RFR: 8196331: Optimize Character.digit for latin1 input

[Claes Redestad]

Right, I can't really explain why, but the effect is very visible and
reproducible in microbenchmarks. Differences in generated ASM might
be indicating that the inlining behavior changes enough to shift the
result around; maybe a job for @ForceInline?

I'll experiment and analyze a bit more tomorrow to see if I can find a
good explanation for the observed difference and/or a solution that
allows us to slim down the lookup array.

/Claes

On 2018-01-29 20:38, Paul Sandoz wrote:
> Smaller in only the upper bound? I would an explicit upper bounds 
> check would dominate that of the bounds check for the array itself.
>
> Paul.
>
>> On Jan 29, 2018, at 11:37 AM, Claes Redestad 
>> <claes.redestad at oracle.com <mailto:claes.redestad at oracle.com>> wrote:
>>
>> I ran with a smaller byte[] initially and saw about a 10% improvement 
>> from removing the branch, which is why I felt the superfluous bytes 
>> were motivated.
>>
>> /Claes
>>
>> Paul Sandoz <paul.sandoz at oracle.com <mailto:paul.sandoz at oracle.com>> 
>> skrev: (29 januari 2018 19:14:44 CET)
>>
>>
>>         On Jan 29, 2018, at 9:44 AM, Martin Buchholz
>>         <martinrb at google.com <mailto:martinrb at google.com>> wrote:
>>         Thanks. I might try to shrink the size of the static array,
>>         by only storing values between '0' and 'z', at the cost of
>>         slightly greater lookup costs for each char. 
>>
>>
>>     I was wondering the same, or just clip the end of the array to’z'
>>
>>     if (ch <= ‘z’ && radix …) { // Might even fold the upper bounds check for DIGITS
>>        value = DIGITS[ch];
>>        ...
>>     }
>>
>>     Paul.
>>
>>         On Mon, Jan 29, 2018 at 3:15 AM, Claes Redestad
>>         <claes.redestad at oracle.com
>>         <mailto:claes.redestad at oracle.com>> wrote:
>>
>>             Hi, for the latin1 block of CharacterData we can improve
>>             the digit(int, int) implementation by providing an
>>             optimized lookup table. This improves microbenchmarks
>>             exercising Integer.parseInt, Long.parseLong and
>>             UUID.fromString etc by around 50%for typical inputs.
>>             Webrev:
>>             http://cr.openjdk.java.net/~redestad/8196331/open.00/
>>             <http://cr.openjdk.java.net/%7Eredestad/8196331/open.00/>
>>             Bug: https://bugs.openjdk.java.net/browse/JDK-8196331 The
>>             lookup array is pre-calculated to minimize startup impact
>>             (adds 1,027 bytecodes executed during initialization) /Claes 
>>
>>
>>
>> -- 
>> Sent from my Android device with K-9 Mail. Please excuse my brevity.
>