[GitHub] [groovy] danielsun1106 commented on a change in pull request #903: GROOVY-9060: Make the initial capacity of LinkedHashMap be power of 2…

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danielsun1106 commented on a change in pull request #903: GROOVY-9060: Make the initial capacity of LinkedHashMap be power of 2…
URL: https://github.com/apache/groovy/pull/903#discussion_r270651854
 
 

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 File path: src/main/java/org/codehaus/groovy/runtime/InvokerHelper.java
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 @@ -396,10 +402,33 @@ public static List createList(Object[] values) {
         return answer;
     }
 
+    /**
+     * Get the initial capacity of hash map, which is the closest power of 2 to the entry count.
+     * (SEE https://stackoverflow.com/questions/8352378/why-does-hashmap-require-that-the-initial-capacity-be-a-power-of-two)
+     *
+     * e.g.
+     * 1: 1
+     * 2: 2
+     * 3: 4
+     * 4: 4
+     * 5: 8
+     * 6: 8
+     * 7: 8
+     * 8: 8
+     * 9: 16
+     * ...
+     *
+     * @param initialEntryCnt the initial entry count
+     * @return the initial capacity
+     */
+    public static int initialCapacity(int initialEntryCnt) {
+        return (int) pow(2, ceil(log(initialEntryCnt) / LN2));
 
 Review comment:
   `2<<Integer.highestOneBit​(initialEntryCnt)+1; ` increases its result too fast, e.g. 
   When `initialEntryCnt` is 16, the result has already been 262144 😲
   
   Thanks for your suggestion all the same.
   

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