* Signed-unsigned comparison question
@ 2019-03-07 23:40 Zoltan Kocsi
2019-03-07 23:53 ` Zoltan Kocsi
0 siblings, 1 reply; 2+ messages in thread
From: Zoltan Kocsi @ 2019-03-07 23:40 UTC (permalink / raw)
To: gcc
Gcc 8.2.0 (arm-none-eabi) throws a warning on the following construct:
uint32_t a;
uint16_t b;
if ( a > b ) ...
compaining that a signed integer is compared against an unsigned.
Of course, it is correct, as 'b' was promoted to int.
But shouldn't it be smart enough to know that (int) b is restricted to
the range of [0,65535] which it can safely compare against the range of
[0,0xffffffffu]?
Thanks,
Zoltan
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Signed-unsigned comparison question
2019-03-07 23:40 Signed-unsigned comparison question Zoltan Kocsi
@ 2019-03-07 23:53 ` Zoltan Kocsi
0 siblings, 0 replies; 2+ messages in thread
From: Zoltan Kocsi @ 2019-03-07 23:53 UTC (permalink / raw)
To: gcc
Correction:
The construct gcc complains about is not
if ( a < b ) ...
but
if ( a < b - ( b >> 2 ) ) ...
but still the same applies. The RHS of the > operator can never be
negative or have an overflow on 32 bits.
On Fri, 8 Mar 2019 10:40:06 +1100
Zoltan Kocsi <zoltan@bendor.com.au> wrote:
> Gcc 8.2.0 (arm-none-eabi) throws a warning on the following construct:
>
> uint32_t a;
> uint16_t b;
>
> if ( a > b ) ...
>
> compaining that a signed integer is compared against an unsigned.
> Of course, it is correct, as 'b' was promoted to int.
>
> But shouldn't it be smart enough to know that (int) b is restricted to
> the range of [0,65535] which it can safely compare against the range
> of [0,0xffffffffu]?
>
> Thanks,
>
> Zoltan
^ permalink raw reply [flat|nested] 2+ messages in thread
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