On Fri, 11 Feb 2022 15:04:03 GMT, Roger Riggs <[email protected]> wrote:
>> XenoAmess has refreshed the contents of this pull request, and previous
>> commits have been removed. The incremental views will show differences
>> compared to the previous content of the PR. The pull request contains one
>> new commit since the last revision:
>>
>> 9072610: HashMap.putAll can cause redundant space waste
>
> src/java.base/share/classes/java/util/WeakHashMap.java line 247:
>
>> 245: */
>> 246: private static int calculateHashMapCapacity(int size){
>> 247: return size + (size + 2) / 3;
>
> Consider integer overflow; if size were Integer.MAX_VALUE / 2; the
> computation would overflow.
> The negative result would eventually throw an exception. Using Long for the
> computation would avoid that and keep the expression simple.
@RogerRiggs
Hi. I added a overflow check.
The check makes sure it cannot overflow now.
I wrote a test to show this overflow check be correct.
public class A {
/**
* use for calculate HashMap capacity, using default load factor 0.75
*
* @param size size
* @return HashMap capacity under default load factor
*/
private static int calculateHashMapCapacity(int size) {
if (size > (int) (Integer.MAX_VALUE * 0.75)) {
return Integer.MAX_VALUE;
}
return size + (size + 2) / 3;
}
public static void main(String[] args) {
for (int i = 1; i < Integer.MAX_VALUE ; ++i) {
if (calculateHashMapCapacity(i) <= 0) {
System.err.println(i);
return;
}
}
}
}
I also see the compiled result to make sure the `(int) (Integer.MAX_VALUE *
0.75)` calculation is made at compiling but not runtime, which will not make
this function too much slower.
please review again, thanks!
-------------
PR: https://git.openjdk.java.net/jdk/pull/7431
