Optimize int and long to string

src/java.base/share/classes/java/lang/StringLatin1.java

@@ -126,11 +126,11 @@ static int getChars(int i, int index, byte[] buf) {
             charPos -= 2;
             writeDigitPair(buf, charPos, -i);
         } else {
-            buf[--charPos] = (byte)('0' - i);
+            putChar(buf, --charPos, '0' - i);
         }
 
         if (negative) {
-            buf[--charPos] = (byte)'-';
+            putChar(buf, --charPos, '-');
         }
         return charPos;
     }
@@ -185,19 +185,19 @@ static int getChars(long i, int index, byte[] buf) {
             charPos -= 2;
             writeDigitPair(buf, charPos, -i2);
         } else {
-            buf[--charPos] = (byte)('0' - i2);
+            putChar(buf, --charPos, '0' - i2);
         }
 
         if (negative) {
-            buf[--charPos] = (byte)'-';
+            putChar(buf, --charPos, '-');
         }
         return charPos;
     }
 
     private static void writeDigitPair(byte[] buf, int charPos, int value) {
         short pair = DecimalDigits.digitPair(value);
-        buf[charPos] = (byte)(pair);
-        buf[charPos + 1] = (byte)(pair >> 8);
+        putChar(buf, charPos    , (byte)(pair));
+        putChar(buf, charPos + 1, (byte)(pair >> 8));
     }
 
     public static void getChars(byte[] value, int srcBegin, int srcEnd, char[] dst, int dstBegin) {
@@ -849,8 +849,8 @@ static void putCharsAt(byte[] val, int index, int c1, int c2, int c3, int c4, in
     }
 
     public static void putChar(byte[] val, int index, int c) {
-        //assert (canEncode(c));
-        val[index] = (byte)(c);
+        assert index >= 0 && index < length(val) : "Trusted caller missed bounds check";
+        UNSAFE.putByte(val, Unsafe.ARRAY_BYTE_BASE_OFFSET + index, (byte) c);
     }
 
     public static char getChar(byte[] val, int index) {

test/micro/org/openjdk/bench/java/lang/StringBuilders.java

@@ -54,6 +54,8 @@ public class StringBuilders {
     private StringBuilder sbLatin2;
     private StringBuilder sbUtf16;
     private StringBuilder sbUtf17;
+    private int[] intsArray;
+    private long[] longArray;
 
     @Setup
     public void setup() {
@@ -69,6 +71,13 @@ public void setup() {
         sbLatin2 = new StringBuilder("Latin1 string");
         sbUtf16 = new StringBuilder("UTF-\uFF11\uFF16 string");
         sbUtf17 = new StringBuilder("UTF-\uFF11\uFF16 string");
+        int size = 16;
+        intsArray = new int[size];
+        longArray = new long[size];
+        for (int i = 0; i < longArray.length; i++) {
+            intsArray[i] = ((100 * i + i) << 24) + 4543 + i * 4;
+            longArray[i] = ((100L * i + i) << 32) + 4543 + i * 4L;
+        }
     }
 
     @Benchmark
@@ -224,6 +233,47 @@ public String toStringCharWithInt8() {
         return result.toString();
     }
 
+    @Benchmark
+    public int appendWithIntLatin1() {
+        StringBuilder buf = sbLatin1;
+        buf.setLength(0);
+        for (long l : longArray) {
+            buf.append(l);
+        }
+        return buf.length();
+    }
+
+    @Benchmark
+    public int appendWithIntUtf16() {
+        StringBuilder buf = sbUtf16;
+        buf.setLength(0);
+        buf.setLength(0);
+        for (long l : longArray) {
+            buf.append(l);
+        }
+        return buf.length();
+    }
+
+    @Benchmark
+    public int appendWithLongLatin1() {
+        StringBuilder buf = sbLatin1;
+        buf.setLength(0);
+        for (long l : longArray) {
+            buf.append(l);
+        }
+        return buf.length();
+    }
+
+    @Benchmark
+    public int appendWithLongUtf16() {
+        StringBuilder buf = sbUtf16;
+        buf.setLength(0);
+        buf.setLength(0);
+        for (long l : longArray) {
+            buf.append(l);
+        }
+        return buf.length();
+    }
 
     @Benchmark
     public int appendWithBool8Latin1() {