On Wed, 21 Jun 2023 14:13:34 GMT, Per Minborg <pminb...@openjdk.org> wrote:
>>> > Another thing to try is moving fastUUID out of Long - moving to an array >>> > of precomputed hex values means it is not tied to Long internals anymore. >>> >>> A note about `@Stable`: `Integer.digits` and `HEX256` are not, and they >>> might see performance improvements and change the benchmark results if they >>> are declared so. >> >> use HEX256 optimize Integer.toHexString >> https://github.com/wenshao/jdk_8310502_test/blob/main/src/main/java/com/alibaba/openjdk/HexUtils.java >> >> char[] hex256 = UUIDUtils.HEX256; >> >> int i0 = (i >> 24) & 255; >> int i1 = (i >> 16) & 255; >> int i2 = (i >> 8) & 255; >> int i3 = i & 255; >> >> char c0 = hex256[i0]; >> char c1 = hex256[i1]; >> char c2 = hex256[i2]; >> char c3 = hex256[i3]; >> >> byte[] bytes; >> if (COMPACT_STRINGS) { >> if ((i >> 4) == 0) { >> bytes = new byte[1]; >> bytes[0] = (byte) c3; >> } else if ((i >> 8) == 0) { >> bytes = new byte[2]; >> bytes[0] = (byte) (c3 >> 8); >> bytes[1] = (byte) c3; >> } else if ((i >> 12) == 0) { >> bytes = new byte[3]; >> bytes[0] = (byte) c2; >> bytes[1] = (byte) (c3 >> 8); >> bytes[2] = (byte) c3; >> } else if ((i >> 16) == 0) { >> bytes = new byte[4]; >> bytes[0] = (byte) (c2 >> 8); >> bytes[1] = (byte) c2; >> bytes[2] = (byte) (c3 >> 8); >> bytes[3] = (byte) c3; >> } else if ((i >> 20) == 0) { >> bytes = new byte[5]; >> bytes[0] = (byte) c1; >> bytes[1] = (byte) (c2 >> 8); >> bytes[2] = (byte) c2; >> bytes[3] = (byte) (c3 >> 8); >> bytes[4] = (byte) c3; >> } else if ((i >> 24) == 0) { >> bytes = new byte[6]; >> bytes[0] = (byte) (c1 >> 8); >> bytes[1] = (byte) c1; >> bytes[2] = (byte) (c2 >> 8); >> bytes[3] = (byte) c2; >> bytes[4] = (byte) (c3 >> 8); >> bytes[5] = (byte) c3; >> } else if ((i >> 28) == 0) { >> bytes = new byte[7]; >> bytes[0] = (byte) c0; >> bytes[1] = (byte) (c1 >> 8); >> bytes[2] = (byte) c1; >> bytes[3] = (byte) (c2 >> 8); >> ... > > Not sure if this can be applied but some months ago, I optimized Bits to use > VarHandles rather than explicitly shifting bits around. This gave us a > significant performance increase: > > https://github.com/openjdk/jdk/pull/11840/files The key to the optimization was MethodHandles.byteArrayViewVarHandle. Don't know if StringUTF16.putChar and StringUTF16.getChar can benefit from such an update. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/14578#discussion_r1237109343
