RFR JDK-6321472: Add CRC-32C API

[Peter Levart]

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