RFR: 8347009: Speed ​​up parseInt and parseLong [v11]

[Johannes Graham]

On Wed, 29 Jan 2025 16:30:46 GMT, Shaojin Wen <swen at openjdk.org> wrote:

>> This is an optimization for decimal Integer.parseInt and Long.parseLong, which improves performance by about 10%. The optimization includes:
>> 1. Improve performance by parsing 2 numbers at a time, which has performance improvements for numbers with length >= 3.
>> 2. It uses charAt(0) for the first number. Assuming that the optimization can eliminate boundary checks, this will be more friendly to parsing numbers with length 1.
>> 3. It removes the reliance on the Character.digit method and eliminates the reliance on the CharacterDataLatin1#DIGITS cache array, which avoids performance degradation caused by cache misses.
>
> Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   copyright

src/java.base/share/classes/jdk/internal/util/DecimalDigits.java line 181:

> 179:             return -1;
> 180:         }
> 181:         return ((d & 0xF) << 3) + ((d & 0xF) << 1)  // (d & 0xF) * 10

Is simply using `(d & 0xF) * 10` any worse? I expect the compiler knows this trick and would use it when appropriate.

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PR Review Comment: https://git.openjdk.org/jdk/pull/22919#discussion_r1934408496