Java tutorial
/* * 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; import javax.annotation.CheckReturnValue; /** * 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= * "https://github.com/google/guava/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 */ @CheckReturnValue 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 */ @CheckReturnValue 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 */ @CheckReturnValue 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 */ @CheckReturnValue 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> */ @CheckReturnValue 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 */ @CheckReturnValue 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 */ @CheckReturnValue 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. */ @CheckReturnValue 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}. */ @CheckReturnValue 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; } } }