On Wed, Mar 6, 2013 at 11:46 AM, N.M. Maclaren wrote:
> On Mar 6 2013, Andrew Pinski wrote:
>>
>>
>> Except GCC implements C's unions as allowing to do type punning as an
>> extension and as far as GCC is concerned that is not going to change
>> any time soon.
>> This is a documented exception to
On Wed, 6 Mar 2013, N.M. Maclaren wrote:
> On Mar 6 2013, Andrew Pinski wrote:
> >
> > Except GCC implements C's unions as allowing to do type punning as an
> > extension and as far as GCC is concerned that is not going to change
> > any time soon.
> > This is a documented exception to the aliasi
On Mar 6 2013, Andrew Pinski wrote:
Except GCC implements C's unions as allowing to do type punning as an
extension and as far as GCC is concerned that is not going to change
any time soon.
This is a documented exception to the aliasing/type punning rules.
The problem is that this is worse tha
Doing a bit more light reading on type-punning wrt unions I came upon
the following (from
http://gcc.gnu.org/onlinedocs/gcc-4.7.1/gcc/Structures-unions-enumerations-and-bit_002dfields-implementation.html#Structures-unions-enumerations-and-bit_002dfields-implementation):
"""
- A member of a union o
On Mar 6 2013, Russell Brennan wrote:
Perhaps I misunderstand how you are defining failure here... what
would be the failure mode? Perhaps if you could provide an example of
the ill-effects that could be seen as a result of this behavior it
would clarify the issue?
Generating bad code. In:
On Wed, Mar 6, 2013 at 10:35 AM, Thomas Koenig wrote:
> Am 04.03.2013 21:34, schrieb N.M. Maclaren:
>
> (quoting documentation about DEC UNIONs for Fortran)
>
>> "However, if you overlay one variable with another smaller variable,
>> that portion of the initial variable is retained that is not ove
Perhaps I misunderstand how you are defining failure here... what
would be the failure mode? Perhaps if you could provide an example of
the ill-effects that could be seen as a result of this behavior it
would clarify the issue?
v/r,
Russell
On Wed, Mar 6, 2013 at 2:15 PM, N.M. Maclaren wrote:
On Mar 6 2013, Russell Brennan wrote:
Ouch.
This seems to be at odds with C's unions, where it is not allowed to do
type punning.
As of gcc 4.4.6, the description above seems to match the C behavior:
Er, no. One simple test does not prove that it will always work; this
sort of thing is mos
>> "However, if you overlay one variable with another smaller variable,
>> that portion of the initial variable is retained that is not overlaid.
>> Depending on the application, the retained portion of an overlaid variable
>> may or may not contain meaningful data and can be utilized at a later
>>
Am 04.03.2013 21:34, schrieb N.M. Maclaren:
(quoting documentation about DEC UNIONs for Fortran)
"However, if you overlay one variable with another smaller variable,
that portion of the initial variable is retained that is not overlaid.
Depending on the application, the retained portion of an o
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