For a long-term horizon, would it help R developers to use a naming
convention?
Perhaps, varName_PROT, or the inverse varName_UNPROT?
Eventually, teach some linter about that?
On Fri, Apr 11, 2025 at 10:40 AM Duncan Murdoch
<murdoch.dun...@gmail.com <mailto:murdoch.dun...@gmail.com>> wrote:
On a tangent from the main topic of this thread: sometimes (especially
to non-experts) it's not obvious whether a variable is protected or not.
I don't think there's any easy way to determine that, but perhaps there
should be. Would it be possible to add a run-time test you could call
in C code (e.g. is_protected(x)) that would do the same search the
garbage collector does in order to determine if a particular pointer is
protected?
This would be an expensive operation, similar in cost to actually doing
a garbage collection. You wouldn't want to do it routinely, but it
would be really helpful in debugging.
Duncan Murdoch
On 2025-04-11 6:05 a.m., Suharto Anggono Suharto Anggono via R-devel
wrote:
> On second thought, I wonder if the caching in my changed
'StringFromLogical' in my previous message is safe. While 'ans' in
the C function 'coerceToString' is protected, its element is also
protected. If the object corresponding to 'ans' is then no longer
protected, is it possible for the cached object 'TrueCh' or
'FalseCh' in 'StringFromLogical' to be garbage collected? If it is,
I think of clearing the cache for each first filling. For example,
by abusing 'warn' argument, the following is added to my changed
'StringFromLogical'.
>
> if (*warn) TrueCh = FalseCh = NULL;
>
> Correspondingly, in 'coerceToString',
>
> warn = i == 0;
>
> is inserted before
>
> SET_STRING_ELT(ans, i, StringFromLogical(LOGICAL_ELT(v, i),
&warn));
>
> for LGLSXP case.
>
> ---------------------
> On Thursday, 10 April 2025 at 10:54:03 pm GMT+7, Martin Maechler
<maech...@stat.math.ethz.ch <mailto:maech...@stat.math.ethz.ch>> wrote:
>
>
>>>>>> Suharto Anggono Suharto Anggono via R-devel
>>>>>> on Thu, 10 Apr 2025 07:53:04 +0000 (UTC) writes:
>
> > Chain of calls of C functions in coerce.c for
as.character(<logical>) in R:
>
> > do_asatomic
> > ascommon
> > coerceVector
> > coerceToString
> > StringFromLogical (for each element)
>
> > The definition of 'StringFromLogical' in coerce.c :
>
> > Chain of calls of C functions in coerce.c for
as.character(<logical>) in R:
> >
> > do_asatomic
> > ascommon
> > coerceVector
> > coerceToString
> > StringFromLogical (for each element)
> >
> > The definition of 'StringFromLogical' in coerce.c :
> >
> > attribute_hidden SEXP StringFromLogical(int x, int *warn)
> > {
> > int w;
> > formatLogical(&x, 1, &w);
> > if (x == NA_LOGICAL) return NA_STRING;
> > else return mkChar(EncodeLogical(x, w));
> > }
> >
> > The definition of 'EncodeLogical' in printutils.c :
> >
> > const char *EncodeLogical(int x, int w)
> > {
> > static char buff[NB];
> > if(x == NA_LOGICAL) snprintf(buff, NB, "%*s", min(w,
(NB-1)), CHAR(R_print.na_string));
> > else if(x) snprintf(buff, NB, "%*s", min(w, (NB-1)),
"TRUE");
> > else snprintf(buff, NB, "%*s", min(w, (NB-1)), "FALSE");
> > buff[NB-1] = '\0';
> > return buff;
> > }
> >
> > > L <- sample(c(TRUE, FALSE), 10^7, replace = TRUE)
> > > system.time(as.character(L))
> > user system elapsed
> > 2.69 0.02 2.73
> > > system.time(c("FALSE", "TRUE")[L+1])
> > user system elapsed
> > 0.15 0.04 0.20
> > > system.time(c("FALSE", "TRUE")[L+1L])
> > user system elapsed
> > 0.08 0.05 0.13
> > > L <- rep(NA, 10^7)
> > > system.time(as.character(L))
> > user system elapsed
> > 0.11 0.00 0.11
> > > system.time(c("FALSE", "TRUE")[L+1])
> > user system elapsed
> > 0.16 0.06 0.22
> > > system.time(c("FALSE", "TRUE")[L+1L])
> > user system elapsed
> > 0.09 0.03 0.12
> >
> > `as.character` of a logical vector that is all NA is fast
enough.
> > It appears that the call to 'formatLogical' inside > the C
function
> > 'StringFromLogical' does not introduce much > slowdown.
>
>
> > I found that using string literal inside the C function
'StringFromLogical', by replacing
> > EncodeLogical(x, w)
> > with
> > x ? "TRUE" : "FALSE"
> > (and the call to 'formatLogical' is not needed anymore),
make it faster.
>
> indeed! ... and we also notice that the 'w' argument is neither
> needed anymore, and that makes sense: At this point when you
> know you have a an R logical value there are only three
> possibilities and no reason ever to warn about the conversion.
>
> > Alternatively,
> or in addition !
>
>
> > "fast path" could be introduced in 'EncodeLogical',
potentially also benefits format() in R.
> > For example, without replacing existing code, the
following fragment could be inserted.
> >
> > if(x == NA_LOGICAL) {if(w == R_print.na_width) return
CHAR(R_print.na_string);}
> > else if(x) {if(w == 4) return "TRUE";}
> > else {if(w == 5) return "FALSE";}
> >
> > However, with either of them, c("FALSE", "TRUE")[L+1L] is
still faster than as.character(L) .
> >
> > Precomputing or caching possible results of the C function
'StringFromLogical' allows as.character(L) to be as fast as
c("FALSE", "TRUE")[L+1L] in R. For example, 'StringFromLogical'
could be changed to
> >
> > attribute_hidden SEXP StringFromLogical(int x, int *warn)
> > {
> > static SEXP TrueCh, FalseCh;
> > if (x == NA_LOGICAL) return NA_STRING;
> > else if (x) return TrueCh ? TrueCh : (TrueCh =
mkChar("TRUE"));
> > else return FalseCh ? FalseCh : (FalseCh =
mkChar("FALSE"));
>
> > }
>
> Indeed, and something along this line (storing the other two
constant strings) was also
> my thought when seeing the
> mkChar(x ? "TRUE" : "FALSE)
> you implicitly proposed above.
>
> I'm looking into applying both speedups;
> thank you very much, Suharto!
>
> Martin
>
>
> --
> Martin Maechler
> ETH Zurich and R Core team
>
> [[alternative HTML version deleted]]
>
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