seems current compilers really do so in
> simplemost test files at least, like
>
>   int main(void){if(10>0xFFFFFFFFFFFFFFFFULL)return 1;return 0;}
>
> But already if it is a bit more complicated there is
>
>   int main(void){
>         unsigned long long int i = 10;
>         if(i>0xFFFFFFFFFFFFFFFFULL)return 1;
>         return 0;}
>
>   t.c:3:6: warning: result of comparison 'unsigned long long' >
18446744073709551615 is always false [-Wtautological-type-limit-compare]
>           if(i>0xFFFFFFFFFFFFFFFFULL)return 1;
>              ~^~~~~~~~~~~~~~~~~~~~~~
>   1 warning generated.
>
> I can assure you that i am surprised, "in earlier times" you would
> have been thrown warnings at.  (gcc 12.2.0 is silent!!!)

Okay, I didn't notice there is such a warning in Clang, but I would prefer
writing this way:

if ( (sizeof(i) > 4 && i > U32_MAX) || i >= UZ_MAX / 2 ...
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