RFR(S): 8205194: Improve the Array Comparison when there is a mismatch at first element.

[Paul Sandoz]

Hi Vivek,

Thanks for investigating this.

 164     public static int mismatch(boolean[] a,
 165                                boolean[] b,
 166                                int length) {
 167         int i = 0;
 168         if (a[i] != b[i])
 169             return i;
You might as well replace the use if i with 0 and i think you can move this to be performed when the length is greater than the threshold, that way you don’t impact small arrays below the threshold.

 186     public static int mismatch(boolean[] a, int aFromIndex,
 187                                boolean[] b, int bFromIndex,
 188                                int length) {
 189         int i = 0;
 190         if (a[i] != b[i])
 191             return i;
This is incorrect. You need to use aFromIndex and bFromIndex.

Do you run the test test/jdk/java/util/Arrays/ArraysEqCmpTest.java? If that passed then we need to strengthen for the case of a mismatch on the first relative element in each array.

Paul.

> On Jun 19, 2018, at 9:36 AM, Deshpande, Vivek R <vivek.r.deshpande at intel.com> wrote:
> 
> Thanks David.
> Sending it to core-libs-dev.
> 
> I would like to contribute a patch which improves the array comparison when there is a mismatch for the first element.
> This avoids call to vectorizedMismatch method and gives ~80x speed up.
> Could you please review and sponsor the patch.
> Link to bug:
> https://bugs.openjdk.java.net/browse/JDK-8205194
> webrev:
> http://cr.openjdk.java.net/~vdeshpande/vectorizedMismatch_jdk/webrev.00/
> 
> Regards,
> Vivek
> 
> -----Original Message-----
> From: David Holmes [mailto:david.holmes at oracle.com] 
> Sent: Monday, June 18, 2018 10:32 PM
> To: Deshpande, Vivek R <vivek.r.deshpande at intel.com>; jdk-dev at openjdk.java.net
> Subject: Re: RFR(S): 8205194: Improve the Array Comparison when there is a mismatch at first element.
> 
> Hi Vivek,
> 
> Reviews should take place on the appropriate mailing list for the code being changed, not on the jdk-dev list. Please takes this to core-libs-dev.
> 
> Thanks,
> David
> 
> On 19/06/2018 9:52 AM, Deshpande, Vivek R wrote:
>> Hi All
>> 
>> Forgot to add the links:
>> https://bugs.openjdk.java.net/browse/JDK-8205194
>> webrev:
>> http://cr.openjdk.java.net/~vdeshpande/vectorizedMismatch_jdk/webrev.0
>> 0/
>> 
>> Regards.
>> Vivek
>> 
>> From: Deshpande, Vivek R
>> Sent: Monday, June 18, 2018 4:50 PM
>> To: 'jdk-dev at openjdk.java.net' <jdk-dev at openjdk.java.net>
>> Cc: 'Paul Sandoz' <paul.sandoz at oracle.com>; Viswanathan, Sandhya 
>> <sandhya.viswanathan at intel.com>
>> Subject: RFR(S): 8205194: Improve the Array Comparison when there is a mismatch at first element.
>> 
>> Hi All
>> 
>> I would like to contribute a patch which improves the array comparison when there is a mismatch for the first element.
>> This avoids call to vectorizedMismatch method and gives ~80x speed up.
>> Please review and sponsor the patch.
>> 
>> Regards,
>> Vivek
>>