minor optimization for case-insensitive enum lookup

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/databind/deser/std/EnumDeserializer.java

@@ -211,10 +211,9 @@ private final Object _deserializeAltString(JsonParser p, DeserializationContext
             if ((_caseInsensitive == Boolean.TRUE) ||
                     ((_caseInsensitive == null) &&
                             ctxt.isEnabled(DeserializationFeature.READ_ENUMS_IGNORING_CASE))) {
-                for (String key : lookup.keys()) {
-                    if (key.equalsIgnoreCase(name)) {
-                        return lookup.find(key);
-                    }
+                Object match = lookup.findCaseInsensitive(name);
+                if (match != null) {
+                    return match;
                 }
             } else if (!ctxt.isEnabled(DeserializationFeature.FAIL_ON_NUMBERS_FOR_ENUMS)) {
                 // [databind#149]: Allow use of 'String' indexes as well -- unless prohibited (as per above)

src/main/java/com/fasterxml/jackson/databind/util/CompactStringObjectMap.java

@@ -124,6 +124,22 @@ private final Object _find2(String key, int slot, Object match)
         return null;
     }
 
+    /**
+     * @since 2.9
+     */
+    public Object findCaseInsensitive(String key) {
+        for (int i = 0, end = _hashArea.length; i < end; i += 2) {
+            Object k2 = _hashArea[i];
+            if (k2 != null) {
+                String s = (String) k2;
+                if (s.equalsIgnoreCase(key)) {
+                    return _hashArea[i+1];
+                }
+            }
+        }
+        return null;
+    }
+    
     public List<String> keys() {
         final int end = _hashArea.length;
         List<String> keys = new ArrayList<String>(end >> 2);

src/test/java/com/fasterxml/jackson/databind/deser/jdk/EnumAltIdTest.java

@@ -87,7 +87,7 @@ public void testEnumDesIgnoringCaseWithUpperCaseToString() throws IOException {
 
     public void testIgnoreCaseInEnumList() throws Exception {
         TestEnum[] enums = READER_IGNORE_CASE.forType(TestEnum[].class)
-            .readValue("[\"jackson\", \"rules\"]");
+            .readValue("[\"jacksON\", \"ruLes\"]");
 
         assertEquals(2, enums.length);
         assertEquals(TestEnum.JACKSON, enums[0]);