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> 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
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