Integrate google internal changes.

1 files changed, 1433 insertions, 231 deletions

diff --git a/java/core/src/main/java/com/google/protobuf/Utf8.java b/java/core/src/main/java/com/google/protobuf/Utf8.java
index 48c7e9e6..308c69e9 100644
--- a/java/core/src/main/java/com/google/protobuf/Utf8.java
+++ b/java/core/src/main/java/com/google/protobuf/Utf8.java
@@ -30,6 +30,19 @@
 
 package com.google.protobuf;
 
+import static java.lang.Character.MAX_SURROGATE;
+import static java.lang.Character.MIN_SURROGATE;
+import static java.lang.Character.isSurrogatePair;
+import static java.lang.Character.toCodePoint;
+
+import java.lang.reflect.Field;
+import java.nio.Buffer;
+import java.nio.ByteBuffer;
+import java.security.AccessController;
+import java.security.PrivilegedExceptionAction;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
 /**
  * A set of low-level, high-performance static utility methods related
  * to the UTF-8 character encoding.  This class has no dependencies
@@ -64,9 +77,24 @@ package com.google.protobuf;
  *
  * @author martinrb@google.com (Martin Buchholz)
  */
+// TODO(nathanmittler): Copy changes in this class back to Guava
 final class Utf8 {
-  private Utf8() {}
-  
+  private static final Logger logger = Logger.getLogger(Utf8.class.getName());
+
+  /**
+   * UTF-8 is a runtime hot spot so we attempt to provide heavily optimized implementations
+   * depending on what is available on the platform. The processor is the platform-optimized
+   * delegate for which all methods are delegated directly to.
+   */
+  private static final Processor processor =
+      UnsafeProcessor.isAvailable() ? new UnsafeProcessor() : new SafeProcessor();
+
+  /**
+   * A mask used when performing unsafe reads to determine if a long value contains any non-ASCII
+   * characters (i.e. any byte >= 0x80).
+   */
+  private static final long ASCII_MASK_LONG = 0x8080808080808080L;
+
   /**
    * Maximum number of bytes per Java UTF-16 char in UTF-8.
    * @see java.nio.charset.CharsetEncoder#maxBytesPerChar()
@@ -85,6 +113,18 @@ final class Utf8 {
    */
   public static final int MALFORMED = -1;
 
+  /**
+   * Used by {@code Unsafe} UTF-8 string validation logic to determine the minimum string length
+   * above which to employ an optimized algorithm for counting ASCII characters. The reason for this
+   * threshold is that for small strings, the optimization may not be beneficial or may even
+   * negatively impact performance since it requires additional logic to avoid unaligned reads
+   * (when calling {@code Unsafe.getLong}). This threshold guarantees that even if the initial
+   * offset is unaligned, we're guaranteed to make at least one call to {@code Unsafe.getLong()}
+   * which provides a performance improvement that entirely subsumes the cost of the additional
+   * logic.
+   */
+  private static final int UNSAFE_COUNT_ASCII_THRESHOLD = 16;
+
   // Other state values include the partial bytes of the incomplete
   // character to be decoded in the simplest way: we pack the bytes
   // into the state int in little-endian order.  For example:
@@ -112,7 +152,7 @@ final class Utf8 {
    * isValidUtf8(bytes, 0, bytes.length)}.
    */
   public static boolean isValidUtf8(byte[] bytes) {
-    return isValidUtf8(bytes, 0, bytes.length);
+    return processor.isValidUtf8(bytes, 0, bytes.length);
   }
 
   /**
@@ -125,7 +165,7 @@ final class Utf8 {
    * partialIsValidUtf8(bytes, index, limit) == Utf8.COMPLETE}.
    */
   public static boolean isValidUtf8(byte[] bytes, int index, int limit) {
-    return partialIsValidUtf8(bytes, index, limit) == COMPLETE;
+    return processor.isValidUtf8(bytes, index, limit);
   }
 
   /**
@@ -146,183 +186,8 @@ final class Utf8 {
    * decode the character when passed to a subsequent invocation of a
    * partial decoding method.
    */
-  public static int partialIsValidUtf8(
-      int state, byte[] bytes, int index, int limit) {
-    if (state != COMPLETE) {
-      // The previous decoding operation was incomplete (or malformed).
-      // We look for a well-formed sequence consisting of bytes from
-      // the previous decoding operation (stored in state) together
-      // with bytes from the array slice.
-      //
-      // We expect such "straddler characters" to be rare.
-
-      if (index >= limit) {  // No bytes? No progress.
-        return state;
-      }
-      int byte1 = (byte) state;
-      // byte1 is never ASCII.
-      if (byte1 < (byte) 0xE0) {
-        // two-byte form
-
-        // Simultaneously checks for illegal trailing-byte in
-        // leading position and overlong 2-byte form.
-        if (byte1 < (byte) 0xC2 ||
-            // byte2 trailing-byte test
-            bytes[index++] > (byte) 0xBF) {
-          return MALFORMED;
-        }
-      } else if (byte1 < (byte) 0xF0) {
-        // three-byte form
-
-        // Get byte2 from saved state or array
-        int byte2 = (byte) ~(state >> 8);
-        if (byte2 == 0) {
-          byte2 = bytes[index++];
-          if (index >= limit) {
-            return incompleteStateFor(byte1, byte2);
-          }
-        }
-        if (byte2 > (byte) 0xBF ||
-            // overlong? 5 most significant bits must not all be zero
-            (byte1 == (byte) 0xE0 && byte2 < (byte) 0xA0) ||
-            // illegal surrogate codepoint?
-            (byte1 == (byte) 0xED && byte2 >= (byte) 0xA0) ||
-            // byte3 trailing-byte test
-            bytes[index++] > (byte) 0xBF) {
-          return MALFORMED;
-        }
-      } else {
-        // four-byte form
-
-        // Get byte2 and byte3 from saved state or array
-        int byte2 = (byte) ~(state >> 8);
-        int byte3 = 0;
-        if (byte2 == 0) {
-          byte2 = bytes[index++];
-          if (index >= limit) {
-            return incompleteStateFor(byte1, byte2);
-          }
-        } else {
-          byte3 = (byte) (state >> 16);
-        }
-        if (byte3 == 0) {
-          byte3 = bytes[index++];
-          if (index >= limit) {
-            return incompleteStateFor(byte1, byte2, byte3);
-          }
-        }
-
-        // If we were called with state == MALFORMED, then byte1 is 0xFF,
-        // which never occurs in well-formed UTF-8, and so we will return
-        // MALFORMED again below.
-
-        if (byte2 > (byte) 0xBF ||
-            // Check that 1 <= plane <= 16.  Tricky optimized form of:
-            // if (byte1 > (byte) 0xF4 ||
-            //     byte1 == (byte) 0xF0 && byte2 < (byte) 0x90 ||
-            //     byte1 == (byte) 0xF4 && byte2 > (byte) 0x8F)
-            (((byte1 << 28) + (byte2 - (byte) 0x90)) >> 30) != 0 ||
-            // byte3 trailing-byte test
-            byte3 > (byte) 0xBF ||
-            // byte4 trailing-byte test
-             bytes[index++] > (byte) 0xBF) {
-          return MALFORMED;
-        }
-      }
-    }
-
-    return partialIsValidUtf8(bytes, index, limit);
-  }
-
-  /**
-   * Tells whether the given byte array slice is a well-formed,
-   * malformed, or incomplete UTF-8 byte sequence.  The range of bytes
-   * to be checked extends from index {@code index}, inclusive, to
-   * {@code limit}, exclusive.
-   *
-   * <p>This is a convenience method, equivalent to a call to {@code
-   * partialIsValidUtf8(Utf8.COMPLETE, bytes, index, limit)}.
-   *
-   * @return {@link #MALFORMED} if the partial byte sequence is
-   * definitely not well-formed, {@link #COMPLETE} if it is well-formed
-   * (no additional input needed), or if the byte sequence is
-   * "incomplete", i.e. apparently terminated in the middle of a character,
-   * an opaque integer "state" value containing enough information to
-   * decode the character when passed to a subsequent invocation of a
-   * partial decoding method.
-   */
-  public static int partialIsValidUtf8(
-      byte[] bytes, int index, int limit) {
-    // Optimize for 100% ASCII.
-    // Hotspot loves small simple top-level loops like this.
-    while (index < limit && bytes[index] >= 0) {
-      index++;
-    }
-
-    return (index >= limit) ? COMPLETE :
-        partialIsValidUtf8NonAscii(bytes, index, limit);
-  }
-
-  private static int partialIsValidUtf8NonAscii(
-      byte[] bytes, int index, int limit) {
-    for (;;) {
-      int byte1, byte2;
-
-      // Optimize for interior runs of ASCII bytes.
-      do {
-        if (index >= limit) {
-          return COMPLETE;
-        }
-      } while ((byte1 = bytes[index++]) >= 0);
-
-      if (byte1 < (byte) 0xE0) {
-        // two-byte form
-
-        if (index >= limit) {
-          return byte1;
-        }
-
-        // Simultaneously checks for illegal trailing-byte in
-        // leading position and overlong 2-byte form.
