With d wired to 2, you can use
msks =: /:~@(> # ]) ~.@,@(+/~)@(0&,)@(i.@:>:@<.&.(2&^.))
msks 64
0 1 2 3 4 5 6 8 9 10 12 16 17 18 20 24 32 33 34 36 40 48
If you need to change d, you can use
msks =: (] #~ (>: +/"1...@#:)) i.
2 msks 64
0 1 2 3 4 5 6 8 9 10 12 16 17 18 20 24 32 33 34 36 40 48
3 msks 32
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 17 18 19 20 21 22 24 25 26 28
Henry Rich
Yuvaraj Athur Raghuvir wrote:
> Hello,
>
> I want to rewrite Java Code[1] to J Code[2] . I want to check with the forum
> members if there is a better way to achieve this.
>
> The issue is that in the setBits loop, the values are set using the
> previously set values. In the process of loop elimination, I found a J form
> and I hand coded the extension to the desired limit. The questions I have
> are:
> 1) For the J pattern I have found, is there a way to use ^: or $: forms?
> 2) Based on the math behind the Java Code, is there a different way to
> achieve this result? I am not able to formulate the problem so I did it the
> debugging way.
>
> Thanks,
> Yuva
>
> Java Code:
> byte[] setBits = new byte[256];
> int d = 2;
> for (int i = 0; i < 256; ++i) setBits[i] = (byte) ((i & 1) + setBits[i
>>> 1]);
> //println(setBits);
> // for every possible key mask...
> masks = new int[0];
> for (int i = 0; i < s; ++i)
> // if d or fewer bits are set...
> if (setBits[(i >> 24) & 0xFF] +
> setBits[(i >> 16) & 0xFF] +
> setBits[(i >> 8) & 0xFF] +
> setBits[ i & 0xFF] <= d)
> // add it to the list of masks.
> masks = append (masks, i);
>
> My J Attempt:
> ls =: (33 b.) NB. bit left shift
> and =: (17 b.) NB. bit and
> or =: (23 b.) NB. bit or
> exor =: (22 b.) NB. bitwise exclusive or
>
>
> v0 =: 13 : ' (2&| i...@# y) + (2&| i...@#y) {~ (_1&ls i...@#y) '
> v1 =: 13 : ' (2&| i...@#y) + ( (-#y) {. (_1&ls i.+:@# y)) { y '
> t2 =. (v0,v...@v0) NB. t2 i.2 gives a string of length 4 on i.2
> t3 =. (t2,v...@t2) NB. 2^3
> t4 =. (t3,v...@t3) NB. 2^4
> t5 =. (t4,v...@t4) NB. 2^5
> t6 =. (t5,v...@t5) NB. 2^6
> t7 =. (t6,v...@t6) NB. 2^7
> t8 =. (t7,v...@t7) NB. 2^8
> sb =. t8 i.2 NB. setBits
> m0 =. (16bff&and)@:(0&ls + _8&ls + _16&ls + _24&ls) sb
> m1 =. <:&2 m0
> msk =: I. m1 NB. masks
>
> t2 i.2
> 0 1 1 2
> t3 i.2
> 0 1 1 2 1 2 2 3
> t4 i.2
> 0 1 1 2 1 2 2 3 1 2 2 3 2 3 3 4
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
>
----------------------------------------------------------------------
For information about J forums see http://www.jsoftware.com/forums.htm
