8310502: Optimization for j.l.Long.fastUUID()

Reviewed-by: liach, alanb

src/java.base/share/classes/java/lang/Long.java

@@ -445,39 +445,6 @@ public final class Long extends Number
         } while (charPos > offset);
     }
 
-    static String fastUUID(long lsb, long msb) {
-        if (COMPACT_STRINGS) {
-            byte[] buf = new byte[36];
-            formatUnsignedLong0(lsb,        4, buf, 24, 12);
-            formatUnsignedLong0(lsb >>> 48, 4, buf, 19, 4);
-            formatUnsignedLong0(msb,        4, buf, 14, 4);
-            formatUnsignedLong0(msb >>> 16, 4, buf, 9,  4);
-            formatUnsignedLong0(msb >>> 32, 4, buf, 0,  8);
-
-            buf[23] = '-';
-            buf[18] = '-';
-            buf[13] = '-';
-            buf[8]  = '-';
-
-            return new String(buf, LATIN1);
-        } else {
-            byte[] buf = new byte[72];
-
-            formatUnsignedLong0UTF16(lsb,        4, buf, 24, 12);
-            formatUnsignedLong0UTF16(lsb >>> 48, 4, buf, 19, 4);
-            formatUnsignedLong0UTF16(msb,        4, buf, 14, 4);
-            formatUnsignedLong0UTF16(msb >>> 16, 4, buf, 9,  4);
-            formatUnsignedLong0UTF16(msb >>> 32, 4, buf, 0,  8);
-
-            StringUTF16.putChar(buf, 23, '-');
-            StringUTF16.putChar(buf, 18, '-');
-            StringUTF16.putChar(buf, 13, '-');
-            StringUTF16.putChar(buf,  8, '-');
-
-            return new String(buf, UTF16);
-        }
-    }
-
     /**
      * Returns a {@code String} object representing the specified
      * {@code long}.  The argument is converted to signed decimal

src/java.base/share/classes/java/lang/System.java

@@ -2395,9 +2395,6 @@ public final class System {
             public Package definePackage(ClassLoader cl, String name, Module module) {
                 return cl.definePackage(name, module);
             }
-            public String fastUUID(long lsb, long msb) {
-                return Long.fastUUID(lsb, msb);
-            }
             @SuppressWarnings("removal")
             public void addNonExportedPackages(ModuleLayer layer) {
                 SecurityManager.addNonExportedPackages(layer);

src/java.base/share/classes/java/util/HexDigits.java

@@ -35,6 +35,44 @@ import jdk.internal.vm.annotation.Stable;
  * @since 21
  */
 final class HexDigits implements Digits {
+    /**
+     * Each element of the array represents the ascii encoded
+     * hex relative to its index, for example:<p>
+     * <pre>
+     *       0 -> '00' -> ('0' << 8) | '0' -> 12336
+     *       1 -> '01' -> ('0' << 8) | '1' -> 12337
+     *       2 -> '02' -> ('0' << 8) | '2' -> 12338
+     *
+     *     ...
+     *
+     *      10 -> '0a' -> ('0' << 8) | 'a' -> 12385
+     *      11 -> '0b' -> ('0' << 8) | 'b' -> 12386
+     *      12 -> '0c' -> ('0' << 8) | 'b' -> 12387
+     *
+     *     ...
+     *
+     *      26 -> '1a' -> ('1' << 8) | 'a' -> 12641
+     *      27 -> '1b' -> ('1' << 8) | 'b' -> 12642
+     *      28 -> '1c' -> ('1' << 8) | 'c' -> 12643
+     *
+     *     ...
+     *
+     *     253 -> 'fd' -> ('f' << 8) | 'd' -> 26212
+     *     254 -> 'fe' -> ('f' << 8) | 'e' -> 26213
+     *     255 -> 'ff' -> ('f' << 8) | 'f' -> 26214
+     * </pre>
+     * <p>use like this:
+     * <pre>
+     *     int v = 254;
+     *
+     *     char[] chars = new char[2];
+     *
+     *     short i = DIGITS[v]; // 26213
+     *
+     *     chars[0] = (char) (byte) (i >> 8); // 'f'
+     *     chars[1] = (char) (byte) i;        // 'e'
+     * </pre>
+     */
     @Stable
     private static final short[] DIGITS;
 
