Simplify and optimize quad to hex conversion

Author: felixbarny

server/src/main/java/org/elasticsearch/common/network/InetAddresses.java

@@ -126,26 +126,20 @@ private static byte[] convertDottedQuadToHex(byte[] ipUtf8, int offset, int leng
         if (quad == null) {
             return null;
         }
-        byte[] penultimate = toHexBytes(((quad[0] & 0xff) << 8) | (quad[1] & 0xff));
-        byte[] ultimate = toHexBytes(((quad[2] & 0xff) << 8) | (quad[3] & 0xff));
-        // initialPart + penultimate + ":" + ultimate
-        byte[] result = new byte[quadOffset + penultimate.length + 1 + ultimate.length];
+        // initialPart(quadOffset) + penultimate(4) + ":"(1) + ultimate(4)
+        byte[] result = new byte[quadOffset + 9];
         System.arraycopy(ipUtf8, offset, result, 0, quadOffset);
-        System.arraycopy(penultimate, 0, result, quadOffset, penultimate.length);
-        result[quadOffset + penultimate.length] = ':';
-        System.arraycopy(ultimate, 0, result, quadOffset + penultimate.length + 1, ultimate.length);
+        appendHexBytes(result, quadOffset, quad[0], quad[1]); // penultimate part
+        result[quadOffset + 4] = ':';
+        appendHexBytes(result, quadOffset + 5, quad[2], quad[3]); // ultimate part
         return result;
     }
 
-    static byte[] toHexBytes(int val) {
-        int mag = Integer.SIZE - Integer.numberOfLeadingZeros(val);
-        int length = Math.max(((mag + 3) / 4), 1);
-        byte[] result = new byte[length];
-        for (int i = length - 1; i >= 0; i--) {
-            result[i] = (byte) HEX_DIGITS[val & 0xf];
-            val >>>= 4;
-        }
-        return result;
+    static void appendHexBytes(byte[] result, int offset, byte b1, byte b2) {
+        result[offset] = (byte) HEX_DIGITS[((b1 & 0xf0) >> 4)];
+        result[offset + 1] = (byte) HEX_DIGITS[(b1 & 0x0f)];
+        result[offset + 2] = (byte) HEX_DIGITS[((b2 & 0xf0) >> 4)];
+        result[offset + 3] = (byte) HEX_DIGITS[(b2 & 0x0f)];
     }
 
     private static byte[] textToNumericFormatV4(byte[] ipUtf8, int offset, int length, boolean asIpv6) {

server/src/test/java/org/elasticsearch/common/network/InetAddressesTests.java

@@ -25,6 +25,7 @@
 import java.net.InetAddress;
 import java.net.NetworkInterface;
 import java.net.UnknownHostException;
+import java.nio.ByteBuffer;
 import java.nio.charset.StandardCharsets;
 import java.util.Enumeration;
 import java.util.stream.IntStream;
@@ -261,10 +262,16 @@ public void testEncodeAsIpv6() throws Exception {
         );
     }
 
-    public void testToHexBytes() {
-        IntStream.generate(ESTestCase::randomInt).limit(256).forEach(i -> {
-            byte[] bytes = InetAddresses.toHexBytes(i);
-            assertArrayEquals(Integer.toHexString(i).getBytes(StandardCharsets.US_ASCII), bytes);
-        });
+    public void testAppendHexBytes() {
+        for (int i = 0; i < 256; i++) {
+            byte b1 = randomByte();
+            byte b2 = randomByte();
+            // The expected string is the hex representation of the two bytes, padded to 4 characters
+            String expected = String.format("%1$04x", (b1 & 0xFF) << 8 | b2 & 0xFF);
+            byte[] hex = new byte[4];
+            InetAddresses.appendHexBytes(hex, 0, b1, b2);
+            String actual = new String(hex, StandardCharsets.US_ASCII);
+            assertEquals(expected, actual);
+        }
     }
 }