SI-7443 Use typeclass instance for {Range,NumericRange}.sum

Previously both Range and NumeriRange used formula for sum of elements
of arithmetic series and thus always assumed that provided Numeric is
regular one.
Bug is now fixed by conservatively checking if Numeric is one of
default ones and the formula still holds.

1 files changed, 41 insertions, 0 deletions

diff --git a/test/files/scalacheck/range.scala b/test/files/scalacheck/range.scala
index 6c7c32bfdf..1eb186f303 100644
--- a/test/files/scalacheck/range.scala
+++ b/test/files/scalacheck/range.scala
@@ -127,6 +127,47 @@ abstract class RangeTest(kind: String) extends Properties("Range "+kind) {
     (visited == expectedSize(r)) :| str(r)
   }
 
+  property("sum") = forAll(myGen) { r =>
+//    println("----------")
+//    println("sum "+str(r))
+    val rSum = r.sum
+    val expected = r.length match {
+      case 0 => 0
+      case 1 => r.head
+      case _ => ((r.head + r.last).toLong * r.length  / 2).toInt
+    }
+//   println("size: " + r.length)
+//   println("expected: " + expected)
+//   println("obtained: " + rSum)
+
+   (rSum == expected) :| str(r)
+  }
+
+/* checks that sum respects custom Numeric */
+  property("sumCustomNumeric") = forAll(myGen) { r =>
+    val mod = 65536
+    object mynum extends Numeric[Int] {
+        def plus(x: Int, y: Int): Int = (x + y) % mod
+        override def zero = 0
+
+        def fromInt(x: Int): Int = ???
+        def minus(x: Int, y: Int): Int = ???
+        def negate(x: Int): Int = ???
+        def times(x: Int, y: Int): Int = ???
+        def toDouble(x: Int): Double = ???
+        def toFloat(x: Int): Float = ???
+        def toInt(x: Int): Int = ((x % mod) + mod * 2) % mod
+        def toLong(x: Int): Long = ???
+        def compare(x: Int, y: Int): Int = ???
+      }
+
+    val rSum = r.sum(mynum)
+    val expected = mynum.toInt(r.sum)
+
+    (rSum == expected) :| str(r)
+  }
+
+
   property("length") = forAll(myGen suchThat (r => expectedSize(r).toInt == expectedSize(r))) { r =>
 //    println("length "+str(r))
     (r.length == expectedSize(r)) :| str(r)