Re^2: Newbie question


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Re^2: Newbie question

by oldB51 (Sexton)

on Aug 24, 2022 at 07:23 UTC ( [id://11146355]=note: print w/replies, xml )

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in reply to Re: Newbie question
in thread Newbie question

Thank you AnomalousMonk. I think the point you are making is that when summing digits: if we consider integers of the form abc say then -abc will always sum to 2a less than abc. 2a is always even so abc and -abc must always both be odd or both even. Hence no need to worry about absolute values for this purpose. Please forgive me if I have not expressed this in a correct formal way - it is over 40 years since I did any mathematics. Your point is excellent.

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Re^3: Newbie question
by AnomalousMonk (Archbishop) on Aug 24, 2022 at 16:10 UTC

... no need to worry about absolute values for this purpose.

Yes, that's the point I was getting at. I also wanted to hint that you don't even need to be concerned with the numbers themselves, but only with the least-significant bit of each number (in 2s'-complement binary representation). The LS bit determines the odd/even status of a number, so adding up all these bits mod 2 (i.e., masking with 1) gives the answer.