/*
    * Copyright (C) 2009 The Guava Authors
    *
    * Licensed under the Apache License, Version 2.0 (the "License");
    * you may not use this file except in compliance with the License.
    * You may obtain a copy of the License at
    *
    * http://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package com.google.common.primitives;
  
  import static com.google.common.base.Preconditions.checkArgument;
  import static com.google.common.base.Preconditions.checkNotNull;
  
  import com.google.common.annotations.Beta;
  import com.google.common.annotations.VisibleForTesting;
  
  import sun.misc.Unsafe;
  
  import java.nio.ByteOrder;
  import java.util.Comparator;
  
  /**
   * Static utility methods pertaining to {@code byte} primitives that interpret
   * values as <i>unsigned</i> (that is, any negative value {@code b} is treated
   * as the positive value {@code 256 + b}). The corresponding methods that treat
   * the values as signed are found in {@link SignedBytes}, and the methods for
   * which signedness is not an issue are in {@link Bytes}.
   *
   * <p>See the Guava User Guide article on <a href=
   * "http://code.google.com/p/guava-libraries/wiki/PrimitivesExplained">
   * primitive utilities</a>.
   *
   * @author Kevin Bourrillion
   * @author Martin Buchholz
   * @author Hiroshi Yamauchi
   * @author Louis Wasserman
   * @since 1.0
   */
  public final class UnsignedBytes {
    private UnsignedBytes() {}
  
    /**
     * The largest power of two that can be represented as an unsigned {@code
     * byte}.
     *
     * @since 10.0
     */
    public static final byte MAX_POWER_OF_TWO = (byte) 0x80;
  
    /**
     * The largest value that fits into an unsigned byte.
     *
     * @since 13.0
     */
    public static final byte MAX_VALUE = (byte) 0xFF;
  
    private static final int UNSIGNED_MASK = 0xFF;
  
    /**
     * Returns the value of the given byte as an integer, when treated as
     * unsigned. That is, returns {@code value + 256} if {@code value} is
     * negative; {@code value} itself otherwise.
     *
     * @since 6.0
     */
    public static int toInt(byte value) {
      return value & UNSIGNED_MASK;
    }
  
    /**
     * Returns the {@code byte} value that, when treated as unsigned, is equal to
     * {@code value}, if possible.
     *
     * @param value a value between 0 and 255 inclusive
     * @return the {@code byte} value that, when treated as unsigned, equals
     *     {@code value}
     * @throws IllegalArgumentException if {@code value} is negative or greater
     *     than 255
     */
    public static byte checkedCast(long value) {
      if ((value >> Byte.SIZE) != 0) {
        // don't use checkArgument here, to avoid boxing
        throw new IllegalArgumentException("Out of range: " + value);
      }
      return (byte) value;
    }
  
    /**
     * Returns the {@code byte} value that, when treated as unsigned, is nearest
     * in value to {@code value}.
     *
    * @param value any {@code long} value
    * @return {@code (byte) 255} if {@code value >= 255}, {@code (byte) 0} if
    *     {@code value <= 0}, and {@code value} cast to {@code byte} otherwise
    */
   public static byte saturatedCast(long value) {
     if (value > toInt(MAX_VALUE)) {
       return MAX_VALUE; // -1
     }
     if (value < 0) {
       return (byte) 0;
     }
     return (byte) value;
   }
 
   /**
    * Compares the two specified {@code byte} values, treating them as unsigned
    * values between 0 and 255 inclusive. For example, {@code (byte) -127} is
    * considered greater than {@code (byte) 127} because it is seen as having
    * the value of positive {@code 129}.
    *
    * @param a the first {@code byte} to compare
    * @param b the second {@code byte} to compare
    * @return a negative value if {@code a} is less than {@code b}; a positive
    *     value if {@code a} is greater than {@code b}; or zero if they are equal
    */
   public static int compare(byte a, byte b) {
     return toInt(a) - toInt(b);
   }
 
   /**
    * Returns the least value present in {@code array}.
    *
    * @param array a <i>nonempty</i> array of {@code byte} values
    * @return the value present in {@code array} that is less than or equal to
    *     every other value in the array
    * @throws IllegalArgumentException if {@code array} is empty
    */
   public static byte min(byte... array) {
     checkArgument(array.length > 0);
     int min = toInt(array[0]);
     for (int i = 1; i < array.length; i++) {
       int next = toInt(array[i]);
       if (next < min) {
         min = next;
       }
     }
     return (byte) min;
   }
 
   /**
    * Returns the greatest value present in {@code array}.
    *
    * @param array a <i>nonempty</i> array of {@code byte} values
    * @return the value present in {@code array} that is greater than or equal
    *     to every other value in the array
    * @throws IllegalArgumentException if {@code array} is empty
    */
   public static byte max(byte... array) {
     checkArgument(array.length > 0);
     int max = toInt(array[0]);
     for (int i = 1; i < array.length; i++) {
       int next = toInt(array[i]);
       if (next > max) {
         max = next;
       }
     }
     return (byte) max;
   }
 