-        if (byte1 < (byte) 0xC2 ||
-            bytes[index++] > (byte) 0xBF) {
-          return MALFORMED;
-        }
-      } else if (byte1 < (byte) 0xF0) {
-        // three-byte form
-
-        if (index >= limit - 1) { // incomplete sequence
-          return incompleteStateFor(bytes, index, limit);
-        }
-        if ((byte2 = bytes[index++]) > (byte) 0xBF ||
-            // overlong? 5 most significant bits must not all be zero
-            (byte1 == (byte) 0xE0 && byte2 < (byte) 0xA0) ||
-            // check for illegal surrogate codepoints
-            (byte1 == (byte) 0xED && byte2 >= (byte) 0xA0) ||
-            // byte3 trailing-byte test
-            bytes[index++] > (byte) 0xBF) {
-          return MALFORMED;
-        }
-      } else {
-        // four-byte form
-
-        if (index >= limit - 2) {  // incomplete sequence
-          return incompleteStateFor(bytes, index, limit);
-        }
-        if ((byte2 = bytes[index++]) > (byte) 0xBF ||
-            // Check that 1 <= plane <= 16.  Tricky optimized form of:
-            // if (byte1 > (byte) 0xF4 ||
-            //     byte1 == (byte) 0xF0 && byte2 < (byte) 0x90 ||
-            //     byte1 == (byte) 0xF4 && byte2 > (byte) 0x8F)
-            (((byte1 << 28) + (byte2 - (byte) 0x90)) >> 30) != 0 ||
-            // byte3 trailing-byte test
-            bytes[index++] > (byte) 0xBF ||
-            // byte4 trailing-byte test
-            bytes[index++] > (byte) 0xBF) {
-          return MALFORMED;
-        }
-      }
-    }
+  public static int partialIsValidUtf8(int state, byte[] bytes, int index, int limit) {
+    return processor.partialIsValidUtf8(state, bytes, index, limit);
   }
 
   private static int incompleteStateFor(int byte1) {
@@ -352,19 +217,31 @@ final class Utf8 {
       default: throw new AssertionError();
     }
   }
-  
+
+  private static int incompleteStateFor(
+      final ByteBuffer buffer, final int byte1, final int index, final int remaining) {
+    switch (remaining) {
+      case 0:
+        return incompleteStateFor(byte1);
+      case 1:
+        return incompleteStateFor(byte1, buffer.get(index));
+      case 2:
+        return incompleteStateFor(byte1, buffer.get(index), buffer.get(index + 1));
+      default:
+        throw new AssertionError();
+    }
+  }
 
   // These UTF-8 handling methods are copied from Guava's Utf8 class with a modification to throw
   // a protocol buffer local exception. This exception is then caught in CodedOutputStream so it can
   // fallback to more lenient behavior.
   
   static class UnpairedSurrogateException extends IllegalArgumentException {
-    
     private UnpairedSurrogateException(int index, int length) {
       super("Unpaired surrogate at index " + index + " of " + length);
     }
   }
-  
+
   /**
    * Returns the number of bytes in the UTF-8-encoded form of {@code sequence}. For a string,
    * this method is equivalent to {@code string.getBytes(UTF_8).length}, but is more efficient in
@@ -426,56 +303,1381 @@ final class Utf8 {
     return utf8Length;
   }
 
-  static int encode(CharSequence sequence, byte[] bytes, int offset, int length) {
-    int utf16Length = sequence.length();
-    int j = offset;
-    int i = 0;
-    int limit = offset + length;
-    // Designed to take advantage of
-    // https://wikis.oracle.com/display/HotSpotInternals/RangeCheckElimination
-    for (char c; i < utf16Length && i + j < limit && (c = sequence.charAt(i)) < 0x80; i++) {
-      bytes[j + i] = (byte) c;
-    }
-    if (i == utf16Length) {
-      return j + utf16Length;
-    }
-    j += i;
-    for (char c; i < utf16Length; i++) {
-      c = sequence.charAt(i);
-      if (c < 0x80 && j < limit) {
-        bytes[j++] = (byte) c;
-      } else if (c < 0x800 && j <= limit - 2) { // 11 bits, two UTF-8 bytes
-        bytes[j++] = (byte) ((0xF << 6) | (c >>> 6));
-        bytes[j++] = (byte) (0x80 | (0x3F & c));
-      } else if ((c < Character.MIN_SURROGATE || Character.MAX_SURROGATE < c) && j <= limit - 3) {
-        // Maximum single-char code point is 0xFFFF, 16 bits, three UTF-8 bytes
-        bytes[j++] = (byte) ((0xF << 5) | (c >>> 12));
-        bytes[j++] = (byte) (0x80 | (0x3F & (c >>> 6)));
-        bytes[j++] = (byte) (0x80 | (0x3F & c));
-      } else if (j <= limit - 4) {
-        // Minimum code point represented by a surrogate pair is 0x10000, 17 bits, four UTF-8 bytes
-        final char low;
-        if (i + 1 == sequence.length()
-                || !Character.isSurrogatePair(c, (low = sequence.charAt(++i)))) {
-          throw new UnpairedSurrogateException((i - 1), utf16Length);
-        }
-        int codePoint = Character.toCodePoint(c, low);
-        bytes[j++] = (byte) ((0xF << 4) | (codePoint >>> 18));
-        bytes[j++] = (byte) (0x80 | (0x3F & (codePoint >>> 12)));
-        bytes[j++] = (byte) (0x80 | (0x3F & (codePoint >>> 6)));
-        bytes[j++] = (byte) (0x80 | (0x3F & codePoint));
+  static int encode(CharSequence in, byte[] out, int offset, int length) {
+    return processor.encodeUtf8(in, out, offset, length);
+  }
+  // End Guava UTF-8 methods.
+
+  /**
+   * Determines if the given {@link ByteBuffer} is a valid UTF-8 string.
+   *
+   * <p>Selects an optimal algorithm based on the type of {@link ByteBuffer} (i.e. heap or direct)
+   * and the capabilities of the platform.
+   *
+   * @param buffer the buffer to check.
+   * @see Utf8#isValidUtf8(byte[], int, int)
+   */
+  static boolean isValidUtf8(ByteBuffer buffer) {
+    return processor.isValidUtf8(buffer, buffer.position(), buffer.remaining());
+  }
+
+  /**
+   * Determines if the given {@link ByteBuffer} is a partially valid UTF-8 string.
+   *
+   * <p>Selects an optimal algorithm based on the type of {@link ByteBuffer} (i.e. heap or direct)
+   * and the capabilities of the platform.
+   *
+   * @param buffer the buffer to check.
+   * @see Utf8#partialIsValidUtf8(int, byte[], int, int)
+   */
+  static int partialIsValidUtf8(int state, ByteBuffer buffer, int index, int limit) {
+    return processor.partialIsValidUtf8(state, buffer, index, limit);
+  }
+
+  /**
+   * Encodes the given characters to the target {@link ByteBuffer} using UTF-8 encoding.
+   *
+   * <p>Selects an optimal algorithm based on the type of {@link ByteBuffer} (i.e. heap or direct)
+   * and the capabilities of the platform.
+   *
+   * @param in the source string to be encoded
+   * @param out the target buffer to receive the encoded string.
+   * @see Utf8#encode(CharSequence, byte[], int, int)
+   */
+  static void encodeUtf8(CharSequence in, ByteBuffer out) {
+    processor.encodeUtf8(in, out);
+  }
+
+  /**
+   * Counts (approximately) the number of consecutive ASCII characters in the given buffer.
+   * The byte order of the {@link ByteBuffer} does not matter, so performance can be improved if
+   * native byte order is used (i.e. no byte-swapping in {@link ByteBuffer#getLong(int)}).
+   *
+   * @param buffer the buffer to be scanned for ASCII chars
+   * @param index the starting index of the scan
+   * @param limit the limit within buffer for the scan
+   * @return the number of ASCII characters found. The stopping position will be at or
+   * before the first non-ASCII byte.
+   */
+  private static int estimateConsecutiveAscii(ByteBuffer buffer, int index, int limit) {
+    int i = index;
+    final int lim = limit - 7;
+    // This simple loop stops when we encounter a byte >= 0x80 (i.e. non-ASCII).
+    // To speed things up further, we're reading longs instead of bytes so we use a mask to
+    // determine if any byte in the current long is non-ASCII.
+    for (; i < lim && (buffer.getLong(i) & ASCII_MASK_LONG) == 0; i += 8) {}
+    return i - index;
+  }
+
+  /**
+   * A processor of UTF-8 strings, providing methods for checking validity and encoding.
+   */
+  // TODO(nathanmittler): Add support for Memory/MemoryBlock on Android.
+  abstract static class Processor {
+    /**
+     * Returns {@code true} if the given byte array slice is a
+     * well-formed UTF-8 byte sequence.  The range of bytes to be
+     * checked extends from index {@code index}, inclusive, to {@code
+     * limit}, exclusive.
+     *
+     * <p>This is a convenience method, equivalent to {@code
+     * partialIsValidUtf8(bytes, index, limit) == Utf8.COMPLETE}.
