Based on some playing around with unrolling loops as part of the crc64
implementation, I tried unrolling the "legacy" implementation and
found it provided some nice improvements. The improvements were most
pronounced on 32 bit jdk 11:
32 jdk 11 - LEGACY
Benchmark (file) Mode Cnt Score
Error Units
XZCompressionBenchmark.compress ihe_ovly_pr.dcm avgt 3 17.812
± 0.588 ms/op
XZCompressionBenchmark.compress image1.dcm avgt 3 8404.259
± 391.678 ms/op
XZCompressionBenchmark.compress large.xml avgt 3 16037.416
± 467.379 ms/op
Unrolled
Benchmark (file) Mode Cnt Score
Error Units
XZCompressionBenchmark.compress ihe_ovly_pr.dcm avgt 3 13.624
± 0.845 ms/op
XZCompressionBenchmark.compress image1.dcm avgt 3 7833.118
± 28.132 ms/op
XZCompressionBenchmark.compress large.xml avgt 3 12838.831
± 192.884 ms/op
32 jdk 11 - LEGACY (server)
Benchmark (file) Mode Cnt Score
Error Units
XZCompressionBenchmark.compress ihe_ovly_pr.dcm avgt 3 14.105
± 0.081 ms/op
XZCompressionBenchmark.compress image1.dcm avgt 3 8474.630
± 518.903 ms/op
XZCompressionBenchmark.compress large.xml avgt 3 16009.553
± 529.315 ms/op
Unrolled
Benchmark (file) Mode Cnt Score
Error Units
XZCompressionBenchmark.compress ihe_ovly_pr.dcm avgt 3 10.513
± 0.290 ms/op
XZCompressionBenchmark.compress image1.dcm avgt 3 7900.578
± 309.317 ms/op
XZCompressionBenchmark.compress large.xml avgt 3 12871.200
± 570.491 ms/op
/**
* Simply loops over all of the bytes, comparing one at a time.
*/
@SuppressWarnings("unused")
private static int legacyMismatch(
byte[] a, int aFromIndex, int bFromIndex, int length) {
int i=0;
for (int j=length - 7; i<j; i+=8) {
if (a[aFromIndex + i] != a[bFromIndex + i])
return i;
if (a[aFromIndex + i + 1] != a[bFromIndex + i + 1])
return i + 1;
if (a[aFromIndex + i + 2] != a[bFromIndex + i + 2])
return i + 2;
if (a[aFromIndex + i + 3] != a[bFromIndex + i + 3])
return i + 3;
if (a[aFromIndex + i + 4] != a[bFromIndex + i + 4])
return i + 4;
if (a[aFromIndex + i + 5] != a[bFromIndex + i + 5])
return i + 5;
if (a[aFromIndex + i + 6] != a[bFromIndex + i + 6])
return i + 6;
if (a[aFromIndex + i + 7] != a[bFromIndex + i + 7])
return i + 7;
}
for ( ; i<length; ++i) {
if (a[aFromIndex + i] != a[bFromIndex + i]) {
return i;
}
}
return length;
}
