[R] Integer bit size and the modulus operator

[Ionut Florescu]

Thank you, I didn't notice that. I may have to come up with my own power 
function as well, slower but precise.


jim holtman wrote:
> The other thing that you have to be aware of is that 8^n is not 8 
> multiplied by itself n times.  You are probably using logs to compute 
> this.  Here is a sample of 8^(1:20). The value of 8^2 
> is 64.000000000000004 (not exactly an integer); roundoff errors are 
> apparent in the other values. 
>  
> > 8^(1:20)
>  [1] 8.0000000000000000e+00 6.4000000000000004e+01 
> 5.1200000000000001e+02 4.0960000000000001e+03
>  [5] 3.2768000000000002e+04 2.6214400000000002e+05 
> 2.0971519999999999e+06 1.6777215999999999e+07
>  [9] 1.3421772800000000e+08 1.0737418240000001e+09 
> 8.5899345920000005e+09 6.8719476736000003e+10
> [13] 5.4975581388799997e+11 4.3980465111039999e+12 
> 3.5184372088832001e+13 2.8147497671065600e+14
> [17] 2.2517998136852482e+15 1.8014398509481984e+16 
> 1.4411518807585588e+17 1.1529215046068471e+18
> >
>  
> On 1/30/06, *Ionut Florescu* <ifloresc at stevens.edu 
> <mailto:ifloresc at stevens.edu>> wrote:
>
>     I am a statistician and I come up to an interesting problem in
>     cryptography. I would like to use R since there are some statistical
>     procedures that I need to use.
>     However, I run into a problem when using the modulus operator %%.
>
>     I am using R 2.2.1 and when I calculate modulus for large numbers
>     (that
>     I need with my problem) R gives me warnings. For instance if one
>     does:
>     a=1:40;
>     8^a %% 41
>     one obtains zeros which is not possible since 8 to any power is not a
>     multiple of 41.
>     In addition when working with numbers larger that this and with
>     the mod
>     operator R crashes randomly.
>
>     I believe this is because R stores large integers as real numbers thus
>     there may be lack of accuracy when applying the modulus operator and
>     converting back to integers.
>
>     So my question is this: Is it possible to increase the size of memory
>     used for storing integers? Say from 32 bits to 512 bits (Typical
>     size of
>     integers in cryptography).
>
>     Thank you, any help would be greatly appreciated.
>     Ionut Florescu
>
>     ______________________________________________
>     R-help at stat.math.ethz.ch <mailto:R-help at stat.math.ethz.ch> mailing
>     list
>     https://stat.ethz.ch/mailman/listinfo/r-help
>     PLEASE do read the posting guide!
>     http://www.R-project.org/posting-guide.html
>
>
>
>
> -- 
> Jim Holtman
> Cincinnati, OH
> +1 513 247 0281
>
> What the problem you are trying to solve?