Improve error message for hash collisions, tune tertiary slot sizes

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/core/sym/ByteQuadsCanonicalizer.java

@@ -1016,9 +1016,9 @@ public int calcHash(int q1, int q2, int q3)
     { // use same algorithm as multi-byte, tested to work well
         int hash = q1 ^ _seed;
         hash += (hash >>> 9);
-        hash *= MULT;
+        hash *= MULT3;
         hash += q2;
-        hash *= MULT2;
+        hash *= MULT;
         hash += (hash >>> 15);
         hash ^= q3;
         // 26-Mar-2015, tatu: As per two-quad case, a short shift seems to help more here
@@ -1183,13 +1183,14 @@ private final int _spilloverStart() {
 
     protected void reportTooManyCollisions()
     {
-        // First: do not fuzz about small symbol tables
-        if (_hashSize <= 512) { // would have spill-over area of 64 entries
+        // First: do not fuzz about small symbol tables; may get balanced by doubling up
+        if (_hashSize <= 1024) { // would have spill-over area of 128 entries
             return;
         }
         throw new IllegalStateException("Spill-over slots in symbol table with "+_count
                 +" entries, hash area of "+_hashSize+" slots is now full (all "
-                +(_hashSize >> 3)+" slots -- suspect a DoS attack based on hash collisions");
+                +(_hashSize >> 3)+" slots -- suspect a DoS attack based on hash collisions."
+                +" You can disable the check via `JsonFactory.Feature.FAIL_ON_SYMBOL_HASH_OVERFLOW`");
     }
 
     static int _calcTertiaryShift(int primarySlots)
@@ -1204,7 +1205,7 @@ static int _calcTertiaryShift(int primarySlots)
         if (tertSlots <= 256) { // buckets of 8 slots (up to 256 == 32 x 8)
             return 5;
         }
-        if (tertSlots <= 2048) { // buckets of 16 slots (up to 1024 == 64 x 16)
+        if (tertSlots <= 1024) { // buckets of 16 slots (up to 1024 == 64 x 16)
             return 6;
         }
         // and biggest buckets have 32 slots

src/test/java/com/fasterxml/jackson/core/sym/TestSymbolTables.java

@@ -79,11 +79,11 @@ public void testSyntheticWithBytesNew() throws IOException
 
         // fragile, but essential to verify low collision counts;
         // anywhere between 70-80% primary matches
-        assertEquals(8515, symbols.primaryCount());
+        assertEquals(8524, symbols.primaryCount());
         // secondary between 10-20%
-        assertEquals(2525, symbols.secondaryCount());
+        assertEquals(2534, symbols.secondaryCount());
         // and most of remaining in tertiary
-        assertEquals(960, symbols.tertiaryCount());
+        assertEquals(942, symbols.tertiaryCount());
         // so that spill-over is empty or close to
         assertEquals(0, symbols.spilloverCount());
     }

src/test/java/com/fasterxml/jackson/core/sym/TestSymbolsWithMediaItem.java

@@ -1,7 +1,6 @@
 package com.fasterxml.jackson.core.sym;
 
 import java.io.IOException;
-import java.nio.charset.Charset;
 
 import com.fasterxml.jackson.core.*;