From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>

Date: Tue 31 Jan 2006 - 06:27:32 EST

Date: Tue 31 Jan 2006 - 06:27:32 EST

This is a double protection error in real_binary. See the R-devel list for the details. Now fixed.

On Mon, 30 Jan 2006, Ionut Florescu wrote:

> Thank you for the quick reply, I will look into the R packages.

*> For crashing R try this:
**>
**> generator.zp=function(x,p)
**> {a=1:(p-1); b=x^a%%p;
**> if(all(b[1:(p-2)]!=1)&&(b[p-1]==1)){return(x, " Good ")}
**> else{return(x, " No Good, try another integer ")}
**> }
**>
**> This checks if element x is a generator of the group Z_p. If you try
**> this function for p = 41 and x various increasing values eventually it
**> will crash R. That is what I meant by random, at first I started x=2,3
**> so on, when I got to 8, R crashed. Now apparently I can get to 15. When
**> I tried again I got to 20.
**>
**> Ionut Florescu
**>
**>
**> Duncan Murdoch wrote:
**>> On 1/30/2006 11:32 AM, Ionut Florescu 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.
**>>
**>> Could you keep a record of the random crashes, and see if you can make
**>> any of them repeatable? R shouldn't crash. If you can find a
**>> repeatable way to make it crash, then that's a bug that needs to be
**>> fixed. (If it crashes at random it should still be fixed, but it's so
**>> much harder to fix that it's unlikely to happen unless the cases are
**>> ones that look likely to come up in normal situations.)
**>>
**>>
**>>>
**>>> 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).
**>>
**>> No, but there is at least one contributed package that does multiple
**>> precision integer arithmetic. I can't remember the name of it right
**>> now, but Google should be able to find it for you...
**>>
**>> Duncan Murdoch
**>>>
**>>> Thank you, any help would be greatly appreciated.
**>>> Ionut Florescu
**>>>
**>>> ______________________________________________
**>>> R-help@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
**>>
**>>
**>
**> ______________________________________________
**> R-help@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
**>
*

-- Brian D. Ripley, ripley@stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ R-help@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.htmlReceived on Tue Jan 31 07:01:51 2006

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