SI-9059 Random.alphanumeric is inefficient

Generate alphanumeric values by taking random element of string
containing all alphanumerics.

Instead of generating nextPrintableChar then filtering for
alphanumerics, we can just take from a string containing all
alphanumerics.  This provides a significant performance improvement.

1 files changed, 8 insertions, 2 deletions

diff --git a/src/library/scala/util/Random.scala b/src/library/scala/util/Random.scala
index 8d68c5be38..2d38c9d4a0 100644
--- a/src/library/scala/util/Random.scala
+++ b/src/library/scala/util/Random.scala
@@ -121,15 +121,21 @@ class Random(val self: java.util.Random) extends AnyRef with Serializable {
     (bf(xs) ++= buf).result()
   }
 
+  @deprecated("Preserved for backwards binary compatibility. To remove in 2.12.x.", "2.11.6")
+  final def `scala$util$Random$$isAlphaNum$1`(c: Char) = (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') || (c >= '0' && c <= '9')
+
   /** Returns a Stream of pseudorandomly chosen alphanumeric characters,
    *  equally chosen from A-Z, a-z, and 0-9.
    *
    *  @since 2.8
    */
   def alphanumeric: Stream[Char] = {
-    def isAlphaNum(c: Char) = (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') || (c >= '0' && c <= '9')
+    def nextAlphaNum: Char = {
+      val chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
+      chars charAt (self nextInt chars.length)
+    }
 
-    Stream continually nextPrintableChar filter isAlphaNum
+    Stream continually nextAlphaNum
   }
 
 }