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.
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
> [[alternative HTML version deleted]]
>
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