+     */
+    final boolean isValidUtf8(byte[] bytes, int index, int limit) {
+      return partialIsValidUtf8(COMPLETE, bytes, index, limit) == COMPLETE;
+    }
+
+    /**
+     * Tells whether the given byte array slice is a well-formed,
+     * malformed, or incomplete UTF-8 byte sequence.  The range of bytes
+     * to be checked extends from index {@code index}, inclusive, to
+     * {@code limit}, exclusive.
+     *
+     * @param state either {@link Utf8#COMPLETE} (if this is the initial decoding
+     * operation) or the value returned from a call to a partial decoding method
+     * for the previous bytes
+     *
+     * @return {@link #MALFORMED} if the partial byte sequence is
+     * definitely not well-formed, {@link #COMPLETE} if it is well-formed
+     * (no additional input needed), or if the byte sequence is
+     * "incomplete", i.e. apparently terminated in the middle of a character,
+     * an opaque integer "state" value containing enough information to
+     * decode the character when passed to a subsequent invocation of a
+     * partial decoding method.
+     */
+    abstract int partialIsValidUtf8(int state, byte[] bytes, int index, int limit);
+
+    /**
+     * Returns {@code true} if the given portion of the {@link ByteBuffer} is a
+     * well-formed UTF-8 byte sequence.  The range of bytes to be
+     * checked extends from index {@code index}, inclusive, to {@code
+     * limit}, exclusive.
+     *
+     * <p>This is a convenience method, equivalent to {@code
+     * partialIsValidUtf8(bytes, index, limit) == Utf8.COMPLETE}.
+     */
+    final boolean isValidUtf8(ByteBuffer buffer, int index, int limit) {
+      return partialIsValidUtf8(COMPLETE, buffer, index, limit) == COMPLETE;
+    }
+
+    /**
+     * Indicates whether or not the given buffer contains a valid UTF-8 string.
+     *
+     * @param buffer the buffer to check.
+     * @return {@code true} if the given buffer contains a valid UTF-8 string.
+     */
+    final int partialIsValidUtf8(
+        final int state, final ByteBuffer buffer, int index, final int limit) {
+      if (buffer.hasArray()) {
+        final int offset = buffer.arrayOffset();
+        return partialIsValidUtf8(state, buffer.array(), offset + index, offset + limit);
+      } else if (buffer.isDirect()){
+        return partialIsValidUtf8Direct(state, buffer, index, limit);
+      }
+      return partialIsValidUtf8Default(state, buffer, index, limit);
+    }
+
+    /**
+     * Performs validation for direct {@link ByteBuffer} instances.
+     */
+    abstract int partialIsValidUtf8Direct(
+        final int state, final ByteBuffer buffer, int index, final int limit);
+
+    /**
+     * Performs validation for {@link ByteBuffer} instances using the {@link ByteBuffer} API rather
+     * than potentially faster approaches. This first completes validation for the current
+     * character (provided by {@code state}) and then finishes validation for the sequence.
+     */
+    final int partialIsValidUtf8Default(
+        final int state, final ByteBuffer buffer, int index, final int limit) {
+      if (state != COMPLETE) {
+        // The previous decoding operation was incomplete (or malformed).
+        // We look for a well-formed sequence consisting of bytes from
+        // the previous decoding operation (stored in state) together
+        // with bytes from the array slice.
+        //
+        // We expect such "straddler characters" to be rare.
+
+        if (index >= limit) { // No bytes? No progress.
+          return state;
+        }
+
+        byte byte1 = (byte) state;
+        // byte1 is never ASCII.
+        if (byte1 < (byte) 0xE0) {
+          // two-byte form
+
+          // Simultaneously checks for illegal trailing-byte in
+          // leading position and overlong 2-byte form.
+          if (byte1 < (byte) 0xC2
+              // byte2 trailing-byte test
+              || buffer.get(index++) > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        } else if (byte1 < (byte) 0xF0) {
+          // three-byte form
+
+          // Get byte2 from saved state or array
+          byte byte2 = (byte) ~(state >> 8);
+          if (byte2 == 0) {
+            byte2 = buffer.get(index++);
+            if (index >= limit) {
+              return incompleteStateFor(byte1, byte2);
+            }
+          }
+          if (byte2 > (byte) 0xBF
+              // overlong? 5 most significant bits must not all be zero
+              || (byte1 == (byte) 0xE0 && byte2 < (byte) 0xA0)
+              // illegal surrogate codepoint?
+              || (byte1 == (byte) 0xED && byte2 >= (byte) 0xA0)
+              // byte3 trailing-byte test
+              || buffer.get(index++) > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        } else {
+          // four-byte form
+
+          // Get byte2 and byte3 from saved state or array
+          byte byte2 = (byte) ~(state >> 8);
+          byte byte3 = 0;
+          if (byte2 == 0) {
+            byte2 = buffer.get(index++);
+            if (index >= limit) {
+              return incompleteStateFor(byte1, byte2);
+            }
+          } else {
+            byte3 = (byte) (state >> 16);
+          }
+          if (byte3 == 0) {
+            byte3 = buffer.get(index++);
+            if (index >= limit) {
+              return incompleteStateFor(byte1, byte2, byte3);
+            }
+          }
+
+          // If we were called with state == MALFORMED, then byte1 is 0xFF,
+          // which never occurs in well-formed UTF-8, and so we will return
+          // MALFORMED again below.
+
+          if (byte2 > (byte) 0xBF
+              // Check that 1 <= plane <= 16.  Tricky optimized form of:
+              // if (byte1 > (byte) 0xF4 ||
+              //     byte1 == (byte) 0xF0 && byte2 < (byte) 0x90 ||
+              //     byte1 == (byte) 0xF4 && byte2 > (byte) 0x8F)
+              || (((byte1 << 28) + (byte2 - (byte) 0x90)) >> 30) != 0
+              // byte3 trailing-byte test
+              || byte3 > (byte) 0xBF
+              // byte4 trailing-byte test
+              || buffer.get(index++) > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        }
+      }
+
+      // Finish validation for the sequence.
+      return partialIsValidUtf8(buffer, index, limit);
+    }
+
+    /**
+     * Performs validation for {@link ByteBuffer} instances using the {@link ByteBuffer} API rather
+     * than potentially faster approaches.
+     */
+    private static int partialIsValidUtf8(final ByteBuffer buffer, int index, final int limit) {
+      index += estimateConsecutiveAscii(buffer, index, limit);
+
+      for (;;) {
+        // Optimize for interior runs of ASCII bytes.
+        // TODO(nathanmittler): Consider checking 8 bytes at a time after some threshold?
+        // Maybe after seeing a few in a row that are ASCII, go back to fast mode?
+        int byte1;
+        do {
+          if (index >= limit) {
+            return COMPLETE;
+          }
+        } while ((byte1 = buffer.get(index++)) >= 0);
+
+        // If we're here byte1 is not ASCII. Only need to handle 2-4 byte forms.
+        if (byte1 < (byte) 0xE0) {
+          // Two-byte form (110xxxxx 10xxxxxx)
+          if (index >= limit) {
+            // Incomplete sequence
+            return byte1;
+          }
+
+          // Simultaneously checks for illegal trailing-byte in
+          // leading position and overlong 2-byte form.
+          if (byte1 < (byte) 0xC2 || buffer.get(index) > (byte) 0xBF) {
+            return MALFORMED;
+          }
+          index++;
+        } else if (byte1 < (byte) 0xF0) {
+          // Three-byte form (1110xxxx 10xxxxxx 10xxxxxx)
+          if (index >= limit - 1) {
+            // Incomplete sequence
+            return incompleteStateFor(buffer, byte1, index, limit - index);
+          }
+
+          final byte byte2 = buffer.get(index++);
+          if (byte2 > (byte) 0xBF
+              // overlong? 5 most significant bits must not all be zero
+              || (byte1 == (byte) 0xE0 && byte2 < (byte) 0xA0)
+              // check for illegal surrogate codepoints
+              || (byte1 == (byte) 0xED && byte2 >= (byte) 0xA0)
+              // byte3 trailing-byte test
+              || buffer.get(index) > (byte) 0xBF) {
+            return MALFORMED;
+          }
+          index++;
+        } else {
+          // Four-byte form (1110xxxx 10xxxxxx 10xxxxxx 10xxxxxx)
+          if (index >= limit - 2) {
+            // Incomplete sequence
+            return incompleteStateFor(buffer, byte1, index, limit - index);
+          }
+
+          // TODO(nathanmittler): Consider using getInt() to improve performance.
+          final int byte2 = buffer.get(index++);
+          if (byte2 > (byte) 0xBF
+              // Check that 1 <= plane <= 16.  Tricky optimized form of:
+              // if (byte1 > (byte) 0xF4 ||
+              //     byte1 == (byte) 0xF0 && byte2 < (byte) 0x90 ||
+              //     byte1 == (byte) 0xF4 && byte2 > (byte) 0x8F)
+              || (((byte1 << 28) + (byte2 - (byte) 0x90)) >> 30) != 0
+              // byte3 trailing-byte test
+              || buffer.get(index++) > (byte) 0xBF
+              // byte4 trailing-byte test
+              || buffer.get(index++) > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        }
+      }
+    }
+
+    /**
+     * Encodes an input character sequence ({@code in}) to UTF-8 in the target array ({@code out}).
