RFR JDK-6321472: Add CRC-32C API

Vitaly Davidovich vitalyd at gmail.com
Fri Oct 17 13:06:29 UTC 2014

In my experiments, ByteBuffer.wrap() with immediate use (e.g. BB.wrap
(...).getInt (...)) does not trigger escape analysis (I.e. the BB is not
eliminated).  I suspect it's because wrap () is not trivial enough and
compiler doesn't "see through" the noise there.

Sent from my phone
On Oct 17, 2014 4:46 AM, "Peter Levart" <peter.levart at gmail.com> wrote:

> On 10/17/2014 03:42 AM, Staffan Friberg wrote:
>> Hi,
>> This RFE adds a CRC-32C class. It implements Checksum so it will have the
>> same API CRC-32, but use a different polynomial when calculating the CRC
>> checksum.
>> CRC-32C implementation uses slicing-by-8 to achieve high performance when
>> calculating the CRC value.
>> A part from adding the new class, java.util.zip.CRC32C, I have also added
>> two default methods to Checksum. These are methods that were added to
>> Adler32 and CRC32 in JDK 8 but before default methods were added, which was
>> why they were only added to the implementors and not the interface.
>> Bug: https://bugs.openjdk.java.net/browse/JDK-6321472
>> Webrev: http://cr.openjdk.java.net/~sfriberg/JDK-6321472/webrev.00
>> I have started a CCC request for the changes, but was asked to get
>> feedback from the core libs group before finalizing the request in case
>> there are any API or Javadoc changes suggested.
>> Thanks,
>> Staffan
> Hi Staffan,
> I can see CRC32C.reflect(int) method reverses the bits in 32 bit int
> value. You could use Integer.reverse(int) instead.
> The CRC32C.swap32(int) method is (almost) exactly the same as
> Integer.reverseBytes(int) and equivalent.
> I wonder if handling ByteBuffer could be simplified. You could leverage
> it's own byte order manipulation by temporarily setting (and resetting
> afterwards) ByteBuffer.order() and then use ByteBuffer.getInt() to extract
> 32 bits at a time for your algorithm. This could get you the optimal
> variant of algorithm for both kinds of buffers (direct or byte[] based).
> Perhaps even the byte[] based variant of algorithm could be implemented by
> wrapping the array with ByteBuffer, passing it to common private method,
> and relying on the escape analysis of Hotspot to allocate the
> HeapByteBuffer wrapper object on stack.
> Regards, Peter

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