BitSet shift left - skip zero words #50
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julienrf
reviewed
Sep 26, 2019
| var significantWordCount = bs.nwords | ||
| while (significantWordCount > 0 && bs.word(significantWordCount - 1) == 0) { | ||
| significantWordCount -= 1 | ||
| } |
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Would it be possible to compute the amount to subtract from significantWordCount in O(1) time?
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I really doubt this. AFAIK BitSet implementation does not keep track of its most significant word/bit. Or maybe you have some idea?
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No, I haven’t thought about how to do this. This was just a question that popped up as I was quickly reading the diff.
julienrf
approved these changes
Sep 26, 2019
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I've realized that Scala
BitSets might have (and usually they do have) some zero words above the highest set bit, which I guess contradicts the statement in the documentation:My initial implementation of
<<kept those zero words and pushed them to the left. As a result, there was an edge case with large BitSets, where those zero words would not fit in the size limit.For example,
BitSet(Int.MaxValue - 64) << 64would throw anIllegalArgumentExceptionwhile it should result inBitSet(Int.MaxValue).I am submitting a fix which addresses the issue by skipping any zero words existing above the highest set bit. In many cases, this also reduces the amount of memory allocated to the resulting
BitSet.@julienrf