2D SmallHilbertCurve with 16 bits gives negative numbers for arguments with x > 2^15

Question

2D SmallHilbertCurve with 16 bits gives negative numbers for arguments with x > 2^15

FunMiles opened this issue 7 years ago · 5 comments

Up to nbits=15 all is fine. But for nbits=16 the whole right half plane gives negative coordinates.
I am using the code from maven, but I suspect, looking at the source that this line (72) is to blame:

b |= 1 << bIndex;

It should be
b |= 1L << bIndex;

Answer 1 · 2017-11-14T09:45:45.000Z

Excuse the delay!

This rings a bell inasmuch as I think I've been down that path before (and making that change breaks other stuff), how many dimensions are you using? I might need to revisit the threshold check on forcing the user to use the BigInteger index.

Answer 2 · 2017-11-17T05:24:34.000Z

I've just had a look and your suggested fix looks sensible. All tests pass with that change so I'll need to come up with a failing test to confirm. I'll let you know how I go.

Answer 3 · 2017-11-17T05:39:55.000Z

Good find @FunMiles, thank you very much. I've added a round trip test for the scenario below and it passes with your fix :

bits = 16
dimensions = 2
index = 2^ (bits*dimensions-1) + 1

I'll release the fix now.

Answer 4 · 2017-11-17T05:43:28.000Z

I've released 0.1.3 to Maven Central. Usually visible there within 10 mins or so.

Answer 5 · 2017-11-17T05:47:37.000Z

@FunMiles please try your use case again with 0.1.3 to see if all well, thanks.