   /**
    * Returns a string representation of x, where x is treated as unsigned.
    *
    * @since 13.0
    */
   @Beta
   public static String toString(byte x) {
     return toString(x, 10);
   }
 
   /**
    * Returns a string representation of {@code x} for the given radix, where {@code x} is treated
    * as unsigned.
    *
    * @param x the value to convert to a string.
    * @param radix the radix to use while working with {@code x}
    * @throws IllegalArgumentException if {@code radix} is not between {@link Character#MIN_RADIX}
    *         and {@link Character#MAX_RADIX}.
    * @since 13.0
    */
   @Beta
   public static String toString(byte x, int radix) {
     checkArgument(radix >= Character.MIN_RADIX && radix <= Character.MAX_RADIX,
         "radix (%s) must be between Character.MIN_RADIX and Character.MAX_RADIX", radix);
     // Benchmarks indicate this is probably not worth optimizing.
     return Integer.toString(toInt(x), radix);
   }
 
   /**
    * Returns the unsigned {@code byte} value represented by the given decimal string.
    *
    * @throws NumberFormatException if the string does not contain a valid unsigned {@code byte}
    *         value
    * @throws NullPointerException if {@code s} is null 
    *         (in contrast to {@link Byte#parseByte(String)})
    * @since 13.0
    */
   @Beta
   public static byte parseUnsignedByte(String string) {
     return parseUnsignedByte(string, 10);
   }
 
   /**
    * Returns the unsigned {@code byte} value represented by a string with the given radix.
    *
    * @param string the string containing the unsigned {@code byte} representation to be parsed.
    * @param radix the radix to use while parsing {@code string}
    * @throws NumberFormatException if the string does not contain a valid unsigned {@code byte}
    *         with the given radix, or if {@code radix} is not between {@link Character#MIN_RADIX}
    *         and {@link Character#MAX_RADIX}.
    * @throws NullPointerException if {@code s} is null 
    *         (in contrast to {@link Byte#parseByte(String)})
    * @since 13.0
    */
   @Beta
   public static byte parseUnsignedByte(String string, int radix) {
     int parse = Integer.parseInt(checkNotNull(string), radix);
     // We need to throw a NumberFormatException, so we have to duplicate checkedCast. =(
     if (parse >> Byte.SIZE == 0) {
       return (byte) parse;
     } else {
       throw new NumberFormatException("out of range: " + parse);
     }
   }
 
   /**
    * Returns a string containing the supplied {@code byte} values separated by
    * {@code separator}. For example, {@code join(":", (byte) 1, (byte) 2,
    * (byte) 255)} returns the string {@code "1:2:255"}.
    *
    * @param separator the text that should appear between consecutive values in
    *     the resulting string (but not at the start or end)
    * @param array an array of {@code byte} values, possibly empty
    */
   public static String join(String separator, byte... array) {
     checkNotNull(separator);
     if (array.length == 0) {
       return "";
     }
 
     // For pre-sizing a builder, just get the right order of magnitude
     StringBuilder builder = new StringBuilder(array.length * (3 + separator.length()));
     builder.append(toInt(array[0]));
     for (int i = 1; i < array.length; i++) {
       builder.append(separator).append(toString(array[i]));
     }
     return builder.toString();
   }
 
   /**
    * Returns a comparator that compares two {@code byte} arrays
    * lexicographically. That is, it compares, using {@link
    * #compare(byte, byte)}), the first pair of values that follow any common
    * prefix, or when one array is a prefix of the other, treats the shorter
    * array as the lesser. For example, {@code [] < [0x01] < [0x01, 0x7F] <
    * [0x01, 0x80] < [0x02]}. Values are treated as unsigned.
    *
    * <p>The returned comparator is inconsistent with {@link
    * Object#equals(Object)} (since arrays support only identity equality), but
    * it is consistent with {@link java.util.Arrays#equals(byte[], byte[])}.
    *
    * @see <a href="http://en.wikipedia.org/wiki/Lexicographical_order">
    *     Lexicographical order article at Wikipedia</a>
    * @since 2.0
    */
   public static Comparator<byte[]> lexicographicalComparator() {
     return LexicographicalComparatorHolder.BEST_COMPARATOR;
   }
 
   @VisibleForTesting
   static Comparator<byte[]> lexicographicalComparatorJavaImpl() {
     return LexicographicalComparatorHolder.PureJavaComparator.INSTANCE;
   }
 
   /**
    * Provides a lexicographical comparator implementation; either a Java
    * implementation or a faster implementation based on {@link Unsafe}.
    *
    * <p>Uses reflection to gracefully fall back to the Java implementation if
    * {@code Unsafe} isn't available.
    */
   @VisibleForTesting
   static class LexicographicalComparatorHolder {
     static final String UNSAFE_COMPARATOR_NAME =
         LexicographicalComparatorHolder.class.getName() + "$UnsafeComparator";
 
     static final Comparator<byte[]> BEST_COMPARATOR = getBestComparator();
 
     @VisibleForTesting
     enum UnsafeComparator implements Comparator<byte[]> {
       INSTANCE;
 
       static final boolean BIG_ENDIAN =
           ByteOrder.nativeOrder().equals(ByteOrder.BIG_ENDIAN);
 
