Description
A non-empty bitset incorrectly raises an "Empty BitSet" exception. The exception occurs several seconds after invoking the method.
scala> scala.collection.mutable.BitSet() ++ (0 to 128)
res9: scala.collection.mutable.BitSet = BitSet(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128)
scala> res9.last
java.util.NoSuchElementException: Empty BitSet
at scala.collection.BitSetLike.last(BitSetLike.scala:225)
at scala.collection.BitSetLike.last$(BitSetLike.scala:218)
at scala.collection.mutable.BitSet.last(BitSet.scala:40)
... 30 elided
I think that the cause is this line from the source code (link to line 223 of BitSetLike.scala).
Based on the loop termination condition, the loop looks like it is meant to walk backwards through the array of words. And this is what you would expect for "last"
But the index variable "i" is being incremented.
I believe that what is happening in the example above is that "i" is being incremented until it overflows to MIN_INT (this takes several seconds on my machine) - and then the loop terminates and the exception is thrown.
(0 to 128) seems to be the smallest example on which this fails. (0 to 127) is fine.