Hi Peter!
On 3/20/18 6:05 AM, Peter Levart wrote:
Hi Ivan,
What about branch-less variant?
public static int highestOneBit(int i) {
return i & (MIN_VALUE >>> numberOfLeadingZeros(i));
}
Nice variant!I tried to run it, but the numbers are non-distinguishable for non-zero arguments.
And my variant performs slightly better with zero argument. So, I think it's reasonable to keep the variant with the ternary operator. Here are the results: Benchmark (arg) Mode Cnt Score Error UnitsMyBenchmark.int_testMethod_00_base 0 thrpt 35 352.509 ± 20.796 ops/us MyBenchmark.int_testMethod_00_base 42 thrpt 35 362.955 ± 7.278 ops/us MyBenchmark.int_testMethod_00_base -42 thrpt 35 366.084 ± 6.770 ops/us MyBenchmark.int_testMethod_01_org 0 thrpt 35 249.340 ± 1.981 ops/us MyBenchmark.int_testMethod_01_org 42 thrpt 35 249.007 ± 2.005 ops/us MyBenchmark.int_testMethod_01_org -42 thrpt 35 241.866 ± 4.759 ops/us MyBenchmark.int_testMethod_02_new 0 thrpt 35 328.389 ± 5.883 ops/us MyBenchmark.int_testMethod_02_new 42 thrpt 35 306.381 ± 5.505 ops/us MyBenchmark.int_testMethod_02_new -42 thrpt 35 300.328 ± 5.644 ops/us MyBenchmark.int_testMethod_03_and 0 thrpt 35 301.559 ± 5.453 ops/us MyBenchmark.int_testMethod_03_and 42 thrpt 35 299.694 ± 5.000 ops/us MyBenchmark.int_testMethod_03_and -42 thrpt 35 301.505 ± 5.664 ops/us
The benchmark updated in place: http://cr.openjdk.java.net/~igerasim/8199843/00/MyBenchmark.java With kind regards Ivan
Would it be any better for call sites that vary 0 and non-0 argument? Regards, Peter On 03/20/2018 09:58 AM, Ivan Gerasimov wrote:Hello!The hightestOneBit function doesn't have an intrinsic and is currently implemented with a dozen of instructions. Alternatively, it could be implemented as MIN_VALUE >>> numberOfLeadingZeros(i), which works for all integers but zero. The former function gets intrisified by hotspot, which results in +27% of throughput (see the jmh results below).Would you please help review this simple fix? BUGURL: https://bugs.openjdk.java.net/browse/JDK-8199843 WEBREV: http://cr.openjdk.java.net/~igerasim/8199843/00/webrev/Benchmark: http://cr.openjdk.java.net/~igerasim/8199843/00/MyBenchmark.javaBenchmark results: Benchmark (arg) Mode Cnt Score Error UnitsMyBenchmark.int_testMethod_new 0 thrpt 35 323430664.593 ± 7492044.171 ops/s MyBenchmark.int_testMethod_new 42 thrpt 35 298526237.078 ± 5978291.689 ops/s MyBenchmark.int_testMethod_new -42 thrpt 35 302903562.073 ± 7984723.721 ops/s MyBenchmark.int_testMethod_org 0 thrpt 35 236245042.891 ± 3635990.596 ops/s MyBenchmark.int_testMethod_org 42 thrpt 35 237903410.753 ± 3437684.390 ops/s MyBenchmark.int_testMethod_org -42 thrpt 35 238472580.618 ± 2654886.010 ops/s MyBenchmark.long_testMethod_new 0 thrpt 35 282646114.501 ± 48028366.305 ops/s MyBenchmark.long_testMethod_new 42 thrpt 35 282382228.405 ± 5781529.307 ops/s MyBenchmark.long_testMethod_new -42 thrpt 35 276724858.286 ± 6529561.227 ops/s MyBenchmark.long_testMethod_org 0 thrpt 35 198500211.972 ± 15096862.367 ops/s MyBenchmark.long_testMethod_org 42 thrpt 35 215854630.194 ± 3112930.563 ops/s MyBenchmark.long_testMethod_org -42 thrpt 35 217992805.521 ± 2622877.082 ops/sThanks in advance!
-- With kind regards, Ivan Gerasimov
