[CODEC-269] Allow repeat calls to IncrementalHash32.end().

aherbert · aherbert · commit 1490fbf959fc · 2019-11-21T14:16:03.000Z
Repeat calls with no additional data should create the same hash.
diff --git a/src/changes/changes.xml b/src/changes/changes.xml
@@ -42,9 +42,13 @@ The <action> type attribute can be add,update,fix,remove.
   </properties>
   <body>
 
+    <release version="1.14" date="TBD" description="Feature and fix release.">
+      <action issue="CODEC-269" dev="aherbert" type="fix">Allow repeat calls to IncrementalHash32.end() to generate the same value.</action>
+    </release>
+
     <release version="1.13" date="2019-07-20" description="Feature and fix release.">
-      <action issue="CODEC-255" dev="sebb" due-to="Holger Grote" type="fix">ColognePhonetic handles x incorrectly</action>      
-      <action issue="CODEC-254" dev="sebb" due-to="Holger Grote" type="fix">ColognePhonetic does not treat the letter H correctly</action>      
+      <action issue="CODEC-255" dev="sebb" due-to="Holger Grote" type="fix">ColognePhonetic handles x incorrectly</action>
+      <action issue="CODEC-254" dev="sebb" due-to="Holger Grote" type="fix">ColognePhonetic does not treat the letter H correctly</action>
       <action issue="CODEC-134" dev="tmousaw-ptc" type="fix">Reject any decode request for a value that is impossible to encode to for Base32/Base64 rather than blindly decoding.</action>
       <action issue="CODEC-236" dev="melloware" due-to="Viliam Holub" type="add">MurmurHash2 for 32-bit or 64-bit value.</action>
       <action issue="CODEC-236" dev="melloware" due-to="Austin Appleby" type="add">MurmurHash3 for 32-bit or 128-bit value.</action>
diff --git a/src/main/java/org/apache/commons/codec/digest/MurmurHash3.java b/src/main/java/org/apache/commons/codec/digest/MurmurHash3.java
@@ -923,6 +923,8 @@ public final void add(final byte[] data, final int offset, final int length) {
          * @return The 32-bit hash
          */
         public final int end() {
+            // Allow calling end() again after adding no data to return the same result.
+            int result = hash;
             // ************
             // Note: This fails to apply masking using 0xff to the 3 remaining bytes.
             // ************
@@ -939,12 +941,12 @@ public final int end() {
                 k1 *= C1_32;
                 k1 = Integer.rotateLeft(k1, R1_32);
                 k1 *= C2_32;
-                hash ^= k1;
+                result ^= k1;
             }
 
             // finalization
-            hash ^= totalLen;
-            return fmix32(hash);
+            result ^= totalLen;
+            return fmix32(result);
         }
 
         /**
diff --git a/src/test/java/org/apache/commons/codec/digest/MurmurHash3Test.java b/src/test/java/org/apache/commons/codec/digest/MurmurHash3Test.java
@@ -597,6 +597,7 @@ private static void assertIncrementalHash32(byte[] bytes, int seed, int... block
             offset += block;
             final int h2 = inc.end();
             Assert.assertEquals("Hashes differ", h1, h2);
+            Assert.assertEquals("Hashes differ after no additional data", h1, inc.end());
         }
     }
 }

Original file line number	Diff line number	Diff line change
`@@ -597,6 +597,7 @@ private static void assertIncrementalHash32(byte[] bytes, int seed, int... block`
`597`	`597`	`offset += block;`
`598`	`598`	`final int h2 = inc.end();`
`599`	`599`	`Assert.assertEquals("Hashes differ", h1, h2);`
	`600`	`+ Assert.assertEquals("Hashes differ after no additional data", h1, inc.end());`
`600`	`601`	`}`
`601`	`602`	`}`
`602`	`603`	`}`