An overhaul of slice and related implementation...

An overhaul of slice and related implementations (primarily that is
drop and take.) In the course of trying to get it working consistently
(mostly with respect to negative indices, which were dealt with
arbitrarily differently across the 25+ concrete implementations) I fixed
various bugs.

Closes #4288, no review.

1 files changed, 12 insertions, 4 deletions

diff --git a/src/library/scala/collection/LinearSeqOptimized.scala b/src/library/scala/collection/LinearSeqOptimized.scala
index 5e47021110..f57dba2d3f 100755
--- a/src/library/scala/collection/LinearSeqOptimized.scala
+++ b/src/library/scala/collection/LinearSeqOptimized.scala
@@ -183,13 +183,21 @@ trait LinearSeqOptimized[+A, +Repr <: LinearSeqOptimized[A, Repr]] extends Linea
 
   override /*IterableLike*/
   def slice(from: Int, until: Int): Repr = {
+    var these: Repr = repr
+    var count = from max 0
+    if (until <= count)
+      return newBuilder.result
+
     val b = newBuilder
-    var i = from
-    var these = this drop from
-    while (i < until && !these.isEmpty) {
+    var sliceElems = until - count
+    while (these.nonEmpty && count > 0) {
+      these = these.tail
+      count -= 1
+    }
+    while (these.nonEmpty && sliceElems > 0) {
+      sliceElems -= 1
       b += these.head
       these = these.tail
-      i += 1
     }
     b.result
   }