Re: What is the right way to print a UINTN?

[Andrew Fish <afish@apple.com>]

> On Sep 27, 2016, at 10:27 AM, Kinney, Michael D <michael.d.kinney@intel.com> wrote:
> 
> Andrew,
> 
> Here is the comment in current code that explains some of the why.
> 
>      case 'd':
>        if ((Flags & LONG_TYPE) == 0) {
>          //
>          // 'd', 'u', 'x', and 'X' that are not preceded by 'l' or 'L' are assumed to be type "int".
>          // This assumption is made so the format string definition is compatible with the ANSI C
>          // Specification for formatted strings.  It is recommended that the Base Types be used 
>          // everywhere, but in this one case, compliance with ANSI C is more important, and 
>          // provides an implementation that is compatible with that largest possible set of CPU 
>          // architectures.  This is why the type "int" is used in this one case.
>          //
> 
> If code uses type UINTN or INTN, then the max value that can be used 
> for portable sources is max value for the CPU arch with the smallest
> UINTN width.  For the CPU archs in UEFI/PI specs today, the smallest UINTN
> width is 32-bits.
> 
> Portable sources that use type UINTN must never use values larger than
> 32-bits.  Same for type INTN.  Only use values in signed 32-bit range.
> 
> It is possible for 64-bit specific sources to use type UINTN with values
> larger than 32-bits, but those sources would not be portable and would
> need to be changed to UINT64 to be portable.  Is this the case that are
> really discussing here?
> 

If you have a UINTN that can only represent 32-bits is that not a UINT32 :). 

Thanks,

Andrew Fish

> Thanks,
> 
> Mike
> 
> 
>> -----Original Message-----
>> From: afish@apple.com [mailto:afish@apple.com]
>> Sent: Tuesday, September 27, 2016 9:47 AM
>> To: Eugene Cohen <eugene@hp.com>
>> Cc: Laszlo Ersek <lersek@redhat.com>; Kinney, Michael D <michael.d.kinney@intel.com>;
>> Alexei Fedorov <Alexei.Fedorov@arm.com>; edk2-devel@lists.01.org <edk2-
>> devel@ml01.01.org>
>> Subject: Re: [edk2] What is the right way to print a UINTN?
>> 
>> 
>>> On Sep 27, 2016, at 9:03 AM, Cohen, Eugene <eugene@hp.com> wrote:
>>> 
>>>> Printing UINTN with %x *or* with %d are equally bugs.
>>>> 
>>>> For X64 / AARCH64 / IA64 builds, they are actual bugs (that happen to
>>>> work most of the time).
>>> 
>>> Feel free to file a Bugzilla on the extensive usage of this in edk2 [ducking and
>> running].  :)
>>> 
>>>>> I'm envisioning having to create a slide in the future for UEFI
>>>>> training about the proper use of UINTNs and describing "If you think
>>>>> it may exceed 2^32-1 then upcast to UINT64, otherwise don't worry
>>>>> about it" and it makes me squirm.
>>>> 
>>>> It makes me squirm too. I think the slide should recommend the
>>>> casting
>>>> that I proposed. ;) "There is no conversion specifier dedicated to
>>>> UINTN; the portable way to print it is to cast it to UINT64, then print
>>>> it with %Lx."
>>> 
>>> This is reasonable although I expect to get asked why a lot of the other code doesn't
>> adhere to this recommendation.
>>> 
>> 
>> I think this is a historical artifact. The older version of %x in the EDK (and early
>> edk2) implied UINTN. We hit an issue with C integer math resulting in an int and that
>> seemed to bork some toolchains. That is when things changed from UINTN to int. I guess
>> the cleanup was practical vs. pedantic.
>> 
>> Thanks,
>> 
>> Andrew Fish
>> 
>>> Thanks,
>>> 
>>> Eugene
>>> _______________________________________________
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>>> edk2-devel@lists.01.org
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> 
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