For size compression, compress non zero values into non zero values.

core/src/main/scala/spark/MapOutputTracker.scala

@@ -2,6 +2,10 @@ package spark
 
 import java.io._
 import java.util.concurrent.ConcurrentHashMap
+import java.util.zip.{GZIPInputStream, GZIPOutputStream}
+
+import scala.collection.mutable.HashMap
+import scala.collection.mutable.HashSet
 
 import akka.actor._
 import akka.dispatch._
@@ -11,12 +15,9 @@ import akka.util.Duration
 import akka.util.Timeout
 import akka.util.duration._
 
-import scala.collection.mutable.HashMap
+import spark.scheduler.MapStatus
-import scala.collection.mutable.HashSet
-
-import scheduler.MapStatus
 import spark.storage.BlockManagerId
-import java.util.zip.{GZIPInputStream, GZIPOutputStream}
+
 
 private[spark] sealed trait MapOutputTrackerMessage
 private[spark] case class GetMapOutputStatuses(shuffleId: Int, requester: String)
@@ -254,8 +255,10 @@ private[spark] object MapOutputTracker {
    * sizes up to 35 GB with at most 10% error.
    */
   def compressSize(size: Long): Byte = {
-    if (size <= 1L) {
+    if (size == 0) {
       0
+    } else if (size <= 1L) {
+      1
     } else {
       math.min(255, math.ceil(math.log(size) / math.log(LOG_BASE)).toInt).toByte
     }
@@ -266,7 +269,7 @@ private[spark] object MapOutputTracker {
    */
   def decompressSize(compressedSize: Byte): Long = {
     if (compressedSize == 0) {
-      1
+      0
     } else {
       math.pow(LOG_BASE, (compressedSize & 0xFF)).toLong
     }

core/src/test/scala/spark/MapOutputTrackerSuite.scala

@@ -5,7 +5,7 @@ import org.scalatest.FunSuite
 class MapOutputTrackerSuite extends FunSuite {
   test("compressSize") {
     assert(MapOutputTracker.compressSize(0L) === 0)
-    assert(MapOutputTracker.compressSize(1L) === 0)
+    assert(MapOutputTracker.compressSize(1L) === 1)
     assert(MapOutputTracker.compressSize(2L) === 8)
     assert(MapOutputTracker.compressSize(10L) === 25)
     assert((MapOutputTracker.compressSize(1000000L) & 0xFF) === 145)
@@ -15,7 +15,7 @@ class MapOutputTrackerSuite extends FunSuite {
   }
 
   test("decompressSize") {
-    assert(MapOutputTracker.decompressSize(0) === 1)
+    assert(MapOutputTracker.decompressSize(0) === 0)
     for (size <- Seq(2L, 10L, 100L, 50000L, 1000000L, 1000000000L)) {
       val size2 = MapOutputTracker.decompressSize(MapOutputTracker.compressSize(size))
       assert(size2 >= 0.99 * size && size2 <= 1.11 * size,