       /*
        * The following static final fields exist for performance reasons.
        *
        * In UnsignedBytesBenchmark, accessing the following objects via static
        * final fields is the fastest (more than twice as fast as the Java
        * implementation, vs ~1.5x with non-final static fields, on x86_32)
        * under the Hotspot server compiler. The reason is obviously that the
        * non-final fields need to be reloaded inside the loop.
        *
        * And, no, defining (final or not) local variables out of the loop still
        * isn't as good because the null check on the theUnsafe object remains
        * inside the loop and BYTE_ARRAY_BASE_OFFSET doesn't get
        * constant-folded.
        *
        * The compiler can treat static final fields as compile-time constants
        * and can constant-fold them while (final or not) local variables are
        * run time values.
        */
 
       static final Unsafe theUnsafe;
 
       /** The offset to the first element in a byte array. */
       static final int BYTE_ARRAY_BASE_OFFSET;
 
       static {
         theUnsafe = getUnsafe();
 
         BYTE_ARRAY_BASE_OFFSET = theUnsafe.arrayBaseOffset(byte[].class);
 
         // sanity check - this should never fail
         if (theUnsafe.arrayIndexScale(byte[].class) != 1) {
           throw new AssertionError();
         }
       }
       
       /**
        * Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
        * Replace with a simple call to Unsafe.getUnsafe when integrating
        * into a jdk.
        *
        * @return a sun.misc.Unsafe
        */
       private static sun.misc.Unsafe getUnsafe() {
           try {
               return sun.misc.Unsafe.getUnsafe();
           } catch (SecurityException tryReflectionInstead) {}
           try {
               return java.security.AccessController.doPrivileged
               (new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
                   public sun.misc.Unsafe run() throws Exception {
                       Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;
                       for (java.lang.reflect.Field f : k.getDeclaredFields()) {
                           f.setAccessible(true);
                           Object x = f.get(null);
                           if (k.isInstance(x))
                               return k.cast(x);
                       }
                       throw new NoSuchFieldError("the Unsafe");
                   }});
           } catch (java.security.PrivilegedActionException e) {
               throw new RuntimeException("Could not initialize intrinsics",
                                          e.getCause());
           }
       }
 
       @Override public int compare(byte[] left, byte[] right) {
         int minLength = Math.min(left.length, right.length);
         int minWords = minLength / Longs.BYTES;
 
         /*
          * Compare 8 bytes at a time. Benchmarking shows comparing 8 bytes at a
          * time is no slower than comparing 4 bytes at a time even on 32-bit.
          * On the other hand, it is substantially faster on 64-bit.
          */
         for (int i = 0; i < minWords * Longs.BYTES; i += Longs.BYTES) {
           long lw = theUnsafe.getLong(left, BYTE_ARRAY_BASE_OFFSET + (long) i);
           long rw = theUnsafe.getLong(right, BYTE_ARRAY_BASE_OFFSET + (long) i);
           if (lw != rw) {
             if (BIG_ENDIAN) {
               return UnsignedLongs.compare(lw, rw);
             }
 
             /*
              * We want to compare only the first index where left[index] != right[index].
              * This corresponds to the least significant nonzero byte in lw ^ rw, since lw
              * and rw are little-endian.  Long.numberOfTrailingZeros(diff) tells us the least 
              * significant nonzero bit, and zeroing out the first three bits of L.nTZ gives us the 
              * shift to get that least significant nonzero byte.
              */
             int n = Long.numberOfTrailingZeros(lw ^ rw) & ~0x7;
             return (int) (((lw >>> n) & UNSIGNED_MASK) - ((rw >>> n) & UNSIGNED_MASK));
           }
         }
 
         // The epilogue to cover the last (minLength % 8) elements.
         for (int i = minWords * Longs.BYTES; i < minLength; i++) {
           int result = UnsignedBytes.compare(left[i], right[i]);
           if (result != 0) {
             return result;
           }
         }
         return left.length - right.length;
       }
     }
 
     enum PureJavaComparator implements Comparator<byte[]> {
       INSTANCE;
 
       @Override public int compare(byte[] left, byte[] right) {
         int minLength = Math.min(left.length, right.length);
         for (int i = 0; i < minLength; i++) {
           int result = UnsignedBytes.compare(left[i], right[i]);
           if (result != 0) {
             return result;
           }
         }
         return left.length - right.length;
       }
     }
 
     /**
      * Returns the Unsafe-using Comparator, or falls back to the pure-Java
      * implementation if unable to do so.
      */
     static Comparator<byte[]> getBestComparator() {
       try {
         Class<?> theClass = Class.forName(UNSAFE_COMPARATOR_NAME);
 
         // yes, UnsafeComparator does implement Comparator<byte[]>
         @SuppressWarnings("unchecked")
         Comparator<byte[]> comparator =
             (Comparator<byte[]>) theClass.getEnumConstants()[0];
         return comparator;
       } catch (Throwable t) { // ensure we really catch *everything*
         return lexicographicalComparatorJavaImpl();
       }
     }
   }
 }