From 13643815fe41b17e931be9d0a8906200b0147a23 Mon Sep 17 00:00:00 2001
From: Paul Phillips <paulp@improving.org>
Date: Fri, 28 Dec 2012 16:52:47 -0800
Subject: LinearSeq lengthCompare without an iterator.

Had to fix up an iffy test: not only was it testing undefined
behavior, it demanded just the right numbers be printed in a
context where all negative or positive numbers are equivalent.
It's the ol' "get them coming and going" trick.
---
 .../scala/collection/LinearSeqOptimized.scala      | 22 ++++++++++------------
 test/files/run/t2544.check                         |  4 ++--
 test/files/run/t2544.scala                         | 22 ++++++++++++++--------
 3 files changed, 26 insertions(+), 22 deletions(-)

diff --git a/src/library/scala/collection/LinearSeqOptimized.scala b/src/library/scala/collection/LinearSeqOptimized.scala
index 48b0b5469e..81cccea519 100755
--- a/src/library/scala/collection/LinearSeqOptimized.scala
+++ b/src/library/scala/collection/LinearSeqOptimized.scala
@@ -12,6 +12,7 @@ import generic._
 import mutable.ListBuffer
 import immutable.List
 import scala.util.control.Breaks._
+import scala.annotation.tailrec
 
 /** A template trait for linear sequences of type `LinearSeq[A]`  which optimizes
  *  the implementation of several methods under the assumption of fast linear access.
@@ -248,19 +249,16 @@ trait LinearSeqOptimized[+A, +Repr <: LinearSeqOptimized[A, Repr]] extends Linea
 
   override /*SeqLike*/
   def lengthCompare(len: Int): Int = {
-    // TODO: Remove this method when incrementing a major revision
-    // This method is the same as in SeqLike, no need to redefine it
-    if (len < 0) 1
-    else {
-      var i = 0
-      val it = iterator
-      while (it.hasNext) {
-        if (i == len) return if (it.hasNext) 1 else 0
-        it.next()
-        i += 1
-      }
-      i - len
+    @tailrec def loop(i: Int, xs: Repr): Int = {
+      if (i == len)
+        if (xs.isEmpty) 0 else 1
+      else if (xs.isEmpty)
+        -1
+      else
+        loop(i + 1, xs.tail)
     }
+    if (len < 0) 1
+    else loop(0, this)
   }
 
   override /*SeqLike*/
diff --git a/test/files/run/t2544.check b/test/files/run/t2544.check
index 716b146ac4..d19538dca3 100644
--- a/test/files/run/t2544.check
+++ b/test/files/run/t2544.check
@@ -2,8 +2,8 @@
 2
 3
 3
--2
--2
+-1
+-1
 1
 1
 0
diff --git a/test/files/run/t2544.scala b/test/files/run/t2544.scala
index 7e7cfeb357..6bee2f1082 100644
--- a/test/files/run/t2544.scala
+++ b/test/files/run/t2544.scala
@@ -1,19 +1,25 @@
 object Test {
   object Foo extends Seq[Int] {
     def apply(i: Int) = i
-    def length = 4
+    def length = 5
     def iterator = Iterator(0,1,2,3,4)
   }
+  def lengthEquiv(result: Int) = println(
+    if (result < 0) -1
+    else if (result == 0) 0
+    else 1
+  )
+
   def main(args: Array[String]) = {
     println(Foo indexWhere(_ >= 2,1))
     println(Foo.toList indexWhere(_ >= 2,1))
     println(Foo segmentLength(_ <= 3,1))
     println(Foo.toList segmentLength(_ <= 3,1))
-    println(Foo lengthCompare 7)
-    println(Foo.toList lengthCompare 7)
-    println(Foo lengthCompare 2)
-    println(Foo.toList lengthCompare 2)
-    println(Foo lengthCompare 5)
-    println(Foo.toList lengthCompare 5)
+    lengthEquiv(Foo lengthCompare 7)
+    lengthEquiv(Foo.toList lengthCompare 7)
+    lengthEquiv(Foo lengthCompare 2)
+    lengthEquiv(Foo.toList lengthCompare 2)
+    lengthEquiv(Foo lengthCompare 5)
+    lengthEquiv(Foo.toList lengthCompare 5)
   }
-}
\ No newline at end of file
+}
-- 
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