First, let's acknowledge that 17 b. seems to work just fine as bitwise and:
17 b./~i.4x 0 0 0 0 0 1 0 1 0 0 2 2 0 1 2 3 However: 17 b./~ 2222222222222222222222222222222222222222x it seems that 17 b. runs into problems with large integers. Thanks, -- Raul On Mon, Feb 3, 2014 at 10:25 AM, Dan Bron <j...@bron.us> wrote: > We can express bitwise < (y and not x) as 20 b. . Is there a way to express > bitwise </\ using b. ? Or, in general, without actually having to explode > an integer into its component bits, and then reassemble them? > > -Dan > > ----- Original Message --------------- > > Subject: Re: [Jprogramming] math requests > From: Raul Miller <rauldmil...@gmail.com> > Date: Mon, 3 Feb 2014 09:44:15 -0500 > To: Programming forum <programm...@jsoftware.com> > > I am going over the messages in this thread slowly, because this > subject requires some thought. But that also means that some of my > responses in this thread will appear slowly. > > Anyways: > > On Thu, Jan 30, 2014 at 1:02 PM, Pascal Jasmin <godspiral2...@yahoo.ca> > wrote: >> http://repl.it/languages/Python is a useful resource for figuring out python >> code. But here is the only part I had trouble understanding: >> >> leftmostbit =: 2&#.@:({. , 0 $~ 2 -~ #)@:(2&#. inv) NB. for some reason >> divides msb by 2. > > Here was the version I came up with: > > leftmostBit=: </\&.#: > > If I compare this to the python code: > > def leftmost_bit( x ): > assert x > 0 > result = 1 > while result <= x: result = 2 * result > return result // 2 > > The python variable 'result' is indeed divided by 2 (// in python is > like <.@% in J), but notice that there's an extra 2 * result in the > loop when result is equal to x. > > Example use: > leftmostBit"0 i.10 > 0 1 2 2 4 4 4 4 8 8 > > And here's the comparable python (leaving out 0 because of the assert): > [leftmost_bit(x) for x in range(1,10)] > [1, 2, 2, 4, 4, 4, 4, 8, 8] > > Anyways, python is a bit quirky (but maybe that is a characteristic of > any computer system), but inspecting the data can work there just as > it can work in J. > > Thanks, > > -- > Raul > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
