scala.collection.mutable.BitSet uses exponentially growing memory under certain conditions.

[scabug]

scala.collection.mutable.BitSet has off-by-one errors in |=, &=, ^=, and &~=. These functions all call ensureCapacity with the size of a list as a parameter, instead of the index of their last values. As a result, elems doubles in size every time these functions are used on two BitSets with the same nwords.

Welcome to Scala version 2.11.2 (OpenJDK 64-Bit Server VM, Java 1.7.0_65).
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scala> val bitSet = new scala.collection.mutable.BitSet()
bitSet: scala.collection.mutable.BitSet = BitSet()

scala> bitSet ^= bitSet; bitSet.toBitMask.length
res0: Int = 2

scala> bitSet ^= bitSet; bitSet.toBitMask.length
res1: Int = 4

scala> bitSet ^= bitSet; bitSet.toBitMask.length
res2: Int = 8

scala> bitSet ^= bitSet; bitSet.toBitMask.length
res3: Int = 16

scala> bitSet ^= bitSet; bitSet.toBitMask.length
res4: Int = 32

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-8910?orig=1
Reporter: Alissa Rao (Lymia)
Affected Versions: 2.11.2

[scabug]

@gourlaysama said:
PR: scala/scala#4052