size_t + ptrdiff_t

[Iain Buclaw]

On 19 February 2012 18:27, Manu <turkeyman at gmail.com> wrote:
> On 19 February 2012 20:07, Timon Gehr <timon.gehr at gmx.ch> wrote:
>>
>> On 02/19/2012 03:59 PM, Manu wrote:
>>>
>>> Okay, so it came up a couple of times, but the questions is, what are we
>>> going to do about it?
>>>
>>> size_t and ptrdiff_t are incomplete, and represent non-complimentary
>>> signed/unsigned halves of the requirement.
>>> There are TWO types needed, register size, and pointer size. Currently,
>>> these are assumed to be the same, which is a false assumption.
>>>
>>> I propose size_t + ssize_t should both exist, and represent the native
>>> integer size. Also something like ptr_t, and ptrdiff_t should also
>>> exist, and represent the size of the pointer.
>>>
>>> Personally, I don't like the _t notation at all. It doesn't fit the rest
>>> of the D types, but it's established, so I don't expect it can change.
>>> But we do need the 2 missing types.
>>>
>>> There is also the problem that there is lots of code written using the
>>> incorrect types. Some time needs to be taken to correct phobos too I
>>> guess.
>>
>>
>> Currently, size_t is defined to be what you call ptr_t, ptrdiff_t is
>> present, and what you call size_t/ssize_t does not exist. Under which
>> circumstances is it important to have a distinct type that denotes the
>> register size? What kind of code requires such a type? It is unportable.
>
>
> It is just as unportable as size_t its self. The reason you need it is to
> improve portability, otherwise people need to create arbitrary version mess,
> which will inevitably be incorrect.
> Anything from calling convention code, structure layout/packing, copying
> memory, basically optimising for 64bits at all... I can imagine static
> branches on the width of that type to select different paths.
> Even just basic efficiency, using 32bit ints on many 64bit machines require
> extra sign-extend opcodes after every single load... total waste of cpu
> time.
>
> Currently, if you're running a 64bit system with 32bit pointers, there is
> absolutely nothing that exists at compile time to tell you you're running a
> 64bit system, or to declare a variable of the machines native type, which
> you're crazy if you say is not important information. What's the point of a
> 64bit machine, if you treat it exactly like a 32bit machine in every aspect?

gdc offers __builtin_machine_(u)int for word size, and
__builtin_pointer_(u)int for pointer size via gcc.builtins module.
Nevermind though, it's not quite a "standard" :~)

-- 
Iain Buclaw

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