[R] Is there a way to force counters to be treated as "unsigned?"

[jim holtman]

This is handled simply with an AND operator.  You use a mask the size
of the counter:

> require(bitops)
> 3 - 14
[1] -11
> bitAnd(3 - 14, 0xF)
[1] 5
>
>


On Mon, Feb 14, 2011 at 5:45 PM, David Wolfskill <david at catwhisker.org> wrote:
> I am acquiring some sampled data that is time-stamped (with a
> POSIXct).  Some of the data is in the form of "counters" -- that
> is, what is interesting isn't value of a given counter at a given
> time, but the change in the counter from one sample to a later one.
>
> As the counters are only incremented, they would be perceived to be
> monotonically increasing -- ideally.  Unfortunately, the counters can
> "wrap," with the effect being that a later value may appear to be
> smaller than an earlier one.
>
> Other code I've seen (in C) that works with these counters merely casts
> the counters to (unsigned) before calculating the difference, then casts
> the result as (int).  Subject to the constraint that this trick only
> works if the system doing the calculation has the same size "int" as the
> target system, and assumes that negative numbers are represented in
> "twos-complement" form, it works well enough.
>
> [E.g., suppose we are using 4-bit counters, 0 .. 15].  If a counter
> at T0 is (say) 14 and the value of the counter at T1 is (say) 3,
> the usual arithmetic would say that the difference is
>
>        3 - 14 => -11
>
> But if we (instead) calculate
>
>        (int)((unsigned)3 - (unsigned)4) => 5
>
> which works out to be correct.]
>
> Is there a way to do something similar to this in R?
>
> (I suppose that if I know the size of the counters in the original
> environment, I could watch for a negative difference, and if seen, add
> the appropriate power of 2 to the (negative) result.  I would be
> disinclined to consider that "elegant," though. :-})
>
> Peace,
> david
> --
> David H. Wolfskill                              david at catwhisker.org
> Depriving a girl or boy of an opportunity for education is evil.
>
> See http://www.catwhisker.org/~david/publickey.gpg for my public key.
>
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>



-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?