combinations of k bits wp34s  Printable Version + HP Forums (https://archived.hpcalc.org/museumforum) + Forum: HP Museum Forums (https://archived.hpcalc.org/museumforum/forum1.html) + Forum: Old HP Forum Archives (https://archived.hpcalc.org/museumforum/forum2.html) + Thread: combinations of k bits wp34s (/thread248771.html) 
combinations of k bits wp34s  Andrew Nikitin  08242013 The bitwise operations on a calculator is surprisingly fun.
// If input word contains k bits, then the result is next word
I would love to hear stories about using them (bitwise operations) in realistic problems.
Re: combinations of k bits wp34s  Paul Dale  08242013 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  08242013 Is there a reason why the use of L is not supported as in: [<>] XYLX
Cheers Re: combinations of k bits wp34s  Paul Dale  08242013 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.
Re: combinations of k bits wp34s  Walter B  08242013 I don't remember the Lpart 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 opcodes left. Anyway, enough potential to create a big mess on the stack.
d:)
Re: combinations of k bits wp34s  Thomas Klemm  08242013 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 Re: combinations of k bits wp34s  Paul Dale  08242013 This is a bug. Soon to be fixed.
Re: combinations of k bits wp34s  Paul Dale  08242013 The L part was very very early on before the command was dropped.
Re: combinations of k bits wp34s  Didier Lachieze  08252013 Very nice program! Here is a slightly more compact version (3 steps less):
LBL'NXC' 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  08252013 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  08252013 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  09022013 The book you want is Hacker's Delight (2nd Edition) by Henry S. Warren.
It's even available in a Kindle edition for $26.
