8333833: Remove the use of ByteArrayLittleEndian from UUID::toString

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2003, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2003, 2024, 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
@@ -31,7 +31,6 @@
 
 import jdk.internal.access.JavaLangAccess;
 import jdk.internal.access.SharedSecrets;
-import jdk.internal.util.ByteArrayLittleEndian;
 import jdk.internal.util.HexDigits;
 
 /**
@@ -467,38 +466,24 @@ public long node() {
      */
     @Override
     public String toString() {
-        long lsb = leastSigBits;
-        long msb = mostSigBits;
+        int i0 = (int) (mostSigBits >> 32);
+        int i1 = (int) mostSigBits;
+        int i2 = (int) (leastSigBits >> 32);
+        int i3 = (int) leastSigBits;
+
         byte[] buf = new byte[36];
-        ByteArrayLittleEndian.setLong(
-                buf,
-                0,
-                HexDigits.packDigits((int) (msb >> 56), (int) (msb >> 48), (int) (msb >> 40), (int) (msb >> 32)));
+        HexDigits.put4(buf, 0, i0 >> 16);
+        HexDigits.put4(buf, 4, i0);
         buf[8] = '-';
-        ByteArrayLittleEndian.setInt(
-                buf,
-                9,
-                HexDigits.packDigits(((int) msb) >> 24, ((int) msb) >> 16));
+        HexDigits.put4(buf, 9, i1 >> 16);
         buf[13] = '-';
-        ByteArrayLittleEndian.setInt(
-                buf,
-                14,
-                HexDigits.packDigits(((int) msb) >> 8, (int) msb));
+        HexDigits.put4(buf, 14, i1);
         buf[18] = '-';
-        ByteArrayLittleEndian.setInt(
-                buf,
-                19,
-                HexDigits.packDigits((int) (lsb >> 56), (int) (lsb >> 48)));
+        HexDigits.put4(buf, 19, i2 >> 16);
         buf[23] = '-';
-        ByteArrayLittleEndian.setLong(
-                buf,
-                24,
-                HexDigits.packDigits((int) (lsb >> 40), (int) (lsb >> 32), ((int) lsb) >> 24, ((int) lsb) >> 16));
-        ByteArrayLittleEndian.setInt(
-                buf,
-                32,
-                HexDigits.packDigits(((int) lsb) >> 8, (int) lsb));
-
+        HexDigits.put4(buf, 24, i2);
+        HexDigits.put4(buf, 28, i3 >> 16);
+        HexDigits.put4(buf, 32, i3);
         try {
             return jla.newStringNoRepl(buf, StandardCharsets.ISO_8859_1);
         } catch (CharacterCodingException cce) {

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2024, 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
@@ -114,24 +114,19 @@ public static short digitPair(int i, boolean ucase) {
     }
 
     /**
-     * Return a little-endian packed integer for the 4 ASCII bytes for an input unsigned 2-byte integer.
-     * {@code b0} is the most significant byte and {@code b1} is the least significant byte.
-     * The integer is passed byte-wise to allow reordering of execution.
+     * Insert the unsigned 2-byte integer into the buffer as 4 hexadecimal digit ASCII bytes,
+     * only least significant 16 bits of {@code value} are used.
+     * @param buffer byte buffer to copy into
+     * @param index insert point
+     * @param value to convert
      */
-    public static int packDigits(int b0, int b1) {
-        return DIGITS[b0 & 0xff] | (DIGITS[b1 & 0xff] << 16);
-    }
-
-    /**
-     * Return a little-endian packed long for the 8 ASCII bytes for an input unsigned 4-byte integer.
-     * {@code b0} is the most significant byte and {@code b3} is the least significant byte.
-     * The integer is passed byte-wise to allow reordering of execution.
-     */
-    public static long packDigits(int b0, int b1, int b2, int b3) {
-        return DIGITS[b0 & 0xff]
-                | (DIGITS[b1 & 0xff] << 16)
-                | (((long) DIGITS[b2 & 0xff]) << 32)
-                | (((long) DIGITS[b3 & 0xff]) << 48);
+    public static void put4(byte[] buffer, int index, int value) {
+        // Prepare an int value so C2 generates a 4-byte write instead of two 2-byte writes
+        int v = (DIGITS[value & 0xff] << 16) | DIGITS[(value >> 8) & 0xff];
+        buffer[index]     = (byte)  v;
+        buffer[index + 1] = (byte) (v >> 8);
+        buffer[index + 2] = (byte) (v >> 16);
+        buffer[index + 3] = (byte) (v >> 24);
     }
 
     /**