/*
    * Copyright (C) 2011 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.GwtCompatible;
  
  import java.math.BigInteger;
  import java.util.Arrays;
  import java.util.Comparator;
  
  /**
   * Static utility methods pertaining to {@code long} primitives that interpret values as
   * <i>unsigned</i> (that is, any negative value {@code x} is treated as the positive value
   * {@code 2^64 + x}). The methods for which signedness is not an issue are in {@link Longs}, as
   * well as signed versions of methods for which signedness is an issue.
   *
   * <p>In addition, this class provides several static methods for converting a {@code long} to a
   * {@code String} and a {@code String} to a {@code long} that treat the {@code long} as an unsigned
   * number.
   *
   * <p>Users of these utilities must be <i>extremely careful</i> not to mix up signed and unsigned
   * {@code long} values. When possible, it is recommended that the {@link UnsignedLong} wrapper
   * class be used, at a small efficiency penalty, to enforce the distinction in the type system.
   *
   * <p>See the Guava User Guide article on <a href=
   * "http://code.google.com/p/guava-libraries/wiki/PrimitivesExplained#Unsigned_support">
   * unsigned primitive utilities</a>.
   *
   * @author Louis Wasserman
   * @author Brian Milch
   * @author Colin Evans
   * @since 10.0
   */
  @Beta
  @GwtCompatible
  public final class UnsignedLongs {
    private UnsignedLongs() {}
  
    public static final long MAX_VALUE = -1L; // Equivalent to 2^64 - 1
  
    /**
     * A (self-inverse) bijection which converts the ordering on unsigned longs to the ordering on
     * longs, that is, {@code a <= b} as unsigned longs if and only if {@code flip(a) <= flip(b)}
     * as signed longs.
     */
    private static long flip(long a) {
      return a ^ Long.MIN_VALUE;
    }
  
    /**
     * Compares the two specified {@code long} values, treating them as unsigned values between
     * {@code 0} and {@code 2^64 - 1} inclusive.
     *
     * @param a the first unsigned {@code long} to compare
     * @param b the second unsigned {@code long} 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(long a, long b) {
      return Longs.compare(flip(a), flip(b));
    }
  
    /**
     * Returns the least value present in {@code array}, treating values as unsigned.
     *
     * @param array a <i>nonempty</i> array of unsigned {@code long} values
     * @return the value present in {@code array} that is less than or equal to every other value in
     *         the array according to {@link #compare}
     * @throws IllegalArgumentException if {@code array} is empty
     */
    public static long min(long... array) {
      checkArgument(array.length > 0);
      long min = flip(array[0]);
      for (int i = 1; i < array.length; i++) {
        long next = flip(array[i]);
        if (next < min) {
          min = next;
        }
      }
      return flip(min);
    }
  
    /**
    * Returns the greatest value present in {@code array}, treating values as unsigned.
    *
    * @param array a <i>nonempty</i> array of unsigned {@code long} values
    * @return the value present in {@code array} that is greater than or equal to every other value
    *         in the array according to {@link #compare}
    * @throws IllegalArgumentException if {@code array} is empty
    */
   public static long max(long... array) {
     checkArgument(array.length > 0);
     long max = flip(array[0]);
     for (int i = 1; i < array.length; i++) {
       long next = flip(array[i]);
       if (next > max) {
         max = next;
       }
     }
     return flip(max);
   }
 
   /**
    * Returns a string containing the supplied unsigned {@code long} values separated by
    * {@code separator}. For example, {@code join("-", 1, 2, 3)} returns the string {@code "1-2-3"}.
    *
    * @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 unsigned {@code long} values, possibly empty
    */
   public static String join(String separator, long... 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 * 5);
     builder.append(toString(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 arrays of unsigned {@code long} values
    * lexicographically. That is, it compares, using {@link #compare(long, long)}), 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 [] < [1L] < [1L, 2L] < [2L] < [1L << 63]}.
    *
    * <p>The returned comparator is inconsistent with {@link Object#equals(Object)} (since arrays
    * support only identity equality), but it is consistent with
    * {@link Arrays#equals(long[], long[])}.
    *
    * @see <a href="http://en.wikipedia.org/wiki/Lexicographical_order">Lexicographical order
    *      article at Wikipedia</a>
    */
   public static Comparator<long[]> lexicographicalComparator() {
     return LexicographicalComparator.INSTANCE;
   }
 
   enum LexicographicalComparator implements Comparator<long[]> {
     INSTANCE;
 
