size_t + ptrdiff_t
Alex Rønne Petersen
xtzgzorex at gmail.com
Mon Feb 20 04:16:31 PST 2012
On 20-02-2012 09:31, Iain Buclaw 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
>>> 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
>> 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" :~)
IMHO, it should be.
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