@@ -64,6 +102,23 @@ final class HexDigits implements Digits {
     private HexDigits() {
     }
 
+    /**
+     * Combine two hex shorts into one int based on big endian
+     */
+    static int digit(int b0, int b1) {
+        return (DIGITS[b0 & 0xff] << 16) | DIGITS[b1 & 0xff];
+    }
+
+    /**
+     * Combine four hex shorts into one long based on big endian
+     */
+    static long digit(int b0, int b1, int b2, int b3) {
+        return (((long) DIGITS[b0 & 0xff]) << 48)
+                | (((long) DIGITS[b1 & 0xff]) << 32)
+                | (DIGITS[b2 & 0xff] << 16)
+                | DIGITS[b3 & 0xff];
+    }
+
     @Override
     public int digits(long value, byte[] buffer, int index,
                       MethodHandle putCharMH) throws Throwable {

src/java.base/share/classes/java/util/UUID.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2003, 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2003, 2023, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -25,10 +25,13 @@
 
 package java.util;
 
+import java.nio.charset.CharacterCodingException;
+import java.nio.charset.StandardCharsets;
 import java.security.*;
 
 import jdk.internal.access.JavaLangAccess;
 import jdk.internal.access.SharedSecrets;
+import jdk.internal.util.ByteArray;
 
 /**
  * A class that represents an immutable universally unique identifier (UUID).
@@ -463,7 +466,43 @@ public final class UUID implements java.io.Serializable, Comparable<UUID> {
      */
     @Override
     public String toString() {
-        return jla.fastUUID(leastSigBits, mostSigBits);
+        long lsb = leastSigBits;
+        long msb = mostSigBits;
+        byte[] buf = new byte[36];
+        ByteArray.setLong(
+                buf,
+                0,
+                HexDigits.digit((int) (msb >> 56), (int) (msb >> 48), (int) (msb >> 40), (int) (msb >> 32)));
+        buf[8] = '-';
+        ByteArray.setInt(
+                buf,
+                9,
+                HexDigits.digit(((int) msb) >> 24, ((int) msb) >> 16));
+        buf[13] = '-';
+        ByteArray.setInt(
+                buf,
+                14,
+                HexDigits.digit(((int) msb) >> 8, (int) msb));
+        buf[18] = '-';
+        ByteArray.setInt(
+                buf,
+                19,
+                HexDigits.digit((int) (lsb >> 56), (int) (lsb >> 48)));
+        buf[23] = '-';
+        ByteArray.setLong(
+                buf,
+                24,
+                HexDigits.digit(((int) (lsb >> 40)), (int) (lsb >> 32), ((int) lsb) >> 24, ((int) lsb) >> 16));
+        ByteArray.setInt(
+                buf,
+                32,
+                HexDigits.digit(((int) lsb) >> 8, (int) lsb));
+
+        try {
+            return jla.newStringNoRepl(buf, StandardCharsets.ISO_8859_1);
+        } catch (CharacterCodingException cce) {
+            throw new AssertionError(cce);
+        }
     }
 
     /**

src/java.base/share/classes/jdk/internal/access/JavaLangAccess.java

@@ -176,11 +176,6 @@ public interface JavaLangAccess {
      */
     Package definePackage(ClassLoader cl, String name, Module module);
 
-    /**
-     * Invokes Long.fastUUID
-     */
-    String fastUUID(long lsb, long msb);
-
     /**
      * Record the non-exported packages of the modules in the given layer
      */