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Talk:Find first and last set bit of a long integer: Difference between revisions
Talk:Find first and last set bit of a long integer (view source)
Revision as of 22:39, 1 February 2014
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: This kind of things happen to people who love to overload operators. What many fail to realize is that seemingly innocuous expressions <code>a & b == 1</code> could do a lot of harm if one insists on using overloaded operators to force a uniform appearance on tasks that are only superficially similar. --[[User:Ledrug|Ledrug]] 19:44, 9 December 2011 (UTC)
:: Ya, I was beginning to think about that. I personally like polymorphism in operators and functions as a first cut. But I also like to have the ability to step out and get deep into the weeds if something demands it. Problem is that a lot of people seem to be in one camp or the other exclusively. :( --[[User:Dgamey|Dgamey]] 23:12, 9 December 2011 (UTC)
::: Actually, efficient MP engines only keep enough words around to represent the largest <code>1</code> bit needed to represent the number (they also do special tricks to handle negative numbers); they also keep around a count of how many words they are using (well duh!). That means that finding the “largest bit” (assuming positive) is possible in constant time. I don't know whether anyone really bothers with it though; the binary logarithm is not an operation that's needed very often given that the storage size is already known. (Finding the decimal logarithm though, that's tremendously valuable and also horribly expensive.) –[[User:Dkf|Donal Fellows]] 10:18, 12 June 2012 (UTC)
== task requirements ==
Four (or two, depending on you count them) of the task's requirements are:
::::* Define routines (or operators) '''lwb''' and '''upb''' that find the ···
::::* Also: Define the reverse routines (or operators) '''rlwb''' and '''rupb''' that find ···
(The added bold highlighting are mine, as well as the trimming.)
It appears that a vast majority of solutions (examples) haven't implemented the (above) four routines. Are these ''strict'' requirements, or are people (or programmers <big><big>☺</big></big>) allowed to ignore them completely or in part?
As for me, I ignored the first pair of requirements (for the REXX solution) as there didn't seem to be a need for REXX programmers to find the first bit of a number (a number that isn't even stored in binary in the first place), but I could write a pair of REXX subroutines to return a value that satisfies that requirement '''as if''' the number was stored in binary. One thing about REXX is that it can be made to pretend about almost anything. -- [[User:Gerard Schildberger|Gerard Schildberger]] ([[User talk:Gerard Schildberger|talk]]) 22:39, 1 February 2014 (UTC)
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