[R] [External] long integer handling

[Richard M. Heiberger]

You need the Rmpfr package.  Your calculation of 2^64 is an ordinary
double precision number with 53 bits of precision.

> library(Rmpfr)
Loading required package: gmp

Attaching package: ‘gmp’

The following objects are masked from ‘package:base’:

    %*%, apply, crossprod, matrix, tcrossprod

C code of R package 'Rmpfr': GMP using 64 bits per limb


Attaching package: ‘Rmpfr’

The following object is masked from ‘package:gmp’:

    outer

The following objects are masked from ‘package:stats’:

    dbinom, dgamma, dnorm, dpois, pnorm

The following objects are masked from ‘package:base’:

    cbind, pmax, pmin, rbind

> class(2)
[1] "numeric"
> class(2^32)
[1] "numeric"
> class(2^64)
[1] "numeric"
> Two <- mpfr(2, precBits=64)
> Two^64
1 'mpfr' number of precision  64   bits
[1] 18446744073709551616
> class(Two^64)
[1] "mpfr"
attr(,"package")
[1] "Rmpfr"
> Two^64 - 1
1 'mpfr' number of precision  64   bits
[1] 18446744073709551615
> getPrec(Two)
[1] 64
> getPrec(2.)
[1] 53
>

On Fri, Nov 13, 2020 at 8:45 PM Yousri Fanous <yousri.fanous using gmail.com> wrote:
>
> I want to calculate 2^64-1 which is
> 18446744073709551615
>
> I set the following options to prevent scientific notation
> options("scipen"=100, "digits"=4)
> > x<-2^64 -1
> > x
> [1] 18446744073709551616
>
> This is not correct. There seem to be still some approximation happening.
> How can I get the correct result?
>
> Yousri
> IBM Canada ltd
> Software developer
>
>         [[alternative HTML version deleted]]
>
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