On Mon, 7 Oct 2024 19:48:20 GMT, fabioromano1 <d...@openjdk.org> wrote:
>> `BigDecimal` was not designed to do astronomical computations. One would >> probably use other libraries for that, e.g., [GMP](https://gmplib.org/) and >> would not be interested too much in "stripping trailing zeros". >> The focus of this class is mainly commercial applications, where decimal >> arithmetic is sometimes mandated by regulators. >> >> So I'd expect that most usages, for example SQL or commercial application >> workloads, will process numbers with a few dozens of digits, maybe sometimes >> some hundreds digits for intermediate results. So I think that accelerating >> for these sizes makes the most practical sense. >> >> With modest memory and CPU costs, I think even one million digits or so >> might be processed reasonably fast. >> My point is that there's room for improvement in these range of sizes, but >> perhaps not for larger ones. >> >> More importantly, though, I'd like to avoid one single computation to affect >> the resident memory footprint of a JVM instance for its entire lifetime. > > @rgiulietti FYI, I have found that `BigInteger` has already a cache for the > repeated squares that uses in radix string conversion, and it is provided by > the method `BigInteger.getRadixConversionCache(int radix, int exponent)`. > Although, I don't know if it would be a good idea to use it, because it > computes all the squares up to `radix^(2^exponent)`, and this may not be > necessary but could cost a lot of running time and memory if the number to > strip is very large... Seems like `BigInteger`s division either takes care of removing common powers of 2 in the dividend and divisor (Knuth division), or removing them has no practical benefit (Burnikel-Ziegler). Thus, I'm wondering if using powers of 10 rather than powers of 5 in the stripping logic could simplify the code while retaining comparable performance. The powers of 10 are already indirectly kept in the class by method `bigTenToThe()` (although they affect resident memory footprint). However, since that method is there to stay and used in other places as well, it might be worthwhile to profit from it. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/21323#discussion_r1793603310
