8231174: (fs) FileTime should have 100ns resolution (win)

[Brian Burkhalter]

> On Sep 22, 2019, at 10:37 AM, Alan Bateman <Alan.Bateman at oracle.com> wrote:
> 
>> The value Long.MAX_VALUE nanoseconds represents about 292 years.
>> 
> The Windows time stamps are 64-bit so my concern is that toFileTime will convert from 100ns intervals to nanos and overflow. So I suspect an overflow check is needed there.

I think that this version [1,2] should address the concern.

Thanks,

Brian

[1] diff

--- a/src/java.base/windows/classes/sun/nio/fs/WindowsFileAttributes.java
+++ b/src/java.base/windows/classes/sun/nio/fs/WindowsFileAttributes.java
@@ -139,9 +139,16 @@
     static FileTime toFileTime(long time) {
         // adjust to java epoch retaining 100ns precision
         time += WINDOWS_EPOCH_IN_100NS;
-        // 100ns -> ns
-        time *= 100L;
-        return FileTime.from(time, TimeUnit.NANOSECONDS);
+        try {
+            // 100ns -> ns
+            time = Math.multiplyExact(time, 100L);
+            return FileTime.from(time, TimeUnit.NANOSECONDS);
+        } catch (ArithmeticException e) {
+            // on overflow, fall back to lower precision
+            // 100ns -> us
+            time /= 10L;
+            return FileTime.from(time, TimeUnit.MICROSECONDS);
+        }
     }

[2] http://cr.openjdk.java.net/~bpb/8231174/webrev.02/
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