RFR: 8347009: Speed ​​up parseInt and parseLong [v15]

[Raffaello Giulietti]

On Wed, 5 Feb 2025 00:19:31 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:
> 
>   fix JdbExprTest

src/java.base/share/classes/jdk/internal/util/DecimalDigits.java line 143:

> 141:      * @return If both characters are numbers, return d0 * 10 + d1, otherwise return -1
> 142:      */
> 143:     @ForceInline

Can we leave this out? From the doc: "This annotation must be used sparingly."
I tried without and on M1 performance does not seem to be affected.

src/java.base/share/classes/jdk/internal/util/DecimalDigits.java line 175:

> 173:          */
> 174:         int d;
> 175:         short x = UNSAFE.getShortUnaligned(str, Unsafe.ARRAY_BYTE_BASE_OFFSET + offset, false);

@wenshao I'm a bit worried about the use of Unsafe here.

This method is `public` (although in an internal package), and while it is used correctly in this PR, there's no warning in the doc that `str` and `offset` must come from a trusted caller that ensures that they are safe to use with, well..., Unsafe.

Did you consider safer alternatives, like usage of `VarHandle`, even if that might mean a slight performance degradation?

test/jdk/com/sun/jdi/JdbExprTest.java line 115:

> 113:                 .shouldMatch("InvalidTypeException: .* convert 2147483648 to int");
> 114:         execCommand(JdbCommand.set("JdbExprTestTarg.anInt", "0x8000000000000000L"))
> 115:                 .shouldContain("java.lang.NumberFormatException: Error at index 15 in: \"8000000000000000\"");

Copyright year should be adjusted.

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PR Review Comment: https://git.openjdk.org/jdk/pull/22919#discussion_r1942751206
PR Review Comment: https://git.openjdk.org/jdk/pull/22919#discussion_r1942775434
PR Review Comment: https://git.openjdk.org/jdk/pull/22919#discussion_r1942778070