     @Override
     public int compare(long[] left, long[] right) {
       int minLength = Math.min(left.length, right.length);
       for (int i = 0; i < minLength; i++) {
         if (left[i] != right[i]) {
           return UnsignedLongs.compare(left[i], right[i]);
         }
       }
       return left.length - right.length;
     }
   }
 
   /**
    * Returns dividend / divisor, where the dividend and divisor are treated as unsigned 64-bit
    * quantities.
    *
    * @param dividend the dividend (numerator)
    * @param divisor the divisor (denominator)
    * @throws ArithmeticException if divisor is 0
    */
   public static long divide(long dividend, long divisor) {
     if (divisor < 0) { // i.e., divisor >= 2^63:
       if (compare(dividend, divisor) < 0) {
         return 0; // dividend < divisor
       } else {
         return 1; // dividend >= divisor
       }
     }
 
     // Optimization - use signed division if dividend < 2^63
     if (dividend >= 0) {
       return dividend / divisor;
     }
 
     /*
      * Otherwise, approximate the quotient, check, and correct if necessary. Our approximation is
      * guaranteed to be either exact or one less than the correct value. This follows from fact
      * that floor(floor(x)/i) == floor(x/i) for any real x and integer i != 0. The proof is not
      * quite trivial.
      */
     long quotient = ((dividend >>> 1) / divisor) << 1;
     long rem = dividend - quotient * divisor;
     return quotient + (compare(rem, divisor) >= 0 ? 1 : 0);
   }
 
   /**
    * Returns dividend % divisor, where the dividend and divisor are treated as unsigned 64-bit
    * quantities.
    *
    * @param dividend the dividend (numerator)
    * @param divisor the divisor (denominator)
    * @throws ArithmeticException if divisor is 0
    * @since 11.0
    */
   public static long remainder(long dividend, long divisor) {
     if (divisor < 0) { // i.e., divisor >= 2^63:
       if (compare(dividend, divisor) < 0) {
         return dividend; // dividend < divisor
       } else {
         return dividend - divisor; // dividend >= divisor
       }
     }
 
     // Optimization - use signed modulus if dividend < 2^63
     if (dividend >= 0) {
       return dividend % divisor;
     }
 
     /*
      * Otherwise, approximate the quotient, check, and correct if necessary. Our approximation is
      * guaranteed to be either exact or one less than the correct value. This follows from fact
      * that floor(floor(x)/i) == floor(x/i) for any real x and integer i != 0. The proof is not
      * quite trivial.
      */
     long quotient = ((dividend >>> 1) / divisor) << 1;
     long rem = dividend - quotient * divisor;
     return rem - (compare(rem, divisor) >= 0 ? divisor : 0);
   }
 
   /**
    * Returns the unsigned {@code long} value represented by the given decimal string.
    *
    * @throws NumberFormatException if the string does not contain a valid unsigned {@code long}
    *         value
    * @throws NullPointerException if {@code s} is null 
    *         (in contrast to {@link Long#parseLong(String)})
    */
   public static long parseUnsignedLong(String s) {
     return parseUnsignedLong(s, 10);
   }
 
