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Implements specialized subsetOf for HashSet
Fixes SI-7326. This also adds a basic test for subsetOf that was missing before.
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import scala.collection.immutable.ListSet | ||
import scala.collection.immutable.HashSet | ||
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object Test extends App { | ||
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def testCorrectness() { | ||
// a key that has many hashCode collisions | ||
case class Collision(i: Int) { override def hashCode = i / 5 } | ||
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def subsetTest[T](emptyA:Set[T], emptyB:Set[T], mkKey:Int => T, n:Int) { | ||
val outside = mkKey(n + 1) | ||
for(i <- 0 to n) { | ||
val a = emptyA ++ (0 until i).map(mkKey) | ||
// every set must be a subset of itself | ||
require(a.subsetOf(a), "A set must be the subset of itself") | ||
for(k <- 0 to i) { | ||
// k <= i, so b is definitely a subset | ||
val b = emptyB ++ (0 until k).map(mkKey) | ||
// c has less elements than a, but contains a value that is not in a | ||
// so it is not a subset, but that is not immediately obvious due to size | ||
val c = b + outside | ||
require(b.subsetOf(a), s"$b must be a subset of $a") | ||
require(!c.subsetOf(a), s"$c must not be a subset of $a") | ||
} | ||
} | ||
} | ||
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// test the HashSet/HashSet case | ||
subsetTest(HashSet.empty[Int], HashSet.empty[Int], identity, 100) | ||
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// test the HashSet/other set case | ||
subsetTest(HashSet.empty[Int], ListSet.empty[Int], identity, 100) | ||
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// test the HashSet/HashSet case for Collision keys | ||
subsetTest(HashSet.empty[Collision], HashSet.empty[Collision], Collision, 100) | ||
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// test the HashSet/other set case for Collision keys | ||
subsetTest(HashSet.empty[Collision], ListSet.empty[Collision], Collision, 100) | ||
} | ||
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/** | ||
* A main performance benefit of the new subsetOf is that we do not have to call hashCode during subsetOf | ||
* since we already have the hash codes in the HashSet1 nodes. | ||
*/ | ||
def testNoHashCodeInvocationsDuringSubsetOf() = { | ||
var count = 0 | ||
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case class HashCodeCounter(i:Int) { | ||
override def hashCode = { | ||
count += 1 | ||
i | ||
} | ||
} | ||
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val a = HashSet.empty ++ (0 until 100).map(HashCodeCounter) | ||
val b = HashSet.empty ++ (0 until 50).map(HashCodeCounter) | ||
val count0 = count | ||
val result = b.subsetOf(a) | ||
require(count == count0, "key.hashCode must not be called during subsetOf of two HashSets") | ||
result | ||
} | ||
testCorrectness() | ||
testNoHashCodeInvocationsDuringSubsetOf() | ||
} |