On Wed, 11 Oct 2023 09:48:58 GMT, Claes Redestad <redes...@openjdk.org> wrote:
>> Shaojin Wen has updated the pull request incrementally with one additional >> commit since the last revision: >> >> refactor based on @liach 's review > > src/java.base/share/classes/java/math/BigDecimal.java line 4168: > >> 4166: int lowInt = (int)intCompact % 100; >> 4167: int highInt = (int)intCompact / 100; >> 4168: int highIntSize = JLA.stringSize(highInt); > > Which micros cover performance of this branch? > > What performance would you get if you simplified this to, say, `return > highInt + (lowInt < 10 ? ".0" : ".") + lowInt;`? > > `lowInt` is currently unused since you use `(int) intCompact - highInt * 100` > instead below. (While a clever optimization in theory, I believe the JIT > should handle a pair of integer modulo and division operations (`a = intValue > % 100; b = intValue / 100`) so that it only has to do one division, so please > measure that whatever you do here has a significant benefit). Performance numbers run on MacBook M1 Max: -Benchmark Mode Cnt Score Error Units -BigDecimals.testHugeToEngineeringString avgt 15 217.619 ? 4.617 ns/op -BigDecimals.testLargeToEngineeringString avgt 15 65.183 ? 4.368 ns/op -BigDecimals.testSmallToEngineeringString avgt 15 17.084 ? 0.056 ns/op -BigDecimals.testToEngineeringString avgt 15 1856.849 ? 63.571 ns/op +Benchmark Mode Cnt Score Error Units (eec631c) +BigDecimals.testHugeToEngineeringString avgt 15 164.910 ? 1.514 ns/op (+31.97) +BigDecimals.testLargeToEngineeringString avgt 15 20.826 ? 0.066 ns/op (+212.99) +BigDecimals.testSmallToEngineeringString avgt 15 11.987 ? 0.080 ns/op (+42.53) +BigDecimals.testToEngineeringString avgt 15 1854.372 ? 63.810 ns/op (+0.14) The microben covered by fast-path is BigDecimals.testSmallToEngineeringString, highInt + (lowInt < 10 ? ".0" : ".") + lowInt is actually implemented based on StringBuilder and will be much slower than the current baseline. Benchmark Mode Cnt Score Error Units (use StringConcat) BigDecimals.testSmallToEngineeringString avgt 15 41.876 ? 0.182 ns/op ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/16006#discussion_r1355833197
