SI-9388 Fix Range behavior around Int.MaxValue

terminalElement (the element _after_ the last one!) was used to terminate foreach loops and sums of non-standard instances of Numeric.  Unfortunately, this could result in the end wrapping around and hitting the beginning again, making the first element bad.

This patch fixes the behavior by altering the loop to end after the last element is encountered.  The particular flavor was chosen out of a few possibilities because it gave the best microbenchmarks on both large and small ranges.

Test written.  While testing, a bug was also uncovered in NumericRange, and was also fixed.  In brief, the logic around sum is rather complex since division is not unique when you have overflow.  Floating point has its own complexities, too.

Also updated incorrect test t4658 that insisted on incorrect answers (?!) and added logic to make sure it at least stays self-consistent, and fixed the range.scala test which used the same wrong (overflow-prone) formula that the Range collection did.

4 files changed, 55 insertions, 4 deletions

diff --git a/test/files/run/t4658.check b/test/files/run/t4658.check
index bb6405175e..3bc52daef3 100644
--- a/test/files/run/t4658.check
+++ b/test/files/run/t4658.check
@@ -1,5 +1,5 @@
 Ranges:
-1073741824
+-1073741824
 1073741824
 0
 0
@@ -20,7 +20,7 @@ Ranges:
 -10
 IntRanges:
 -1073741824
--1073741824
+1073741824
 0
 0
 55
@@ -78,3 +78,6 @@ BigIntRanges:
 -24
 -30
 -10
+BigInt agrees with Long: true
+Long agrees with Int when rounded: true
+Numeric Int agrees with Range: true
diff --git a/test/files/run/t4658.scala b/test/files/run/t4658.scala
index 8c07c50694..7fc6d4584c 100644
--- a/test/files/run/t4658.scala
+++ b/test/files/run/t4658.scala
@@ -2,6 +2,7 @@ import scala.collection.immutable.NumericRange
 //#4658
 object Test {
 
+  // Only works for Int values!  Need to rethink explicit otherwise.
   case class R(start: Int, end: Int, step: Int = 1, inclusive: Boolean = true)
 
   val rangeData = Array(
@@ -28,6 +29,14 @@ object Test {
     numericLongRanges.foreach{range => println(range.sum)}
     println("BigIntRanges:")
     numericBigIntRanges.foreach{range => println(range.sum)}
+    println("BigInt agrees with Long: " + 
+      (numericLongRanges zip numericBigIntRanges).forall{ case (lr, bir) => lr.sum == bir.sum }
+    )
+    println("Long agrees with Int when rounded: " + 
+      (numericLongRanges zip numericIntRanges).forall{ case (lr, ir) => lr.sum.toInt == ir.sum }
+    )
+    println("Numeric Int agrees with Range: " +
+      (numericIntRanges zip ranges).forall{ case (ir, r) => ir.sum == r.sum }
+    )
   }
-
 }
\ No newline at end of file
diff --git a/test/files/scalacheck/range.scala b/test/files/scalacheck/range.scala
index 493083a51f..ac24b52f8d 100644
--- a/test/files/scalacheck/range.scala
+++ b/test/files/scalacheck/range.scala
@@ -134,7 +134,22 @@ abstract class RangeTest(kind: String) extends Properties("Range "+kind) {
     val expected = r.length match {
       case 0 => 0
       case 1 => r.head
-      case _ => ((r.head + r.last).toLong * r.length  / 2).toInt
+      case x if x < 1000 => 
+        // Explicit sum, to guard against having the same mistake in both the
+        // range implementation and test implementation of sum formula.
+        // (Yes, this happened before.)
+        var i = r.head
+        var s = 0L
+        var n = x
+        while (n > 0) {
+          s += i
+          i += r.step
+          n -= 1
+        }
+        s.toInt
+      case _ =>
+        // Make sure head + last doesn't overflow!
+        ((r.head.toLong + r.last) * r.length  / 2).toInt
     }
 //   println("size: " + r.length)
 //   println("expected: " + expected)
diff --git a/test/junit/scala/collection/immutable/RangeConsistencyTest.scala b/test/junit/scala/collection/immutable/RangeConsistencyTest.scala
index 135796979d..760498c162 100644
--- a/test/junit/scala/collection/immutable/RangeConsistencyTest.scala
+++ b/test/junit/scala/collection/immutable/RangeConsistencyTest.scala
@@ -148,4 +148,28 @@ class RangeConsistencyTest {
     val bdRange = bd(-10.0) until bd(0.0) by bd(4.5)
     assert( bdRange sameElements List(bd(-10.0), bd(-5.5), bd(-1.0)) )
   }
+
+  @Test
+  def test_SI9388()  {
+    val possiblyNotDefaultNumeric = new scala.math.Numeric[Int] {
+      def fromInt(x: Int) = x
+      def minus(x: Int, y: Int): Int = x - y
+      def negate(x: Int): Int = -x
+      def plus(x: Int, y: Int): Int = x + y
+      def times(x: Int, y: Int): Int = x*y
+      def toDouble(x: Int): Double = x.toDouble
+      def toFloat(x: Int): Float = x.toFloat
+      def toInt(x: Int): Int = x
+      def toLong(x: Int): Long = x.toLong
+      def compare(x: Int, y: Int) = x compare y
+    }
+    val r = (Int.MinValue to Int.MaxValue by (1<<23))
+    val nr = NumericRange(Int.MinValue, Int.MaxValue, 1 << 23)
+    assert({ var i = 0; r.foreach(_ => i += 1); i } == 512)
+    assert({ var i = 0; nr.foreach(_ => i += 1); i } == 512)
+    assert(r.sum == Int.MinValue)
+    assert(nr.sum == Int.MinValue)
+    assert(r.sum(possiblyNotDefaultNumeric) == Int.MinValue)
+    assert(nr.sum(possiblyNotDefaultNumeric) == Int.MinValue)
+  }
 }