combinations of k bits wp34s - Printable Version +- HP Forums (https://archived.hpcalc.org/museumforum) +-- Forum: HP Museum Forums (https://archived.hpcalc.org/museumforum/forum-1.html) +--- Forum: Old HP Forum Archives (https://archived.hpcalc.org/museumforum/forum-2.html) +--- Thread: combinations of k bits wp34s (/thread-248771.html) combinations of k bits wp34s - Andrew Nikitin - 08-24-2013 The bitwise operations on a calculator is surprisingly fun. ```// If input word contains k bits, then the result is next word // containing k bits // Must be in integer (binary?) mode // Start with MASKR k LBL'NXC' RCL X +/- RCL Y AND RCL+ Y RCL L RCL Z RCL Z NOT AND x[<->] Y / SR 01 + RTN ``` I would love to hear stories about using them (bitwise operations) in realistic problems. Re: combinations of k bits wp34s - Paul Dale - 08-24-2013 Nice program, one of the few I've seen so far that use integer mode. You might need to specify the integer sign mode though. Also, the shuffle [<->] command would save a couple of steps I think. - Pauli Re: combinations of k bits wp34s - Thomas Klemm - 08-24-2013 Is there a reason why the use of L is not supported as in: ```[<->] XYLX ``` Cheers Thomas Re: combinations of k bits wp34s - Paul Dale - 08-24-2013 Blame Walter :-) The shuffle command originally accepted five registers and L was permitted in any position, then it was removed and later reinstated in its current form after much discussion and finally the keyboard and display code was added. Allowing the fifth register was an unnecessary complication and the current form fits the opcode layout a lot better. - Pauli Re: combinations of k bits wp34s - Walter B - 08-24-2013 I don't remember the L-part of that discussion ;-) One could ask, however, why that command doesn't allow for shuffling A, B, C, and D as well to generate maximum confusion. Luckily, we don't have sufficient op-codes left. Anyway, enough potential to create a big mess on the stack. d:-) Re: combinations of k bits wp34s - Thomas Klemm - 08-24-2013 It was confusing that the letter L was accepted but instead Y is used. The same happens for A, B, C, D and J, K. This might be a remainder of this discussion? Cheers Thomas Re: combinations of k bits wp34s - Paul Dale - 08-24-2013 This is a bug. Soon to be fixed. - Pauli Re: combinations of k bits wp34s - Paul Dale - 08-24-2013 The L part was very very early on before the command was dropped. - Pauli Re: combinations of k bits wp34s - Didier Lachieze - 08-25-2013 Very nice program! Here is a slightly more compact version (3 steps less): ``` LBL'NXC' FILL +/- AND STO T + STO Z NOT AND RCL/ Z SR 01 + RTN ``` Btw I would be interested by a detailed explanation of how you found this formula. Edited: 25 Aug 2013, 6:22 p.m. Re: combinations of k bits wp34s - Paul Dale - 08-25-2013 I found this pretty quickly, although it doesn't appear to be exactly the same algorithm, it is pretty well explained. - Pauli Re: combinations of k bits wp34s - Andrew Nikitin - 08-25-2013 I once read a book about combinatorial algorithms. From there I learned a trick: x&(-x) leaves the lowest set bit in x. I do not remember the exact details, but it dawned on me that I can use that to implement standard "next combination" generation algorithm (locate rightmost group of consecutive ones, in that group move leftmost bit one step left, move others all the way to the right) entirely in mix of bitwise/arithmetic operations. Turned out, you do not even need too many. Edited: 25 Aug 2013, 10:24 p.m. Re: combinations of k bits wp34s - mjcohen - 09-02-2013 The book you want is Hacker's Delight (2nd Edition) by Henry S. Warren. It's even available in a Kindle edition for \$26.