Hi Vladimir,
On 24/07/2019 8:53 pm, Vladimir Yaroslavskiy wrote:
Hi all,
I've found bug in parallel sorting of float / double arrays in the latest JDK.
When float / double values are sorted, additional actions are
required: NaNs must be moved to the end and negative zeros
must be placed before positive zeros.
Current implementation of Arrays.parallelSort(float[] / double [])
invokes parallel merge sort from ArraysParallelSortHelpers class,
but it doesn't arrange NaNs and -0.0.
It ultimately uses DualPivotQuicksort which AFAICS does have code to
arrange NaNS:
static void sort(float[] a, int left, int right,
float[] work, int workBase, int workLen) {
/*
* Phase 1: Move NaNs to the end of the array.
*/
while (left <= right && Float.isNaN(a[right])) {
--right;
}
and also order +/-0
/*
* Phase 3: Place negative zeros before positive zeros.
*/
where does the bug arise?
Thanks,
David
-----
@Alan, Brent, Laurent
Could you please file a bug?
New optimized version of DualPivotQuicksort (which is under review) works fine
and
doesn't contain this bug. Please, look at my test case to reproduce it.
----------------------------------------------------------------------------------------------------------------------
import java.util.Random;
public class FailedFloat {
private static final int MAX_N = (1 << 13) /* Arrays.MIN_ARRAY_SORT_GRAN
*/ + 10;
public static void main(String[] args) {
float[] a = new float[MAX_N];
random(a);
java.util.Arrays.parallelSort(a);
check(a);
System.out.println("PASSED");
}
private static void random(float[] a) {
Random random = new Random(777);
for (int i = 0; i < MAX_N; i++) {
a[i] = random.nextBoolean() ? -0.0f : 0.0f;
}
}
private static void check(float[] a) {
for (int i = 0; i < a.length - 1; ++i) {
if (Float.floatToRawIntBits(a[i]) == 0 && Float.floatToRawIntBits(a[i
+ 1]) < 0) {
throw new RuntimeException(a[i] + " goes before "+ a[i + 1] + " at
position " + i);
}
}
}
}
------------------------------------------------------------------------------------------------------------------------
Thank you,
Vladimir