+     * For a string, this method is similar to
+     * <pre>{@code
+     * byte[] a = string.getBytes(UTF_8);
+     * System.arraycopy(a, 0, bytes, offset, a.length);
+     * return offset + a.length;
+     * }</pre>
+     *
+     * but is more efficient in both time and space. One key difference is that this method
+     * requires paired surrogates, and therefore does not support chunking.
+     * While {@code String.getBytes(UTF_8)} replaces unpaired surrogates with the default
+     * replacement character, this method throws {@link UnpairedSurrogateException}.
+     *
+     * <p>To ensure sufficient space in the output buffer, either call {@link #encodedLength} to
+     * compute the exact amount needed, or leave room for 
+     * {@code Utf8.MAX_BYTES_PER_CHAR * sequence.length()}, which is the largest possible number
+     * of bytes that any input can be encoded to.
+     *
+     * @param in the input character sequence to be encoded
+     * @param out the target array
+     * @param offset the starting offset in {@code bytes} to start writing at
+     * @param length the length of the {@code bytes}, starting from {@code offset}
+     * @throws UnpairedSurrogateException if {@code sequence} contains ill-formed UTF-16 (unpaired
+     *     surrogates)
+     * @throws ArrayIndexOutOfBoundsException if {@code sequence} encoded in UTF-8 is longer than
+     *     {@code bytes.length - offset}
+     * @return the new offset, equivalent to {@code offset + Utf8.encodedLength(sequence)}
+     */
+    abstract int encodeUtf8(CharSequence in, byte[] out, int offset, int length);
+
+    /**
+     * Encodes an input character sequence ({@code in}) to UTF-8 in the target buffer ({@code out}).
+     * Upon returning from this method, the {@code out} position will point to the position after
+     * the last encoded byte. This method requires paired surrogates, and therefore does not
+     * support chunking.
+     *
+     * <p>To ensure sufficient space in the output buffer, either call {@link #encodedLength} to
+     * compute the exact amount needed, or leave room for
+     * {@code Utf8.MAX_BYTES_PER_CHAR * in.length()}, which is the largest possible number
+     * of bytes that any input can be encoded to.
+     *
+     * @param in the source character sequence to be encoded
+     * @param out the target buffer
+     * @throws UnpairedSurrogateException if {@code in} contains ill-formed UTF-16 (unpaired
+     *     surrogates)
+     * @throws ArrayIndexOutOfBoundsException if {@code in} encoded in UTF-8 is longer than
+     *     {@code out.remaining()}
+     */
+    final void encodeUtf8(CharSequence in, ByteBuffer out) {
+      if (out.hasArray()) {
+        final int offset = out.arrayOffset();
+        int endIndex =
+            Utf8.encode(in, out.array(), offset + out.position(), out.remaining());
+        out.position(endIndex - offset);
+      } else if (out.isDirect()) {
+        encodeUtf8Direct(in, out);
       } else {
-        // If we are surrogates and we're not a surrogate pair, always throw an
-        // IllegalArgumentException instead of an ArrayOutOfBoundsException.
-        if ((Character.MIN_SURROGATE <= c && c <= Character.MAX_SURROGATE)
-            && (i + 1 == sequence.length()
-                || !Character.isSurrogatePair(c, sequence.charAt(i + 1)))) {
-          throw new UnpairedSurrogateException(i, utf16Length);
+        encodeUtf8Default(in, out);
+      }
+    }
+
+    /**
+     * Encodes the input character sequence to a direct {@link ByteBuffer} instance.
+     */
+    abstract void encodeUtf8Direct(CharSequence in, ByteBuffer out);
+
+    /**
+     * Encodes the input character sequence to a {@link ByteBuffer} instance using the {@link
+     * ByteBuffer} API, rather than potentially faster approaches.
+     */
+    final void encodeUtf8Default(CharSequence in, ByteBuffer out) {
+      final int inLength = in.length();
+      int outIx = out.position();
+      int inIx = 0;
+
+      // Since ByteBuffer.putXXX() already checks boundaries for us, no need to explicitly check
+      // access. Assume the buffer is big enough and let it handle the out of bounds exception
+      // if it occurs.
+      try {
+        // Designed to take advantage of
+        // https://wikis.oracle.com/display/HotSpotInternals/RangeCheckElimination
+        for (char c; inIx < inLength && (c = in.charAt(inIx)) < 0x80; ++inIx) {
+          out.put(outIx + inIx, (byte) c);
         }
-        throw new ArrayIndexOutOfBoundsException("Failed writing " + c + " at index " + j);
+        if (inIx == inLength) {
+          // Successfully encoded the entire string.
+          out.position(outIx + inIx);
+          return;
+        }
+
+        outIx += inIx;
+        for (char c; inIx < inLength; ++inIx, ++outIx) {
+          c = in.charAt(inIx);
+          if (c < 0x80) {
+            // One byte (0xxx xxxx)
+            out.put(outIx, (byte) c);
+          } else if (c < 0x800) {
+            // Two bytes (110x xxxx 10xx xxxx)
+
+            // Benchmarks show put performs better than putShort here (for HotSpot).
+            out.put(outIx++, (byte) (0xC0 | (c >>> 6)));
+            out.put(outIx, (byte) (0x80 | (0x3F & c)));
+          } else if (c < MIN_SURROGATE || MAX_SURROGATE < c) {
+            // Three bytes (1110 xxxx 10xx xxxx 10xx xxxx)
+            // Maximum single-char code point is 0xFFFF, 16 bits.
+
+            // Benchmarks show put performs better than putShort here (for HotSpot).
+            out.put(outIx++, (byte) (0xE0 | (c >>> 12)));
+            out.put(outIx++, (byte) (0x80 | (0x3F & (c >>> 6))));
+            out.put(outIx, (byte) (0x80 | (0x3F & c)));
+          } else {
+            // Four bytes (1111 xxxx 10xx xxxx 10xx xxxx 10xx xxxx)
+
+            // Minimum code point represented by a surrogate pair is 0x10000, 17 bits, four UTF-8
+            // bytes
+            final char low;
+            if (inIx + 1 == inLength || !isSurrogatePair(c, (low = in.charAt(++inIx)))) {
+              throw new UnpairedSurrogateException(inIx, inLength);
+            }
+            // TODO(nathanmittler): Consider using putInt() to improve performance.
+            int codePoint = toCodePoint(c, low);
+            out.put(outIx++, (byte) ((0xF << 4) | (codePoint >>> 18)));
+            out.put(outIx++, (byte) (0x80 | (0x3F & (codePoint >>> 12))));
+            out.put(outIx++, (byte) (0x80 | (0x3F & (codePoint >>> 6))));
+            out.put(outIx, (byte) (0x80 | (0x3F & codePoint)));
+          }
+        }
+
+        // Successfully encoded the entire string.
+        out.position(outIx);
+      } catch (IndexOutOfBoundsException e) {
+        // TODO(nathanmittler): Consider making the API throw IndexOutOfBoundsException instead.
+
+        // If we failed in the outer ASCII loop, outIx will not have been updated. In this case,
+        // use inIx to determine the bad write index.
+        int badWriteIndex = out.position() + Math.max(inIx, outIx - out.position() + 1);
+        throw new ArrayIndexOutOfBoundsException(
+            "Failed writing " + in.charAt(inIx) + " at index " + badWriteIndex);
       }
     }
-    return j;
   }
-  // End Guava UTF-8 methods.
+
+  /**
+   * {@link Processor} implementation that does not use any {@code sun.misc.Unsafe} methods.
+   */
+  static final class SafeProcessor extends Processor {
+    @Override
+    int partialIsValidUtf8(int state, byte[] bytes, int index, int limit) {
+      if (state != COMPLETE) {
+        // The previous decoding operation was incomplete (or malformed).
+        // We look for a well-formed sequence consisting of bytes from
+        // the previous decoding operation (stored in state) together
+        // with bytes from the array slice.
+        //
+        // We expect such "straddler characters" to be rare.
+
+        if (index >= limit) {  // No bytes? No progress.
+          return state;
+        }
+        int byte1 = (byte) state;
+        // byte1 is never ASCII.
+        if (byte1 < (byte) 0xE0) {
+          // two-byte form
+
+          // Simultaneously checks for illegal trailing-byte in
+          // leading position and overlong 2-byte form.
+          if (byte1 < (byte) 0xC2
+              // byte2 trailing-byte test
+              || bytes[index++] > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        } else if (byte1 < (byte) 0xF0) {
+          // three-byte form
+
+          // Get byte2 from saved state or array
+          int byte2 = (byte) ~(state >> 8);
+          if (byte2 == 0) {
+            byte2 = bytes[index++];
+            if (index >= limit) {
+              return incompleteStateFor(byte1, byte2);
+            }
+          }
+          if (byte2 > (byte) 0xBF
+              // overlong? 5 most significant bits must not all be zero
+              || (byte1 == (byte) 0xE0 && byte2 < (byte) 0xA0)
+              // illegal surrogate codepoint?
