[Vm-dev] Sometimes it's too easy, part II

[Igor Stasenko]

+1

with C i was always wondering, why C standard does not provides
an unsigned integer type which size strictly corresponds to size of pointer
type, e.g.
sizeof(some standard uint) == sizeof(void*)
that would solve so many problems and make thing so much easier..

instead they had this:
http://www.gnu.org/software/libc/manual/html_node/Important-Data-Types.html
Data Type: *ptrdiff_t*

This is the signed integer type of the result of subtracting two pointers.
For example, with the declaration char *p1, *p2;, the expression p2 - p1 is
of type ptrdiff_t. This will probably be one of the standard signed integer
types (short int, int or long int), but might be a nonstandard type that
exists only for this purpose.

it is easy to see, that sizeof(ptrdiff_t) should be _at least_ the
sizeof(void*), else it won't be able to cover all possible values when
taking difference between two pointers..
alas, it is signed.. and alas, nothing says that it cannot be _more_ than
size of pointer in memory.. simply because you can always fit values that
take 32 bits into 64-bit value holder..

One could say, that there's size_t that could be used as a unsigned
alternative to ptrdiff_t,
unfortunately, ISO gives no guarantees that its size corresponds to pointer
size.


Btw,look what i found :)
https://gcc.gnu.org/onlinedocs/gcc/Integer-Overflow-Builtins.html#Integer-Overflow-Builtins

that could be useful for implementing small-int arithmetics in plain C..
unfortunately this is extension, and don't shoot for  proposing to use
non-standard C herecy :)


On 26 January 2017 at 21:37, John McIntosh <johnmci at smalltalkconsulting.com>
wrote:

>
> +1
>
> Sent from my iPhone
>
> > On Jan 26, 2017, at 10:58, David T. Lewis <lewis at mail.msen.com> wrote:
> >
> >
> > +1
> >
> > Dave
> >
> >>
> >> Surely since we’re concerned about (ab)use of signed values for
> pointers
> >> to words we ought to define a ‘proper’ sqOop thing and use that
> >> instead of a slightly cleaned up derivative of how the Slang default was
> >> left as ‘int’ twenty years ago?
> >>
> >> Yes, any change means a bunch of work to do but isn’t that always the
> >> price to improve things?
> >>
> >> tim
> >> --
> >> tim Rowledge; tim at rowledge.org; http://www.rowledge.org/tim
> >> Strange OpCodes: LB: connect Line-voltage to BITNET
> >>
> >>
> >>
> >
> >
>
>


-- 
Best regards,
Igor Stasenko.
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