On 11/28/23 20:51, Ivan Krylov wrote:
On Wed, 29 Nov 2023 06:11:23 +1100
Hugh Parsonage <hugh.parson...@gmail.com> wrote:
Rprintf("%lld", (long long) xlength(x));
This is fine. long longs are guaranteed to be at least 64 bits in size
and are signed, just like lengths in R.
Right, this has been my choice for R-devel, at least for now. It still
has downsides. In principle, it is not guaranteed that ptrdiff_t won't
become bigger than long long at some point (but it is extremely unlikely
anyone would run into that in R ever with array indexes). Then, on the
other hand, it may be a waste in some cases, ptrdiff_t is smaller and in
theory the generated code may be faster in some cases (that of course
wouldn't matter for errors or I/O, but maybe in theory it could with
purely string operations).
Rprintf("%td, xlength(x));
Maybe if you cast it to ptrdiff_t first. Otherwise I would expect this
to fail on an (increasingly rare) 32-bit system where R_xlen_t is int
(which is an implementation detail).
In my opinion, ptrdiff_t is just the right type for array lengths if
they have to be signed (which is useful for Fortran interoperability),
so Rprintf("%td", (ptrdiff_t)xlength(x)) would be my preferred option
for now. By definition of ptrdiff_t, you can be sure [*] that there
won't be any vectors on your system longer than PTRDIFF_MAX.
Yes, that is fine, too, with the cast, as long as R_xlen_t is not bigger
than ptrdiff_t. You would have a problem if it ever changed in R. I
don't think it is likely, but, technically, the formal guarantees in the
C standard about for which array indexing ptrdiff_t are somewhat weak,
maybe we might need to change this to support bigger arrays or maybe use
the type R_xlen_t also for something slightly different that needs to be
bigger.
using the string macro found in Mr Kalibera's commit of r85641:
R_PRIdXLEN_T
I think this will be the best solution once we can afford
having our packages depend on R >= 4.4.
Yes, the goal was to allow most C99 way using this macro, so e.g.
Rprintf("my index %" R_PRIdXLEN_T "\n", xlength(x));
(note the space before and after the macro in concatenation to be C++
friendly). This doesn't have the limitations described before, but,
there is a problem with translations. I am still looking into that, but
from what I can tell, gettext doesn't make this possible. A good support
would allow strings described this way and also translated this way,
using the symbolic name of the macro, not the expansion.
But, unless you use gettext/translations, this last option is probably
best. Yet you would have to define the macro if not defined to support R
4.3 and older versions.
Tomas
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