Add pjwHash64 regression tests

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

@@ -26,8 +26,8 @@ class TastyPickler(val rootCls: ClassSymbol) {
     nameBuffer.assemble()
     sections.foreach(_._2.assemble())
 
-    val nameBufferHash = pjwHash64(nameBuffer.bytes)
-    val treeSectionHash +: otherSectionHashes = sections.map(x => pjwHash64(x._2.bytes))
+    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
@@ -78,21 +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#Algorithm
-   */
-  private 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
-  }
 }

tests/run-with-compiler/tasty-hash.scala

@@ -0,0 +1,25 @@
+import dotty.tools.dotc.core.tasty.TastyHash.pjwHash64
+
+object Test {
+  def main(args: Array[String]): 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(0X55aa01fe55ab54ffL, Array.tabulate(1024)(_.toByte))
+    testHash(0x34545c16020230L, "abcdefghijklmnopqrstuvwxyz1234567890".getBytes)
+  }
+
+  def testHash(expected: Long, arr: Array[Byte]): Unit = {
+    val res = pjwHash64(arr)
+    assert(res == expected, s"Exprected 0x${expected.toHexString}L but got 0X${res.toHexString}L")
+  }
+
+}