+              || (byte1 == (byte) 0xED && byte2 >= (byte) 0xA0)
+              // byte3 trailing-byte test
+              || bytes[index++] > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        } else {
+          // four-byte form
+
+          // Get byte2 and byte3 from saved state or array
+          int byte2 = (byte) ~(state >> 8);
+          int byte3 = 0;
+          if (byte2 == 0) {
+            byte2 = bytes[index++];
+            if (index >= limit) {
+              return incompleteStateFor(byte1, byte2);
+            }
+          } else {
+            byte3 = (byte) (state >> 16);
+          }
+          if (byte3 == 0) {
+            byte3 = bytes[index++];
+            if (index >= limit) {
+              return incompleteStateFor(byte1, byte2, byte3);
+            }
+          }
+
+          // If we were called with state == MALFORMED, then byte1 is 0xFF,
+          // which never occurs in well-formed UTF-8, and so we will return
+          // MALFORMED again below.
+
+          if (byte2 > (byte) 0xBF
+              // Check that 1 <= plane <= 16.  Tricky optimized form of:
+              // if (byte1 > (byte) 0xF4 ||
+              //     byte1 == (byte) 0xF0 && byte2 < (byte) 0x90 ||
+              //     byte1 == (byte) 0xF4 && byte2 > (byte) 0x8F)
+              || (((byte1 << 28) + (byte2 - (byte) 0x90)) >> 30) != 0
+              // byte3 trailing-byte test
+              || byte3 > (byte) 0xBF
+              // byte4 trailing-byte test
+              || bytes[index++] > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        }
+      }
+
+      return partialIsValidUtf8(bytes, index, limit);
+    }
+
+    @Override
+    int partialIsValidUtf8Direct(int state, ByteBuffer buffer, int index, int limit) {
+      // For safe processing, we have to use the ByteBuffer API.
+      return partialIsValidUtf8Default(state, buffer, index, limit);
+    }
+
+    @Override
+    int encodeUtf8(CharSequence in, byte[] out, int offset, int length) {
+      int utf16Length = in.length();
+      int j = offset;
+      int i = 0;
+      int limit = offset + length;
+      // Designed to take advantage of
+      // https://wikis.oracle.com/display/HotSpotInternals/RangeCheckElimination
+      for (char c; i < utf16Length && i + j < limit && (c = in.charAt(i)) < 0x80; i++) {
+        out[j + i] = (byte) c;
+      }
+      if (i == utf16Length) {
+        return j + utf16Length;
+      }
+      j += i;
+      for (char c; i < utf16Length; i++) {
+        c = in.charAt(i);
+        if (c < 0x80 && j < limit) {
+          out[j++] = (byte) c;
+        } else if (c < 0x800 && j <= limit - 2) { // 11 bits, two UTF-8 bytes
+          out[j++] = (byte) ((0xF << 6) | (c >>> 6));
+          out[j++] = (byte) (0x80 | (0x3F & c));
+        } else if ((c < Character.MIN_SURROGATE || Character.MAX_SURROGATE < c) && j <= limit - 3) {
+          // Maximum single-char code point is 0xFFFF, 16 bits, three UTF-8 bytes
+          out[j++] = (byte) ((0xF << 5) | (c >>> 12));
+          out[j++] = (byte) (0x80 | (0x3F & (c >>> 6)));
+          out[j++] = (byte) (0x80 | (0x3F & c));
+        } else if (j <= limit - 4) {
+          // Minimum code point represented by a surrogate pair is 0x10000, 17 bits,
+          // four UTF-8 bytes
+          final char low;
+          if (i + 1 == in.length()
+                  || !Character.isSurrogatePair(c, (low = in.charAt(++i)))) {
+            throw new UnpairedSurrogateException((i - 1), utf16Length);
+          }
+          int codePoint = Character.toCodePoint(c, low);
+          out[j++] = (byte) ((0xF << 4) | (codePoint >>> 18));
+          out[j++] = (byte) (0x80 | (0x3F & (codePoint >>> 12)));
+          out[j++] = (byte) (0x80 | (0x3F & (codePoint >>> 6)));
+          out[j++] = (byte) (0x80 | (0x3F & codePoint));
+        } else {
+          // If we are surrogates and we're not a surrogate pair, always throw an
+          // UnpairedSurrogateException instead of an ArrayOutOfBoundsException.
+          if ((Character.MIN_SURROGATE <= c && c <= Character.MAX_SURROGATE)
+              && (i + 1 == in.length()
+                  || !Character.isSurrogatePair(c, in.charAt(i + 1)))) {
+            throw new UnpairedSurrogateException(i, utf16Length);
+          }
+          throw new ArrayIndexOutOfBoundsException("Failed writing " + c + " at index " + j);
+        }
+      }
+      return j;
+    }
+
+    @Override
+    void encodeUtf8Direct(CharSequence in, ByteBuffer out) {
+      // For safe processing, we have to use the ByteBuffer API.
+      encodeUtf8Default(in, out);
+    }
+
+    private static int partialIsValidUtf8(byte[] bytes, int index, int limit) {
+      // Optimize for 100% ASCII (Hotspot loves small simple top-level loops like this).
+      // This simple loop stops when we encounter a byte >= 0x80 (i.e. non-ASCII).
+      while (index < limit && bytes[index] >= 0) {
+        index++;
+      }
+
+      return (index >= limit) ? COMPLETE : partialIsValidUtf8NonAscii(bytes, index, limit);
+    }
+
+    private static int partialIsValidUtf8NonAscii(byte[] bytes, int index, int limit) {
+      for (;;) {
+        int byte1, byte2;
+
+        // Optimize for interior runs of ASCII bytes.
+        do {
+          if (index >= limit) {
+            return COMPLETE;
+          }
+        } while ((byte1 = bytes[index++]) >= 0);
+
+        if (byte1 < (byte) 0xE0) {
+          // two-byte form
+
+          if (index >= limit) {
+            // Incomplete sequence
+            return byte1;
+          }
+
+          // Simultaneously checks for illegal trailing-byte in
+          // leading position and overlong 2-byte form.
+          if (byte1 < (byte) 0xC2
+              || bytes[index++] > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        } else if (byte1 < (byte) 0xF0) {
+          // three-byte form
+
+          if (index >= limit - 1) { // incomplete sequence
+            return incompleteStateFor(bytes, index, limit);
+          }
+          if ((byte2 = bytes[index++]) > (byte) 0xBF
+              // overlong? 5 most significant bits must not all be zero
+              || (byte1 == (byte) 0xE0 && byte2 < (byte) 0xA0)
+              // check for illegal surrogate codepoints
+              || (byte1 == (byte) 0xED && byte2 >= (byte) 0xA0)
+              // byte3 trailing-byte test
+              || bytes[index++] > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        } else {
+          // four-byte form
+
+          if (index >= limit - 2) {  // incomplete sequence
+            return incompleteStateFor(bytes, index, limit);
+          }
+          if ((byte2 = bytes[index++]) > (byte) 0xBF
+              // Check that 1 <= plane <= 16.  Tricky optimized form of:
+              // if (byte1 > (byte) 0xF4 ||
+              //     byte1 == (byte) 0xF0 && byte2 < (byte) 0x90 ||
+              //     byte1 == (byte) 0xF4 && byte2 > (byte) 0x8F)
+              || (((byte1 << 28) + (byte2 - (byte) 0x90)) >> 30) != 0
+              // byte3 trailing-byte test
+              || bytes[index++] > (byte) 0xBF
+              // byte4 trailing-byte test
+              || bytes[index++] > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        }
+      }
+    }
+  }
+
+  /**
+   * {@link Processor} that uses {@code sun.misc.Unsafe} where possible to improve performance.
+   */
+  static final class UnsafeProcessor extends Processor {
+    private static final sun.misc.Unsafe UNSAFE = getUnsafe();
+    private static final long BUFFER_ADDRESS_OFFSET =
+        fieldOffset(field(Buffer.class, "address"));
+    private static final int ARRAY_BASE_OFFSET = byteArrayBaseOffset();
+
+    /**
+     * We only use Unsafe operations if we have access to direct {@link ByteBuffer}'s address
+     * and the array base offset is a multiple of 8 (needed by Unsafe.getLong()).
+     */
+    private static final boolean AVAILABLE =
+        BUFFER_ADDRESS_OFFSET != -1 && ARRAY_BASE_OFFSET % 8 == 0;
+
+    /**
+     * Indicates whether or not all required unsafe operations are supported on this platform.
+     */
+    static boolean isAvailable() {
+      return AVAILABLE;
+    }
+
+    @Override
+    int partialIsValidUtf8(int state, byte[] bytes, final int index, final int limit) {
+      if ((index | limit | bytes.length - limit) < 0) {
+        throw new ArrayIndexOutOfBoundsException(
+            String.format("Array length=%d, index=%d, limit=%d", bytes.length, index, limit));
+      }
+      long offset = ARRAY_BASE_OFFSET + index;
+      final long offsetLimit = ARRAY_BASE_OFFSET + limit;
+      if (state != COMPLETE) {
+        // The previous decoding operation was incomplete (or malformed).
+        // We look for a well-formed sequence consisting of bytes from
+        // the previous decoding operation (stored in state) together
+        // with bytes from the array slice.
+        //
+        // We expect such "straddler characters" to be rare.
+
+        if (offset >= offsetLimit) {  // No bytes? No progress.
