Applied patch for #2524.

2 files changed, 28 insertions, 3 deletions

diff --git a/src/library/scala/collection/mutable/HashTable.scala b/src/library/scala/collection/mutable/HashTable.scala
index 6726a3dbbc..9d3a35376c 100644
--- a/src/library/scala/collection/mutable/HashTable.scala
+++ b/src/library/scala/collection/mutable/HashTable.scala
@@ -45,12 +45,27 @@ trait HashTable[A] {
 
   /** The initial threshold
    */
-  protected def initialThreshold: Int = newThreshold(initialSize)
+  protected def initialThreshold: Int = newThreshold(initialCapacity)
 
   /** The actual hash table.
    */
-  protected var table: Array[HashEntry[A, Entry]] =
-    if (initialSize == 0) null else new Array(initialSize)
+  protected var table: Array[HashEntry[A, Entry]] = new Array(initialCapacity)
+
+  private def initialCapacity = if (initialSize == 0) 1 else powerOfTwo(initialSize)
+
+  /**
+   * Returns a power of two >= `target`.
+   */
+  private def powerOfTwo(target: Int): Int = {
+    /* See http://bits.stephan-brumme.com/roundUpToNextPowerOfTwo.html */
+    var c = target - 1;
+    c |= c >>>  1;
+    c |= c >>>  2;
+    c |= c >>>  4;
+    c |= c >>>  8;
+    c |= c >>> 16;
+    c + 1;
+  }
 
   /** The number of mappings contained in this hash table.
    */
diff --git a/test/files/run/t2524.scala b/test/files/run/t2524.scala
new file mode 100644
index 0000000000..552663e9e8
--- /dev/null
+++ b/test/files/run/t2524.scala
@@ -0,0 +1,10 @@
+object Test {
+  def main(args: Array[String]) {
+    val m = new collection.mutable.HashMap[String, String] {
+      override def initialSize = 0
+    }
+    m.toString
+    m("key") = "value"
+    assert(m("key") == "value")
+  }
+}