On Tue, 19 Sep 2023 09:03:35 GMT, 温绍锦 <d...@openjdk.org> wrote:
>> In the improvement of @cl4es PR #15591, the advantages of non-lookup-table >> were discussed. >> >> But if the input is byte[], using lookup table can improve performance. >> >> For HexFormat#formatHex(Appendable, byte[]) and HexFormat#formatHex(byte[]), >> If the length of byte[] is larger, the performance of table lookup will be >> improved more obviously. > > 温绍锦 has updated the pull request incrementally with one additional commit > since the last revision: > > "-" -> "& ~" src/java.base/share/classes/jdk/internal/util/HexDigits.java line 103: > 101: short v = DIGITS[i & 0xff]; > 102: return ucase > 103: ? (short) (v - ((v & 0b0100_0000_0100_0000) >> 1)) // > really: v - ((v >= 'a' && v <= 'f') ? 32 : 0) I think this logic is somewhat complicated that explaining directly is better: `0b0100_0000_0100_0000` is a selector that selects letters (1 << 6), uppercase or not, and shifting it right by 1 bit incidentally becomes a bit offset between cases (1 << 5). I think you can keep the original `& ~` which is clearer (as `-` will not work had the differences not be aligned bit-wise). But you should explain what `>> 1` does which is a major hurdle to understanding this function. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/15768#discussion_r1329835145
