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Faulty implementation of method diff in subclass BitSetN of scala.collection.immutable.BitSet #10238

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Dec 19, 2022
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Faulty implementation of method diff in subclass BitSetN of scala.collection.immutable.BitSet #10238

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106 changes: 62 additions & 44 deletions src/library/scala/collection/immutable/BitSet.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -244,36 +244,45 @@ object BitSet extends SpecificIterableFactory[Int, BitSet] {
anyChanges ||= currentWord != oldWord
i -= 1
}
if (i < 0) {
// all indices >= 0 have had result 0, so the bitset is empty
this.empty
} else {
val minimumNonZeroIndex: Int = i + 1
while (!anyChanges && i >= 0) {
val oldWord = word(i)
currentWord = oldWord & ~bs.word(i)
anyChanges ||= currentWord != oldWord
i -= 1
}
if (anyChanges) {
if (minimumNonZeroIndex == -1) {
this.empty
} else if (minimumNonZeroIndex == 0) {
new BitSet1(currentWord)
} else if (minimumNonZeroIndex == 1) {
new BitSet2(word(0) & ~bs.word(0), currentWord)
i match {
case -1 =>
if (anyChanges) {
if (currentWord == 0) {
this.empty
} else {
new BitSet1(currentWord)
}
} else {
this
}
case 0 =>
val oldFirstWord = word(0)
val firstWord = oldFirstWord & ~bs.word(0)
anyChanges ||= firstWord != oldFirstWord
if (anyChanges) {
new BitSet2(firstWord, currentWord)
} else {
this
}
case _ =>
val minimumNonZeroIndex: Int = i + 1
while (!anyChanges && i >= 0) {
val oldWord = word(i)
currentWord = oldWord & ~bs.word(i)
anyChanges ||= currentWord != oldWord
i -= 1
}
if (anyChanges) {
val newArray = elems.take(minimumNonZeroIndex + 1)
newArray(i + 1) = currentWord
while (i >= 0) {
newArray(i) = word(i) & ~bs.word(i)
i -= 1
}
this.fromBitMaskNoCopy(newArray)
new BitSetN(newArray)
} else {
this
}
} else {
this
}
}
} else {
var i = bsnwords - 1
Expand Down Expand Up @@ -314,36 +323,45 @@ object BitSet extends SpecificIterableFactory[Int, BitSet] {
anyChanges ||= currentWord != oldWord
i -= 1
}
if (i < 0) {
// all indices >= 0 have had result 0, so the bitset is empty
if (currentWord == 0) this.empty else this.fromBitMaskNoCopy(Array(currentWord))
} else {
val minimumNonZeroIndex: Int = i + 1
while (!anyChanges && i >= 0) {
val oldWord = word(i)
currentWord = BitSetOps.computeWordForFilter(pred, isFlipped, oldWord, i)
anyChanges ||= currentWord != oldWord
i -= 1
}
if (anyChanges) {
if (minimumNonZeroIndex == -1) {
this.empty
} else if (minimumNonZeroIndex == 0) {
new BitSet1(currentWord)
} else if (minimumNonZeroIndex == 1) {
new BitSet2(BitSetOps.computeWordForFilter(pred, isFlipped, word(0), 0), currentWord)
i match {
case -1 =>
if (anyChanges) {
if (currentWord == 0) {
this.empty
} else {
new BitSet1(currentWord)
}
} else {
this
}
case 0 =>
val oldFirstWord = word(0)
val firstWord = BitSetOps.computeWordForFilter(pred, isFlipped, oldFirstWord, 0)
anyChanges ||= firstWord != oldFirstWord
if (anyChanges) {
new BitSet2(firstWord, currentWord)
} else {
this
}
case _ =>
val minimumNonZeroIndex: Int = i + 1
while (!anyChanges && i >= 0) {
val oldWord = word(i)
currentWord = BitSetOps.computeWordForFilter(pred, isFlipped, oldWord, i)
anyChanges ||= currentWord != oldWord
i -= 1
}
if (anyChanges) {
val newArray = elems.take(minimumNonZeroIndex + 1)
newArray(i + 1) = currentWord
while (i >= 0) {
newArray(i) = BitSetOps.computeWordForFilter(pred, isFlipped, word(i), i)
i -= 1
}
this.fromBitMaskNoCopy(newArray)
new BitSetN(newArray)
} else {
this
}
} else {
this
}
}
}

Expand Down
13 changes: 13 additions & 0 deletions test/junit/scala/collection/immutable/SetTest.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -160,4 +160,17 @@ class SetTest {
testCorrectness()
testNoHashCodeInvocationsDuringSubsetOf()
}

@Test def pr10238(): Unit = {
assertEquals(BitSet(0), BitSet(0, 128) diff BitSet(128))

val us = scala.collection.immutable.BitSet(39, 41, 44, 46, 256)
val vs = scala.collection.immutable.BitSet(39, 41, 44, 46, 64, 256)
val xs = scala.collection.immutable.BitSet.fromBitMask(us.toBitMask.take(3))
val ys = scala.collection.immutable.BitSet.fromBitMask(vs.toBitMask.take(3))
val diff = ys diff xs
val expected = scala.collection.immutable.BitSet(64)
assertEquals(diff, expected)
}

}