Merge pull request #4865 from dotty-staging/fix-tasty-hash

Fix tasty hash

Author: nicolasstucki

compiler/src/dotty/tools/dotc/core/tasty/TastyHash.scala

@@ -0,0 +1,23 @@
+package dotty.tools.dotc.core.tasty
+
+object TastyHash {
+
+  /** Returns a non-cryptographic 64-bit hash of the array.
+   *
+   *  from https://en.wikipedia.org/wiki/PJW_hash_function#Algorithm
+   */
+  def pjwHash64(data: Array[Byte]): Long = {
+    var h = 0L
+    var i = 0
+    while (i < data.length) {
+      val d = data(i) & 0xFFL // Interpret byte as unsigned byte
+      h = (h << 8) + d
+      val high = h & 0xFF00000000000000L
+      h ^= high >>> 48L
+      h &= ~high
+      i += 1
+    }
+    h
+  }
+
+}

compiler/src/dotty/tools/dotc/core/tasty/TastyPickler.scala

@@ -20,13 +20,19 @@ class TastyPickler(val rootCls: ClassSymbol) {
     sections += ((nameBuffer.nameIndex(name.toTermName), buf))
 
   def assembleParts(): Array[Byte] = {
-    def lengthWithLength(buf: TastyBuffer) = {
-      buf.assemble()
+    def lengthWithLength(buf: TastyBuffer) =
       buf.length + natSize(buf.length)
-    }
 
-    val uuidLow: Long = pjwHash64(nameBuffer.bytes)
-    val uuidHi: Long = sections.iterator.map(x => pjwHash64(x._2.bytes)).fold(0L)(_ ^ _)
+    nameBuffer.assemble()
+    sections.foreach(_._2.assemble())
+
+    val nameBufferHash = TastyHash.pjwHash64(nameBuffer.bytes)
+    val treeSectionHash +: otherSectionHashes = sections.map(x => TastyHash.pjwHash64(x._2.bytes))
+
+    // Hash of name table and tree
+    val uuidLow: Long = nameBufferHash ^ treeSectionHash
+    // Hash of positions, comments and any additional section
+    val uuidHi: Long = otherSectionHashes.fold(0L)(_ ^ _)
 
     val headerBuffer = {
       val buf = new TastyBuffer(header.length + 24)
@@ -72,21 +78,4 @@ class TastyPickler(val rootCls: ClassSymbol) {
 
   val treePkl = new TreePickler(this)
 
-  /** Returns a non-cryptographic 64-bit hash of the array.
-   *
-   *  from https://en.wikipedia.org/wiki/PJW_hash_function#Implementation
-   */
-  private def pjwHash64(data: Array[Byte]): Long = {
-    var h = 0L
-    var high = 0L
-    var i = 0
-    while (i < data.length) {
-      h = (h << 4) + data(i)
-      high = h & 0xF0000000L
-      h ^= high >> 24
-      h &= ~high
-      i += 1
-    }
-    h
-  }
 }

compiler/test/dotty/tools/dotc/TastyHashTest.scala

@@ -0,0 +1,29 @@
+package dotty.tools.dotc
+
+import org.junit.Test
+import org.junit.Assert.assertEquals
+
+import dotty.tools.dotc.core.tasty.TastyHash.pjwHash64
+
+class TastyHashTest {
+  @Test def pjwHash64Tests(): Unit = {
+    testHash(0L, Array.empty)
+    testHash(0L, Array(0))
+    testHash(1L, Array(1))
+    testHash(0x7fL, Array(Byte.MaxValue))
+    testHash(0x80L, Array(Byte.MinValue))
+    testHash(0x101L, Array(1, 1))
+    testHash(0X10101L, Array(1, 1, 1))
+    testHash(0X1010101L, Array(1, 1, 1, 1))
+    testHash(0X101010101L, Array(1, 1, 1, 1, 1))
+    testHash(0X202020202L, Array(2, 2, 2, 2, 2))
+    testHash(0X1010101L, Array.fill(1024)(1))
+    testHash(0xaafefeaaab54ffL, Array.tabulate(1024)(_.toByte))
+    testHash(0x34545c16020230L, "abcdefghijklmnopqrstuvwxyz1234567890".getBytes)
+  }
+
+  def testHash(expected: Long, arr: Array[Byte]): Unit = {
+    assertEquals(s"0x${expected.toHexString}L", s"0x${pjwHash64(arr).toHexString}L")
+  }
+
+}