diff options
Diffstat (limited to 'src')
-rw-r--r-- | src/library/scala/collection/immutable/Range.scala | 89 | ||||
-rw-r--r-- | src/library/scala/collection/parallel/immutable/ParRange.scala | 2 |
2 files changed, 78 insertions, 13 deletions
diff --git a/src/library/scala/collection/immutable/Range.scala b/src/library/scala/collection/immutable/Range.scala index e891f8bec8..16d7e68dee 100644 --- a/src/library/scala/collection/immutable/Range.scala +++ b/src/library/scala/collection/immutable/Range.scala @@ -71,18 +71,6 @@ extends collection.AbstractSeq[Int] def isInclusive = false - @inline final override def foreach[@specialized(Unit) U](f: Int => U) { - if (length > 0) { - val last = this.last - var i = start - while (i != last) { - f(i) - i += step - } - f(i) - } - } - override def length: Int = numRangeElements override lazy val last: Int = if (length == 0) Nil.last @@ -95,6 +83,83 @@ extends collection.AbstractSeq[Int] if (idx < 0 || idx >= length) throw new IndexOutOfBoundsException(idx.toString) locationAfterN(idx) } + + /** @note Making foreach run as fast as a while loop is a challenge. + * The key elements which I can observe making a difference are: + * + * - the inner loop should be as small as possible + * - the inner loop should be monomorphic + * - the inner loop should perform no boxing and no avoidable tests + * + * This is achieved by: + * + * - keeping initialization logic out of the inner loop + * - dispatching to custom variations based on initial conditions + * - tricking the compiler into always calling Function1#apply$mcVI$sp + * + * The last one is important and less than obvious. Even when foreach + * was specialized on Unit, only Int => Unit arguments benefited from it. + * Other function types would be accepted, but in the absence of full + * specialization the integer argument was boxed on every call. For example: + * + class A { + final def f(x: Int): Int = x + 1 + // Calls Range.foreach, which calls Function1.apply + def g1 = 1 until 100 foreach { x => f(x) } + // Calls Range.foreach$mVc$sp, which calls Function1.apply$mcVI$sp + def g2 = 1 until 100 foreach { x => f(x) ; () } + } + * + * However! Since the result of the closure is always discarded, we + * simply cast it to Int => Unit, thereby executing the fast version. + * The seemingly looming ClassCastException can never arrive. + */ + @inline final override def foreach[U](f: Int => U) { + if (step < 0) { + if (isInclusive) foreachDownIn(f.asInstanceOf[Int => Unit]) + else foreachDownEx(f.asInstanceOf[Int => Unit]) + } + else { + if (isInclusive) foreachUpIn(f.asInstanceOf[Int => Unit]) + else foreachUpEx(f.asInstanceOf[Int => Unit]) + } + } + + /** !!! These methods must be public or they will not be inlined. + * But they are certainly not intended to be part of the API. + * This collision between inlining requirements and access semantics + * is highly unfortunate and must be resolved. + * + * Proposed band-aid: an @internal annotation. + */ + @inline final def foreachDownIn(f: Int => Unit) { + var i = start + while (i >= end) { + f(i) + i += step + } + } + @inline final def foreachUpIn(f: Int => Unit) { + var i = start + while (i <= end) { + f(i) + i += step + } + } + @inline final def foreachDownEx(f: Int => Unit) { + var i = start + while (i > end) { + f(i) + i += step + } + } + @inline final def foreachUpEx(f: Int => Unit) { + var i = start + while (i < end) { + f(i) + i += step + } + } /** Creates a new range containing the first `n` elements of this range. * diff --git a/src/library/scala/collection/parallel/immutable/ParRange.scala b/src/library/scala/collection/parallel/immutable/ParRange.scala index 2a10458457..350e64739f 100644 --- a/src/library/scala/collection/parallel/immutable/ParRange.scala +++ b/src/library/scala/collection/parallel/immutable/ParRange.scala @@ -88,7 +88,7 @@ self => /* accessors */ override def foreach[U](f: Int => U): Unit = { - rangeleft.foreach(f) + rangeleft.foreach(f.asInstanceOf[Int => Unit]) ind = len } |