+          return state;
+        }
+        int byte1 = (byte) state;
+        // byte1 is never ASCII.
+        if (byte1 < (byte) 0xE0) {
+          // two-byte form
+
+          // Simultaneously checks for illegal trailing-byte in
+          // leading position and overlong 2-byte form.
+          if (byte1 < (byte) 0xC2
+              // byte2 trailing-byte test
+              || UNSAFE.getByte(bytes, offset++) > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        } else if (byte1 < (byte) 0xF0) {
+          // three-byte form
+
+          // Get byte2 from saved state or array
+          int byte2 = (byte) ~(state >> 8);
+          if (byte2 == 0) {
+            byte2 = UNSAFE.getByte(bytes, offset++);
+            if (offset >= offsetLimit) {
+              return incompleteStateFor(byte1, byte2);
+            }
+          }
+          if (byte2 > (byte) 0xBF
+              // overlong? 5 most significant bits must not all be zero
+              || (byte1 == (byte) 0xE0 && byte2 < (byte) 0xA0)
+              // illegal surrogate codepoint?
+              || (byte1 == (byte) 0xED && byte2 >= (byte) 0xA0)
+              // byte3 trailing-byte test
+              || UNSAFE.getByte(bytes, offset++) > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        } else {
+          // four-byte form
+
+          // Get byte2 and byte3 from saved state or array
+          int byte2 = (byte) ~(state >> 8);
+          int byte3 = 0;
+          if (byte2 == 0) {
+            byte2 = UNSAFE.getByte(bytes, offset++);
+            if (offset >= offsetLimit) {
+              return incompleteStateFor(byte1, byte2);
+            }
+          } else {
+            byte3 = (byte) (state >> 16);
+          }
+          if (byte3 == 0) {
+            byte3 = UNSAFE.getByte(bytes, offset++);
+            if (offset >= offsetLimit) {
+              return incompleteStateFor(byte1, byte2, byte3);
+            }
+          }
+
+          // If we were called with state == MALFORMED, then byte1 is 0xFF,
+          // which never occurs in well-formed UTF-8, and so we will return
+          // MALFORMED again below.
+
+          if (byte2 > (byte) 0xBF
+              // Check that 1 <= plane <= 16.  Tricky optimized form of:
+              // if (byte1 > (byte) 0xF4 ||
+              //     byte1 == (byte) 0xF0 && byte2 < (byte) 0x90 ||
+              //     byte1 == (byte) 0xF4 && byte2 > (byte) 0x8F)
+              || (((byte1 << 28) + (byte2 - (byte) 0x90)) >> 30) != 0
+              // byte3 trailing-byte test
+              || byte3 > (byte) 0xBF
+              // byte4 trailing-byte test
+              || UNSAFE.getByte(bytes, offset++) > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        }
+      }
+
+      return partialIsValidUtf8(bytes, offset, (int) (offsetLimit - offset));
+    }
+
+    @Override
+    int partialIsValidUtf8Direct(
+        final int state, ByteBuffer buffer, final int index, final int limit) {
+      if ((index | limit | buffer.limit() - limit) < 0) {
+        throw new ArrayIndexOutOfBoundsException(
+            String.format("buffer limit=%d, index=%d, limit=%d", buffer.limit(), index, limit));
+      }
+      long address = addressOffset(buffer) + index;
+      final long addressLimit = address + (limit - index);
+      if (state != COMPLETE) {
+        // The previous decoding operation was incomplete (or malformed).
+        // We look for a well-formed sequence consisting of bytes from
+        // the previous decoding operation (stored in state) together
+        // with bytes from the array slice.
+        //
+        // We expect such "straddler characters" to be rare.
+
+        if (address >= addressLimit) { // No bytes? No progress.
+          return state;
+        }
+
+        final int byte1 = (byte) state;
+        // byte1 is never ASCII.
+        if (byte1 < (byte) 0xE0) {
+          // two-byte form
+
+          // Simultaneously checks for illegal trailing-byte in
+          // leading position and overlong 2-byte form.
+          if (byte1 < (byte) 0xC2
+              // byte2 trailing-byte test
+              || UNSAFE.getByte(address++) > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        } else if (byte1 < (byte) 0xF0) {
+          // three-byte form
+
+          // Get byte2 from saved state or array
+          int byte2 = (byte) ~(state >> 8);
+          if (byte2 == 0) {
+            byte2 = UNSAFE.getByte(address++);
+            if (address >= addressLimit) {
+              return incompleteStateFor(byte1, byte2);
+            }
+          }
+          if (byte2 > (byte) 0xBF
+              // overlong? 5 most significant bits must not all be zero
+              || (byte1 == (byte) 0xE0 && byte2 < (byte) 0xA0)
+              // illegal surrogate codepoint?
+              || (byte1 == (byte) 0xED && byte2 >= (byte) 0xA0)
+              // byte3 trailing-byte test
+              || UNSAFE.getByte(address++) > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        } else {
+          // four-byte form
+
+          // Get byte2 and byte3 from saved state or array
+          int byte2 = (byte) ~(state >> 8);
+          int byte3 = 0;
+          if (byte2 == 0) {
+            byte2 = UNSAFE.getByte(address++);
+            if (address >= addressLimit) {
+              return incompleteStateFor(byte1, byte2);
+            }
+          } else {
+            byte3 = (byte) (state >> 16);
+          }
+          if (byte3 == 0) {
+            byte3 = UNSAFE.getByte(address++);
+            if (address >= addressLimit) {
+              return incompleteStateFor(byte1, byte2, byte3);
+            }
+          }
+
+          // If we were called with state == MALFORMED, then byte1 is 0xFF,
+          // which never occurs in well-formed UTF-8, and so we will return
+          // MALFORMED again below.
+
+          if (byte2 > (byte) 0xBF
+              // Check that 1 <= plane <= 16.  Tricky optimized form of:
+              // if (byte1 > (byte) 0xF4 ||
+              //     byte1 == (byte) 0xF0 && byte2 < (byte) 0x90 ||
+              //     byte1 == (byte) 0xF4 && byte2 > (byte) 0x8F)
+              || (((byte1 << 28) + (byte2 - (byte) 0x90)) >> 30) != 0
+              // byte3 trailing-byte test
+              || byte3 > (byte) 0xBF
+              // byte4 trailing-byte test
+              || UNSAFE.getByte(address++) > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        }
+      }
+
+      return partialIsValidUtf8(address, (int) (addressLimit - address));
+    }
+
+    @Override
+    int encodeUtf8(final CharSequence in, final byte[] out, final int offset, final int length) {
+      long outIx = ARRAY_BASE_OFFSET + offset;
+      final long outLimit = outIx + length;
+      final int inLimit = in.length();
+      if (inLimit > length || out.length - length < offset) {
+        // Not even enough room for an ASCII-encoded string.
+        throw new ArrayIndexOutOfBoundsException(
+            "Failed writing " + in.charAt(inLimit - 1) + " at index " + (offset + length));
+      }
+
+      // Designed to take advantage of
+      // https://wikis.oracle.com/display/HotSpotInternals/RangeCheckElimination
+      int inIx = 0;
+      for (char c; inIx < inLimit && (c = in.charAt(inIx)) < 0x80; ++inIx) {
+        UNSAFE.putByte(out, outIx++, (byte) c);
+      }
+      if (inIx == inLimit) {
+        // We're done, it was ASCII encoded.
+        return (int) (outIx - ARRAY_BASE_OFFSET);
+      }
+
+      for (char c; inIx < inLimit; ++inIx) {
+        c = in.charAt(inIx);
+        if (c < 0x80 && outIx < outLimit) {
+          UNSAFE.putByte(out, outIx++, (byte) c);
+        } else if (c < 0x800 && outIx <= outLimit - 2L) { // 11 bits, two UTF-8 bytes
+          UNSAFE.putByte(out, outIx++, (byte) ((0xF << 6) | (c >>> 6)));
+          UNSAFE.putByte(out, outIx++, (byte) (0x80 | (0x3F & c)));
+        } else if ((c < MIN_SURROGATE || MAX_SURROGATE < c) && outIx <= outLimit - 3L) {
+          // Maximum single-char code point is 0xFFFF, 16 bits, three UTF-8 bytes
+          UNSAFE.putByte(out, outIx++, (byte) ((0xF << 5) | (c >>> 12)));
+          UNSAFE.putByte(out, outIx++, (byte) (0x80 | (0x3F & (c >>> 6))));
+          UNSAFE.putByte(out, outIx++, (byte) (0x80 | (0x3F & c)));
+        } else if (outIx <= outLimit - 4L) {
+          // Minimum code point represented by a surrogate pair is 0x10000, 17 bits, four UTF-8
+          // bytes
+          final char low;
+          if (inIx + 1 == inLimit || !isSurrogatePair(c, (low = in.charAt(++inIx)))) {
+            throw new UnpairedSurrogateException((inIx - 1), inLimit);
+          }
+          int codePoint = toCodePoint(c, low);
+          UNSAFE.putByte(out, outIx++, (byte) ((0xF << 4) | (codePoint >>> 18)));
+          UNSAFE.putByte(out, outIx++, (byte) (0x80 | (0x3F & (codePoint >>> 12))));
+          UNSAFE.putByte(out, outIx++, (byte) (0x80 | (0x3F & (codePoint >>> 6))));
+          UNSAFE.putByte(out, outIx++, (byte) (0x80 | (0x3F & codePoint)));
+        } else {
+          if ((MIN_SURROGATE <= c && c <= MAX_SURROGATE)
+              && (inIx + 1 == inLimit || !isSurrogatePair(c, in.charAt(inIx + 1)))) {
+            // We are surrogates and we're not a surrogate pair.
