Added size hints to Array.{ iterate, range, tab...

Added size hints to Array.{ iterate, range, tabulate, fill }.
Probably closes #3331, but it would be nice if someone would measure
whether it makes much difference to skip the builder entirely in
those cases where that could be done.  No review.

2 files changed, 22 insertions, 0 deletions

diff --git a/src/library/scala/Array.scala b/src/library/scala/Array.scala
index f89e8b48a5..c9d929b88c 100644
--- a/src/library/scala/Array.scala
+++ b/src/library/scala/Array.scala
@@ -207,6 +207,7 @@ object Array extends FallbackArrayBuilding {
    */
   def fill[T: ClassManifest](n: Int)(elem: => T): Array[T] = {
     val b = newBuilder[T]
+    b.sizeHint(n)
     var i = 0
     while (i < n) {
       b += elem
@@ -270,6 +271,7 @@ object Array extends FallbackArrayBuilding {
    */
   def tabulate[T: ClassManifest](n: Int)(f: Int => T): Array[T] = {
     val b = newBuilder[T]
+    b.sizeHint(n)
     var i = 0
     while (i < n) {
       b += f(i)
@@ -343,6 +345,8 @@ object Array extends FallbackArrayBuilding {
   def range(start: Int, end: Int, step: Int): Array[Int] = {
     if (step == 0) throw new IllegalArgumentException("zero step")
     val b = newBuilder[Int]
+    b.sizeHint(Range.count(start, end, step, false))
+
     var i = start
     while (if (step < 0) end < i else i < end) {
       b += i
@@ -360,6 +364,7 @@ object Array extends FallbackArrayBuilding {
    */
   def iterate[T: ClassManifest](start: T, len: Int)(f: T => T): Array[T] = {
     val b = newBuilder[T]
+    b.sizeHint(len)
     var acc = start
     var i = 0
     while (i < len) {
diff --git a/src/library/scala/collection/immutable/Range.scala b/src/library/scala/collection/immutable/Range.scala
index 8f1f7d58a6..0f20b1ea04 100644
--- a/src/library/scala/collection/immutable/Range.scala
+++ b/src/library/scala/collection/immutable/Range.scala
@@ -219,6 +219,23 @@ class Range(val start: Int, val end: Int, val step: Int) extends IndexedSeq[Int]
 object Range {
   private[immutable] val MAX_PRINT = 512  // some arbitrary value
 
+  /** Calculates the number of elements in a range given start, end, step, and
+   *  whether or not it is inclusive.  Returns -1 if parameters are invalid.
+   */
+  def count(start: Int, end: Int, step: Int): Int = count(start, end, step, false)
+  def count(start: Int, end: Int, step: Int, isInclusive: Boolean): Int = {
+    def last =
+      if (isInclusive && step < 0) end - 1
+      else if (isInclusive && step > 0) end + 1
+      else end
+
+    if (step == 0) -1
+    else if (start == end) { if (isInclusive) 1 else 0 }
+    else if (end > start != step > 0) -1
+    else if (step == 1 || step == -1) last - start
+    else ((last - start - 1) / step) + 1
+  }
+
   class Inclusive(start: Int, end: Int, step: Int) extends Range(start, end, step) {
     override def isInclusive = true
     override protected def copy(start: Int, end: Int, step: Int): Range = new Inclusive(start, end, step)