On 12/08/2021 04:52, Simon Urbanek wrote:
Dipterix,
this has nothing to do with R. 2^63 is too large to be represented as singed
integer, so the behavior is undefined - to quote from the C99 specs (6.3.1.4):
"If the value of the integral part cannot be represented by the integer type, the
behavior is undefined."
Your subject doesn't match your question as the uint64_t conversion is
well-defined and the same on both platforms, but the conversion to int64_t in
undefined.
As I was writing a reply to say the same thing, a few more comments.
- the example is actually in C++, but also undefined there.
- R is more careful:
> as.integer(2^31)
[1] NA
Warning message:
NAs introduced by coercion to integer range
- there is a sanitizer for this, on platforms including Linux and macOS
(at least with clang,
https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html#supported-platforms).
Cheers,
Simon
On 12/08/2021, at 10:50 AM, Dipterix Wang <dipterix.w...@gmail.com> wrote:
Hi,
I was trying to convert REALSXP to int64_t in C, then found that converting
2^63 is inconsistent across platforms:
On M1 ARM osx, 2^63 (double) bit converting to `int64_t` becomes
9223372036854775807
On x86_64 ubuntu server, 2^63 (double) bit converting to `int64_t` is
-9223372036854775808
I was wondering if this is desired behavior to R?
Here's the code to replicate the results above.
print_bit <- Rcpp::cppFunction(r"(
SEXP print_bit(SEXP obj){
int64_t tmp1 = *REAL0(obj);
printf("%lld ", tmp1);
return(R_NilValue);
}
)")
print_bit(2^63)
Thanks,
- Dipterix
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Brian D. Ripley, rip...@stats.ox.ac.uk
Emeritus Professor of Applied Statistics, University of Oxford
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