   /**
    * Returns the unsigned {@code long} value represented by the given string.
    *
    * Accepts a decimal, hexadecimal, or octal number given by specifying the following prefix:
    *
    * <ul>
    * <li>{@code 0x}<i>HexDigits</i>
    * <li>{@code 0X}<i>HexDigits</i>
    * <li>{@code #}<i>HexDigits</i>
    * <li>{@code 0}<i>OctalDigits</i>
    * </ul>
    *
    * @throws NumberFormatException if the string does not contain a valid unsigned {@code long}
    *         value
    * @since 13.0
    */
   public static long decode(String stringValue) {
     ParseRequest request = ParseRequest.fromString(stringValue);
 
     try {
       return parseUnsignedLong(request.rawValue, request.radix);
     } catch (NumberFormatException e) {
       NumberFormatException decodeException =
           new NumberFormatException("Error parsing value: " + stringValue);
       decodeException.initCause(e);
       throw decodeException;
     }
   }
 
   /**
    * Returns the unsigned {@code long} value represented by a string with the given radix.
    *
    * @param s the string containing the unsigned {@code long} representation to be parsed.
    * @param radix the radix to use while parsing {@code s}
    * @throws NumberFormatException if the string does not contain a valid unsigned {@code long}
    *         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 Long#parseLong(String)})
    */
   public static long parseUnsignedLong(String s, int radix) {
     checkNotNull(s);
     if (s.length() == 0) {
       throw new NumberFormatException("empty string");
     }
     if (radix < Character.MIN_RADIX || radix > Character.MAX_RADIX) {
       throw new NumberFormatException("illegal radix: " + radix);
     }
 
     int max_safe_pos = maxSafeDigits[radix] - 1;
     long value = 0;
     for (int pos = 0; pos < s.length(); pos++) {
       int digit = Character.digit(s.charAt(pos), radix);
       if (digit == -1) {
         throw new NumberFormatException(s);
       }
       if (pos > max_safe_pos && overflowInParse(value, digit, radix)) {
         throw new NumberFormatException("Too large for unsigned long: " + s);
       }
       value = (value * radix) + digit;
     }
 
     return value;
   }
 
   /**
    * Returns true if (current * radix) + digit is a number too large to be represented by an
    * unsigned long. This is useful for detecting overflow while parsing a string representation of
    * a number. Does not verify whether supplied radix is valid, passing an invalid radix will give
    * undefined results or an ArrayIndexOutOfBoundsException.
    */
   private static boolean overflowInParse(long current, int digit, int radix) {
     if (current >= 0) {
       if (current < maxValueDivs[radix]) {
         return false;
       }
       if (current > maxValueDivs[radix]) {
         return true;
       }
       // current == maxValueDivs[radix]
       return (digit > maxValueMods[radix]);
     }
 
     // current < 0: high bit is set
     return true;
   }
 
   /**
    * Returns a string representation of x, where x is treated as unsigned.
    */
   public static String toString(long 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}.
    */
   public static String toString(long 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);
     if (x == 0) {
       // Simply return "0"
       return "0";
     } else {
       char[] buf = new char[64];
       int i = buf.length;
       if (x < 0) {
         // Separate off the last digit using unsigned division. That will leave
         // a number that is nonnegative as a signed integer.
         long quotient = divide(x, radix);
         long rem = x - quotient * radix;
         buf[--i] = Character.forDigit((int) rem, radix);
         x = quotient;
       }
       // Simple modulo/division approach
       while (x > 0) {
         buf[--i] = Character.forDigit((int) (x % radix), radix);
         x /= radix;
       }
       // Generate string
       return new String(buf, i, buf.length - i);
     }
   }
 
   // calculated as 0xffffffffffffffff / radix
   private static final long[] maxValueDivs = new long[Character.MAX_RADIX + 1];
   private static final int[] maxValueMods = new int[Character.MAX_RADIX + 1];
   private static final int[] maxSafeDigits = new int[Character.MAX_RADIX + 1];
   static {
     BigInteger overflow = new BigInteger("10000000000000000", 16);
     for (int i = Character.MIN_RADIX; i <= Character.MAX_RADIX; i++) {
       maxValueDivs[i] = divide(MAX_VALUE, i);
       maxValueMods[i] = (int) remainder(MAX_VALUE, i);
       maxSafeDigits[i] = overflow.toString(i).length() - 1;
     }
   }
 }