code question

[Ian Lance Taylor]

On Thu, Sep 27, 2012 at 7:18 AM, JD <jd1008@gmail.com> wrote:
>
> On 09/26/2012 11:17 PM, Ian Lance Taylor wrote:
>>
>> On Wed, Sep 26, 2012 at 10:07 PM, JD <jd1008@gmail.com> wrote:
>>>
>>> On 09/26/2012 10:46 PM, Ian Lance Taylor wrote:
>>>>
>>>> On Wed, Sep 26, 2012 at 6:18 PM, JD <jd1008@gmail.com> wrote:
>>>>>
>>>>> I came across this patch which could be cause of a bug.
>>>>>
>>>>> What are possible side effects of this
>>>>> code segment if compiled under various
>>>>> non-gnu C compilers, and GCC compilers?
>>>>>
>>>>>> +inline uint32_t NS_MIN(uint32_t a, uint64_t b)
>>>>>> +{
>>>>>> +  return b < a ? b : a;
>>>>>> +}
>>>>>
>>>>> Nit: Please cast the 64-bit variable to 32-bit in case compilers start
>>>>> warning about it.
>>>>>
>>>>>> +      *pProgress = NS_MIN<PRUint64>(totalBytes - bytesLeft,
>>>>>> PR_UINT32_MAX);
>>>>
>>>> It's very hard to determine the behaviour of an incomplete program.
>>>> It's even harder when you show us two incompatible code fragments.
>>>> You are defining a non-template function NS_MIN and calling a template
>>>> function NS_MIN.  I would expect a compiler error.  I don't know what
>>>> you are seeing.
>>>>
>>>> The basic groundrules for this kind of question are: tell us precisely
>>>> what you did, tell us precisely what happened, and tell us what you
>>>> expected to happen instead.
>>>>
>>>> Ian
>>>>
>>> I was hoping to see what programmers would have to
>>> say about comparing unsigned 32 bit with unsigned 64 bit
>>> in the line
>>>
>>>
>>> return b < a ? b : a;
>>>
>>> does the C compiler first promote the 32  bit  to 64 bit before the
>>> comparison
>>> or vice versa - the 64 bit demoted to 32 bit before comparison.
>>
>>
>> Please reply to the mailing list, not just to me.  Thanks.
>>
>>
>> if you compare an unsigned 32-bit value to an unsigned 64-bit value,
>> the unsigned 32-bit value will be zero-extended to 64-bits, and the
>> values will be compared as unsigned 64-bit values.
>>
>> Ian
>>
> Thanx - but,re responding - Thunderbird did that when I clicked on Reply.
> It replied to you instead of mailing list. Sorry about that. Will watch for
> it
> next time.
> Re: zero extending the 32 bit value by the compiler before comparison.
> Is it zero extended on left or on right?

On the left.

Note that this is not actually a question about GCC.  It is a question
about the C language.

Ian