On Wed, 21 Jun 2023 09:48:54 GMT, 温绍锦 <d...@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. > >> > 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); > bytes[4] = (byte) c2; > bytes[5] = (byte) (c3 >> 8); > bytes[6] = (byte) c3; > ... 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 ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/14578#discussion_r1237075217
