RFR: 8196331: Optimize Character.digit for latin1 input

[Claes Redestad]

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> skrev: (29 januari 2018 19:14:44 CET)
>
>
>> On Jan 29, 2018, at 9:44 AM, Martin Buchholz <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>
>> 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/
>>> 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
>>> 

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