On Thu, 31 Aug 2023 19:53:17 GMT, Claes Redestad <redes...@openjdk.org> wrote:
>> 温绍锦 has updated the pull request incrementally with one additional commit
>> since the last revision:
>>
>> assert bounds check
>
> src/java.base/share/classes/java/lang/StringUTF16.java line 1585:
>
>> 1583: buf,
>> 1584: Unsafe.ARRAY_BYTE_BASE_OFFSET + (charPos << 1),
>> 1585: PACKED_DIGITS_UTF16[r]);
>
> What performance would you get if you used the same lookup table as the other
> implementations, but inflate the value to UTF-16 on the fly?
>
>
> int packed = (int)Integer.PACKED_DIGITS[r];
> int inflated = ((packed & 0xFF00) << 8) | (packed & 0xFF));
> UNSAFE.putIntUnaligned(
> buf,
> Unsafe.ARRAY_BYTE_BASE_OFFSET + (charPos << 1),
> inflated);
>
>
> This would avoid juggling more lookup table data around than before,
> alleviating some of the concerns voiced in this PR comment thread.
Good suggestion, using the same lookup table, we can get similar performance.
int packed = (int) Integer.PACKED_DIGITS[-i];
int inflated = ((packed & 0xFF00) << 8) | (packed & 0xFF);
charPos -= 2;
assert charPos >= 0 && charPos < buf.length : "Trusted caller missed bounds
check";
UNSAFE.putIntUnaligned(
buf,
Unsafe.ARRAY_BYTE_BASE_OFFSET + (charPos << 1),
inflated,
false);
The performance comparison data is as follows:
-Benchmark Mode Cnt Score Error Units
-StringBuilders.toStringCharWithInt8UTF16 avgt 15 26.812 ± 0.095 ns/op
+Benchmark Mode Cnt Score Error Units
(use same lookup table)
+StringBuilders.toStringCharWithInt8UTF16 avgt 15 27.807 ± 0.046 ns/op
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/14699#discussion_r1312910616
