Alex Converse <[email protected]> writes:
> On Sat, Jun 18, 2011 at 3:11 PM, Alex Converse <[email protected]>
> wrote:
>> On Sat, Jun 18, 2011 at 2:03 PM, Alex Converse <[email protected]>
>> wrote:
> [...]
>>>
>>> Because signed integer representation (two's complement; ones's
>>> complement; sign magnitude) is implementation defined this also needs
>>> to to be implementation defined.
>>>
>>> See also:
>>>
>>> 6.5.4
>>>> Some operators (the unary operator ~, and the binary operators <<, >>, &,
>>>> ^, and |,
>>>> collectively described as bitwise operators) are required to have operands
>>>> that have
>>>> integer type. These operators yield values that depend on the internal
>>>> representations of
>>>> integers, and have implementation-defined and undefined aspects for signed
>>>> types.
>>>
>>> Yet we allow all of these
>>>
>>
>> Feel free to propose a better solution.
>
> ping?
A safe method (on 2's complement machines, which we assume) is to use a
union:
static inline int u2s(unsigned x)
{
union { unsigned u; int i; } v = { x };
return v.i;
}
GCC and a few other compilers I tested compile this to nothing, as expected.
--
Måns Rullgård
[email protected]
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