size_t + ptrdiff_t

[Iain Buclaw]

On 20 February 2012 11:14, Manu <turkeyman at gmail.com> wrote:
> On 20 February 2012 10:31, Iain Buclaw <ibuclaw at ubuntu.com> wrote:
>>
>> 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" :~)
>
>
> That's beautiful though! Can we alias them, and produce a true D type that
> represents them? :)
>
> My basic issue with these size_t/c_int/core.stdc... stuff, is that it seems
> the intent is to go out of the way to maintain compatibility with C, at the
> expense of sucking C's messy and poorly defined types into D, which is a
> shame. It just results in D having the same crappy archaic typing problems
> as C.
> I appreciate that the C types should exist for interoperability with C (ie,
> their quirks should be preserved for any given compiler/architecture), but
> I'd also like to see strictly defined types in D with no respect to any C
> counterpart, guaranteed by the language to be exactly what they claim to be,
> and not confused depending which compiler you try to use.
>
> These 2 GCC intrinsics would appear to be precisely what I was looking for
> at the start of this thread...


Well, as Walter said, these could be aliased in core.stdc.config.

-- 
Iain Buclaw

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