On Tue, 29 Apr 2025 20:33:29 GMT, fabioromano1 <d...@openjdk.org> wrote:
>> This PR optimizes `BigInteger.pow(int)` method. The primary enhancement in
>> `pow()` is not concerned most on execution time, but rather in memory
>> optimization, because the PR implementation does the "shift of the exponent"
>> squaring the result rather than the base, so the base is not squared like in
>> the current implementation, and this permits to save about half of the
>> memory.
>
> 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;
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/24690#discussion_r2068549452
