On Wed, 30 Apr 2025 12:20:39 GMT, Raffaello Giulietti <rgiulie...@openjdk.org>
wrote:
>> fabioromano1 has updated the pull request incrementally with one additional
>> commit since the last revision:
>>
>> Simplified the formula for detecting overflows
>
> src/java.base/share/classes/java/math/BigInteger.java line 2737:
>
>> 2735: }
>> 2736:
>> 2737: return pow;
>
> Is there a reason this cannot simply be the traditional "repeated square"
> method?
> Why this complexity?
>
> Suggestion:
>
> if (x == 1L)
> return 1L;
>
> if (x == 2L)
> return 1L << n;
>
> /*
> * The method assumption means that n <= 40 here.
> * Thus, the loop body executes at most 5 times.
> */
> long pow = 1;
> for (; n > 1; x *= x, n >>>= 1) {
> if ((n & 0b1) != 0) {
> pow *= x;
> }
> }
> return pow * x;
@rgiulietti Probably the `powerCache` array is needless because the number of
iterations is very low. Perhaps using `Math.pow(int, int)` could be a faster
way to get the powers, since it reduces the number of iterations further and it
has constant time, although even the traditional "repeated square" method has
constant time...
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/24690#discussion_r2068708270