+            throw new UnpairedSurrogateException(inIx, inLimit);
+          }
+          // Not enough space in the output buffer.
+          throw new ArrayIndexOutOfBoundsException("Failed writing " + c + " at index " + outIx);
+        }
+      }
+
+      // All bytes have been encoded.
+      return (int) (outIx - ARRAY_BASE_OFFSET);
+    }
+
+    @Override
+    void encodeUtf8Direct(CharSequence in, ByteBuffer out) {
+      final long address = addressOffset(out);
+      long outIx = address + out.position();
+      final long outLimit = address + out.limit();
+      final int inLimit = in.length();
+      if (inLimit > outLimit - outIx) {
+        // Not even enough room for an ASCII-encoded string.
+        throw new ArrayIndexOutOfBoundsException(
+            "Failed writing " + in.charAt(inLimit - 1) + " at index " + out.limit());
+      }
+
+      // Designed to take advantage of
+      // https://wikis.oracle.com/display/HotSpotInternals/RangeCheckElimination
+      int inIx = 0;
+      for (char c; inIx < inLimit && (c = in.charAt(inIx)) < 0x80; ++inIx) {
+        UNSAFE.putByte(outIx++, (byte) c);
+      }
+      if (inIx == inLimit) {
+        // We're done, it was ASCII encoded.
+        out.position((int) (outIx - address));
+        return;
+      }
+
+      for (char c; inIx < inLimit; ++inIx) {
+        c = in.charAt(inIx);
+        if (c < 0x80 && outIx < outLimit) {
+          UNSAFE.putByte(outIx++, (byte) c);
+        } else if (c < 0x800 && outIx <= outLimit - 2L) { // 11 bits, two UTF-8 bytes
+          UNSAFE.putByte(outIx++, (byte) ((0xF << 6) | (c >>> 6)));
+          UNSAFE.putByte(outIx++, (byte) (0x80 | (0x3F & c)));
+        } else if ((c < MIN_SURROGATE || MAX_SURROGATE < c) && outIx <= outLimit - 3L) {
+          // Maximum single-char code point is 0xFFFF, 16 bits, three UTF-8 bytes
+          UNSAFE.putByte(outIx++, (byte) ((0xF << 5) | (c >>> 12)));
+          UNSAFE.putByte(outIx++, (byte) (0x80 | (0x3F & (c >>> 6))));
+          UNSAFE.putByte(outIx++, (byte) (0x80 | (0x3F & c)));
+        } else if (outIx <= outLimit - 4L) {
+          // Minimum code point represented by a surrogate pair is 0x10000, 17 bits, four UTF-8
+          // bytes
+          final char low;
+          if (inIx + 1 == inLimit || !isSurrogatePair(c, (low = in.charAt(++inIx)))) {
+            throw new UnpairedSurrogateException((inIx - 1), inLimit);
+          }
+          int codePoint = toCodePoint(c, low);
+          UNSAFE.putByte(outIx++, (byte) ((0xF << 4) | (codePoint >>> 18)));
+          UNSAFE.putByte(outIx++, (byte) (0x80 | (0x3F & (codePoint >>> 12))));
+          UNSAFE.putByte(outIx++, (byte) (0x80 | (0x3F & (codePoint >>> 6))));
+          UNSAFE.putByte(outIx++, (byte) (0x80 | (0x3F & codePoint)));
+        } else {
+          if ((MIN_SURROGATE <= c && c <= MAX_SURROGATE)
+              && (inIx + 1 == inLimit || !isSurrogatePair(c, in.charAt(inIx + 1)))) {
+            // We are surrogates and we're not a surrogate pair.
+            throw new UnpairedSurrogateException(inIx, inLimit);
+          }
+          // Not enough space in the output buffer.
+          throw new ArrayIndexOutOfBoundsException("Failed writing " + c + " at index " + outIx);
+        }
+      }
+
+      // All bytes have been encoded.
+      out.position((int) (outIx - address));
+    }
+
+    /**
+     * Counts (approximately) the number of consecutive ASCII characters starting from the given
+     * position, using the most efficient method available to the platform.
+     *
+     * @param bytes the array containing the character sequence
+     * @param offset the offset position of the index (same as index + arrayBaseOffset)
+     * @param maxChars the maximum number of characters to count
+     * @return the number of ASCII characters found. The stopping position will be at or
+     * before the first non-ASCII byte.
+     */
+    private static int unsafeEstimateConsecutiveAscii(
+        byte[] bytes, long offset, final int maxChars) {
+      int remaining = maxChars;
+      if (remaining < UNSAFE_COUNT_ASCII_THRESHOLD) {
+        // Don't bother with small strings.
+        return 0;
+      }
+
+      // Read bytes until 8-byte aligned so that we can read longs in the loop below.
+      // Byte arrays are already either 8 or 16-byte aligned, so we just need to make sure that
+      // the index (relative to the start of the array) is also 8-byte aligned. We do this by
+      // ANDing the index with 7 to determine the number of bytes that need to be read before
+      // we're 8-byte aligned.
+      final int unaligned = (int) offset & 7;
+      for (int j = unaligned; j > 0; j--) {
+        if (UNSAFE.getByte(bytes, offset++) < 0) {
+          return unaligned - j;
+        }
+      }
+
+      // This simple loop stops when we encounter a byte >= 0x80 (i.e. non-ASCII).
+      // To speed things up further, we're reading longs instead of bytes so we use a mask to
+      // determine if any byte in the current long is non-ASCII.
+      remaining -= unaligned;
+      for (; remaining >= 8 && (UNSAFE.getLong(bytes, offset) & ASCII_MASK_LONG) == 0;
+          offset += 8, remaining -= 8) {}
+      return maxChars - remaining;
+    }
+
+    /**
+     * Same as {@link Utf8#estimateConsecutiveAscii(ByteBuffer, int, int)} except that it uses the
+     * most efficient method available to the platform.
+     */
+    private static int unsafeEstimateConsecutiveAscii(long address, final int maxChars) {
+      int remaining = maxChars;
+      if (remaining < UNSAFE_COUNT_ASCII_THRESHOLD) {
+        // Don't bother with small strings.
+        return 0;
+      }
+
+      // Read bytes until 8-byte aligned so that we can read longs in the loop below.
+      // We do this by ANDing the address with 7 to determine the number of bytes that need to
+      // be read before we're 8-byte aligned.
+      final int unaligned = (int) address & 7;
+      for (int j = unaligned; j > 0; j--) {
+        if (UNSAFE.getByte(address++) < 0) {
+          return unaligned - j;
+        }
+      }
+
+      // This simple loop stops when we encounter a byte >= 0x80 (i.e. non-ASCII).
+      // To speed things up further, we're reading longs instead of bytes so we use a mask to
+      // determine if any byte in the current long is non-ASCII.
+      remaining -= unaligned;
+      for (; remaining >= 8 && (UNSAFE.getLong(address) & ASCII_MASK_LONG) == 0;
+          address += 8, remaining -= 8) {}
+      return maxChars - remaining;
+    }
+
+    private static int partialIsValidUtf8(final byte[] bytes, long offset, int remaining) {
+      // Skip past ASCII characters as quickly as possible. 
+      final int skipped = unsafeEstimateConsecutiveAscii(bytes, offset, remaining);
+      remaining -= skipped;
+      offset += skipped;
+
+      for (;;) {
+        // Optimize for interior runs of ASCII bytes.
+        // TODO(nathanmittler): Consider checking 8 bytes at a time after some threshold?
+        // Maybe after seeing a few in a row that are ASCII, go back to fast mode?
+        int byte1 = 0;
+        for (; remaining > 0 && (byte1 = UNSAFE.getByte(bytes, offset++)) >= 0; --remaining) {
+        }
+        if (remaining == 0) {
+          return COMPLETE;
+        }
+        remaining--;
+
+        // If we're here byte1 is not ASCII. Only need to handle 2-4 byte forms.
+        if (byte1 < (byte) 0xE0) {
+          // Two-byte form (110xxxxx 10xxxxxx)
+          if (remaining == 0) {
+            // Incomplete sequence
+            return byte1;
+          }
+          remaining--;
+
+          // Simultaneously checks for illegal trailing-byte in
+          // leading position and overlong 2-byte form.
