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target/ppc/int_helper.c:2806: strange expression ?

target/ppc/int_helper.c:2806:25: warning: ‘*’ in boolean context, suggest ‘&&’ instead [-Wint-in-bool-context]

Source code is

       zone_digit = (i * 2) ? b->u8[BCD_DIG_BYTE(i * 2)] >> 4 : zone_lead;

Which I read as

       zone_digit = (i * 2) ? (b->u8[BCD_DIG_BYTE(i * 2)] >> 4) : zone_lead;

so I think the compiler warning is for the i * 2 lhs of the ?.

I am not sure what to suggest as a bugfix.

On 01/11/2017 10:41 AM, dcb wrote:
> Public bug reported:
> 
> target/ppc/int_helper.c:2806:25: warning: ‘*’ in boolean context,
> suggest ‘&&’ instead [-Wint-in-bool-context]
> 
> Source code is
> 
>        zone_digit = (i * 2) ? b->u8[BCD_DIG_BYTE(i * 2)] >> 4 :
> zone_lead;

Also, looking at BCD_DIG_BYTE():

#if defined(HOST_WORDS_BIGENDIAN)
#define BCD_DIG_BYTE(n) (15 - (n/2))
#else
#define BCD_DIG_BYTE(n) (n/2)
#endif

Oops. n is under-parenthesized, and will cause invalid expansions for
some expressions.  Let's fix that as well.


> so I think the compiler warning is for the i * 2 lhs of the ?.

Yes - the compiler is complaining that 'i * 2' can only be non-zero if
'i' was non-zero (given that the code occurs in a loop for i between 0
and 16), so it is just as easy to write 'i ? ...' instead of the weirder
'(i * 2) ? ...'.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org



> so it is just as easy to write 'i ? ...' instead of the weirder
> '(i * 2) ? ...'.

I suspect it is just possible that the i * 2 expression is a typo
for something else, perhaps i & 2 or i << 2 or i >> 2 or something else.

I don't know the code so I am unable to offer better guidance.
 

Patch has been posted to the mailing list:
https://lists.gnu.org/archive/html/qemu-devel/2017-01/msg02008.html

Fix had been committed here:
http://git.qemu.org/?p=qemu.git;a=commitdiff;h=365206aeb3d0bb72043d