+          if (byte1 < (byte) 0xC2
+              || UNSAFE.getByte(bytes, offset++) > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        } else if (byte1 < (byte) 0xF0) {
+          // Three-byte form (1110xxxx 10xxxxxx 10xxxxxx)
+          if (remaining < 2) {
+            // Incomplete sequence
+            return unsafeIncompleteStateFor(bytes, byte1, offset, remaining);
+          }
+          remaining -= 2;
+
+          final int byte2;
+          if ((byte2 = UNSAFE.getByte(bytes, offset++)) > (byte) 0xBF
+              // overlong? 5 most significant bits must not all be zero
+              || (byte1 == (byte) 0xE0 && byte2 < (byte) 0xA0)
+              // check for illegal surrogate codepoints
+              || (byte1 == (byte) 0xED && byte2 >= (byte) 0xA0)
+              // byte3 trailing-byte test
+              || UNSAFE.getByte(bytes, offset++) > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        } else {
+          // Four-byte form (1110xxxx 10xxxxxx 10xxxxxx 10xxxxxx)
+          if (remaining < 3) {
+            // Incomplete sequence
+            return unsafeIncompleteStateFor(bytes, byte1, offset, remaining);
+          }
+          remaining -= 3;
+
+          final int byte2;
+          if ((byte2 = UNSAFE.getByte(bytes, offset++)) > (byte) 0xBF
+              // Check that 1 <= plane <= 16.  Tricky optimized form of:
+              // if (byte1 > (byte) 0xF4 ||
+              //     byte1 == (byte) 0xF0 && byte2 < (byte) 0x90 ||
+              //     byte1 == (byte) 0xF4 && byte2 > (byte) 0x8F)
+              || (((byte1 << 28) + (byte2 - (byte) 0x90)) >> 30) != 0
+              // byte3 trailing-byte test
+              || UNSAFE.getByte(bytes, offset++) > (byte) 0xBF
+              // byte4 trailing-byte test
+              || UNSAFE.getByte(bytes, offset++) > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        }
+      }
+    }
+
+    private static int partialIsValidUtf8(long address, int remaining) {
+      // Skip past ASCII characters as quickly as possible.
+      final int skipped = unsafeEstimateConsecutiveAscii(address, remaining);
+      address += skipped;
+      remaining -= skipped;
+
+      for (;;) {
+        // Optimize for interior runs of ASCII bytes.
+        // TODO(nathanmittler): Consider checking 8 bytes at a time after some threshold?
+        // Maybe after seeing a few in a row that are ASCII, go back to fast mode?
+        int byte1 = 0;
+        for (; remaining > 0 && (byte1 = UNSAFE.getByte(address++)) >= 0; --remaining) {
+        }
+        if (remaining == 0) {
+          return COMPLETE;
+        }
+        remaining--;
+
+        if (byte1 < (byte) 0xE0) {
+          // Two-byte form
+
+          if (remaining == 0) {
+            // Incomplete sequence
+            return byte1;
+          }
+          remaining--;
+
+          // Simultaneously checks for illegal trailing-byte in
+          // leading position and overlong 2-byte form.
+          if (byte1 < (byte) 0xC2 || UNSAFE.getByte(address++) > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        } else if (byte1 < (byte) 0xF0) {
+          // Three-byte form
+
+          if (remaining < 2) {
+            // Incomplete sequence
+            return unsafeIncompleteStateFor(address, byte1, remaining);
+          }
+          remaining -= 2;
+
+          final byte byte2 = UNSAFE.getByte(address++);
+          if (byte2 > (byte) 0xBF
+              // overlong? 5 most significant bits must not all be zero
+              || (byte1 == (byte) 0xE0 && byte2 < (byte) 0xA0)
+              // check for illegal surrogate codepoints
+              || (byte1 == (byte) 0xED && byte2 >= (byte) 0xA0)
+              // byte3 trailing-byte test
+              || UNSAFE.getByte(address++) > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        } else {
+          // Four-byte form
+
+          if (remaining < 3) {
+            // Incomplete sequence
+            return unsafeIncompleteStateFor(address, byte1, remaining);
+          }
+          remaining -= 3;
+
+          final byte byte2 = UNSAFE.getByte(address++);
+          if (byte2 > (byte) 0xBF
+              // Check that 1 <= plane <= 16.  Tricky optimized form of:
+              // if (byte1 > (byte) 0xF4 ||
+              //     byte1 == (byte) 0xF0 && byte2 < (byte) 0x90 ||
+              //     byte1 == (byte) 0xF4 && byte2 > (byte) 0x8F)
+              || (((byte1 << 28) + (byte2 - (byte) 0x90)) >> 30) != 0
+              // byte3 trailing-byte test
+              || UNSAFE.getByte(address++) > (byte) 0xBF
+              // byte4 trailing-byte test
+              || UNSAFE.getByte(address++) > (byte) 0xBF) {
+            return MALFORMED;
+          }
+        }
+      }
+    }
+
+    private static int unsafeIncompleteStateFor(byte[] bytes, int byte1, long offset,
+        int remaining) {
+      switch (remaining) {
+        case 0: {
+          return incompleteStateFor(byte1);
+        }
+        case 1: {
+          return incompleteStateFor(byte1, UNSAFE.getByte(bytes, offset));
+        }
+        case 2: {
+          return incompleteStateFor(byte1, UNSAFE.getByte(bytes, offset),
+              UNSAFE.getByte(bytes, offset + 1));
+        }
+        default: {
+          throw new AssertionError();
+        }
+      }
+    }
+
+    private static int unsafeIncompleteStateFor(long address, final int byte1, int remaining) {
+      switch (remaining) {
+        case 0: {
+          return incompleteStateFor(byte1);
+        }
+        case 1: {
+          return incompleteStateFor(byte1, UNSAFE.getByte(address));
+        }
+        case 2: {
+          return incompleteStateFor(byte1, UNSAFE.getByte(address), UNSAFE.getByte(address + 1));
+        }
+        default: {
+          throw new AssertionError();
+        }
+      }
+    }
+
+    /**
+     * Gets the field with the given name within the class, or {@code null} if not found. If
+     * found, the field is made accessible.
+     */
+    private static Field field(Class<?> clazz, String fieldName) {
+      Field field;
+      try {
+        field = clazz.getDeclaredField(fieldName);
+        field.setAccessible(true);
+      } catch (Throwable t) {
+        // Failed to access the fields.
+        field = null;
+      }
+      logger.log(Level.FINEST, "{0}.{1}: {2}",
+          new Object[] {clazz.getName(), fieldName, (field != null ? "available" : "unavailable")});
+      return field;
+    }
+
+    /**
+     * Returns the offset of the provided field, or {@code -1} if {@code sun.misc.Unsafe} is not
+     * available.
+     */
+    private static long fieldOffset(Field field) {
+      return field == null || UNSAFE == null ? -1 : UNSAFE.objectFieldOffset(field);
+    }
+
+    /**
+     * Get the base offset for byte arrays, or {@code -1} if {@code sun.misc.Unsafe} is not
+     * available.
+     */
+    private static <T> int byteArrayBaseOffset() {
+      return UNSAFE == null ? -1 : UNSAFE.arrayBaseOffset(byte[].class);
+    }
+
+    /**
+     * Gets the offset of the {@code address} field of the given direct {@link ByteBuffer}.
+     */
+    private static long addressOffset(ByteBuffer buffer) {
+      return UNSAFE.getLong(buffer, BUFFER_ADDRESS_OFFSET);
+    }
+
+    /**
+     * Gets the {@code sun.misc.Unsafe} instance, or {@code null} if not available on this
+     * platform.
+     */
+    private static sun.misc.Unsafe getUnsafe() {
+      sun.misc.Unsafe unsafe = null;
+      try {
+        unsafe = AccessController.doPrivileged(new PrivilegedExceptionAction<sun.misc.Unsafe>() {
+          @Override
+          public sun.misc.Unsafe run() throws Exception {
+            Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;
+
+            // Check that this platform supports all of the required unsafe methods.
+            checkRequiredMethods(k);
+
+            for (Field f : k.getDeclaredFields()) {
+              f.setAccessible(true);
+              Object x = f.get(null);
+              if (k.isInstance(x)) {
+                return k.cast(x);
+              }
+            }
+            // The sun.misc.Unsafe field does not exist.
+            return null;
+          }
+        });
+      } catch (Throwable e) {
+        // Catching Throwable here due to the fact that Google AppEngine raises NoClassDefFoundError
+        // for Unsafe.
+      }
+
+      logger.log(Level.FINEST, "sun.misc.Unsafe: {}",
+          unsafe != null ? "available" : "unavailable");
+      return unsafe;
+    }
+
+    /**
+     * Verifies that all required methods of {@code sun.misc.Unsafe} are available on this platform.
+     */
+    private static void checkRequiredMethods(Class<sun.misc.Unsafe> clazz)
+        throws NoSuchMethodException, SecurityException {
+      // Needed for Unsafe byte[] access
+      clazz.getMethod("arrayBaseOffset", Class.class);
+      clazz.getMethod("getByte", Object.class, long.class);
+      clazz.getMethod("putByte", Object.class, long.class, byte.class);
+      clazz.getMethod("getLong", Object.class, long.class);
+
+      // Needed for Unsafe Direct ByteBuffer access
+      clazz.getMethod("objectFieldOffset", Field.class);
+      clazz.getMethod("getByte", long.class);
+      clazz.getMethod("getLong", Object.class, long.class);
+      clazz.getMethod("putByte", long.class, byte.class);
+      clazz.getMethod("getLong", long.class);
+    }
+  }
+
+  private Utf8() {}
 }