Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You 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 org.apache.lucene.util; import java.math.BigInteger; import java.util.Arrays; /** * Helper APIs to encode numeric values as sortable bytes and vice-versa. * * <p> * To also index floating point numbers, this class supplies two methods to convert them * to integer values by changing their bit layout: {@link #doubleToSortableLong}, * {@link #floatToSortableInt}. You will have no precision loss by * converting floating point numbers to integers and back (only that the integer form * is not usable). Other data types like dates can easily converted to longs or ints (e.g. * date to long: {@link java.util.Date#getTime}). * * @lucene.internal */ public final class NumericUtils { private NumericUtils() { } // no instance! /** * Converts a <code>double</code> value to a sortable signed <code>long</code>. * The value is converted by getting their IEEE 754 floating-point "double format" * bit layout and then some bits are swapped, to be able to compare the result as long. * By this the precision is not reduced, but the value can easily used as a long. * The sort order (including {@link Double#NaN}) is defined by * {@link Double#compareTo}; {@code NaN} is greater than positive infinity. * @see #sortableLongToDouble */ public static long doubleToSortableLong(double value) { return sortableDoubleBits(Double.doubleToLongBits(value)); } /** * Converts a sortable <code>long</code> back to a <code>double</code>. * @see #doubleToSortableLong */ public static double sortableLongToDouble(long encoded) { return Double.longBitsToDouble(sortableDoubleBits(encoded)); } /** * Converts a <code>float</code> value to a sortable signed <code>int</code>. * The value is converted by getting their IEEE 754 floating-point "float format" * bit layout and then some bits are swapped, to be able to compare the result as int. * By this the precision is not reduced, but the value can easily used as an int. * The sort order (including {@link Float#NaN}) is defined by * {@link Float#compareTo}; {@code NaN} is greater than positive infinity. * @see #sortableIntToFloat */ public static int floatToSortableInt(float value) { return sortableFloatBits(Float.floatToIntBits(value)); } /** * Converts a sortable <code>int</code> back to a <code>float</code>. * @see #floatToSortableInt */ public static float sortableIntToFloat(int encoded) { return Float.intBitsToFloat(sortableFloatBits(encoded)); } /** Converts IEEE 754 representation of a double to sortable order (or back to the original) */ public static long sortableDoubleBits(long bits) { return bits ^ (bits >> 63) & 0x7fffffffffffffffL; } /** Converts IEEE 754 representation of a float to sortable order (or back to the original) */ public static int sortableFloatBits(int bits) { return bits ^ (bits >> 31) & 0x7fffffff; } /** Result = a - b, where a >= b, else {@code IllegalArgumentException} is thrown. */ public static void subtract(int bytesPerDim, int dim, byte[] a, byte[] b, byte[] result) { int start = dim * bytesPerDim; int end = start + bytesPerDim; int borrow = 0; for (int i = end - 1; i >= start; i--) { int diff = (a[i] & 0xff) - (b[i] & 0xff) - borrow; if (diff < 0) { diff += 256; borrow = 1; } else { borrow = 0; } result[i - start] = (byte) diff; } if (borrow != 0) { throw new IllegalArgumentException("a < b"); } } /** Result = a + b, where a and b are unsigned. If there is an overflow, {@code IllegalArgumentException} is thrown. */ public static void add(int bytesPerDim, int dim, byte[] a, byte[] b, byte[] result) { int start = dim * bytesPerDim; int end = start + bytesPerDim; int carry = 0; for (int i = end - 1; i >= start; i--) { int digitSum = (a[i] & 0xff) + (b[i] & 0xff) + carry; if (digitSum > 255) { digitSum -= 256; carry = 1; } else { carry = 0; } result[i - start] = (byte) digitSum; } if (carry != 0) { throw new IllegalArgumentException("a + b overflows bytesPerDim=" + bytesPerDim); } } /** * Encodes an integer {@code value} such that unsigned byte order comparison * is consistent with {@link Integer#compare(int, int)} * @see #sortableBytesToInt(byte[], int) */ public static void intToSortableBytes(int value, byte[] result, int offset) { // Flip the sign bit, so negative ints sort before positive ints correctly: value ^= 0x80000000; result[offset] = (byte) (value >> 24); result[offset + 1] = (byte) (value >> 16); result[offset + 2] = (byte) (value >> 8); result[offset + 3] = (byte) value; } /** * Decodes an integer value previously written with {@link #intToSortableBytes} * @see #intToSortableBytes(int, byte[], int) */ public static int sortableBytesToInt(byte[] encoded, int offset) { int x = ((encoded[offset] & 0xFF) << 24) | ((encoded[offset + 1] & 0xFF) << 16) | ((encoded[offset + 2] & 0xFF) << 8) | (encoded[offset + 3] & 0xFF); // Re-flip the sign bit to restore the original value: return x ^ 0x80000000; } /** * Encodes an long {@code value} such that unsigned byte order comparison * is consistent with {@link Long#compare(long, long)} * @see #sortableBytesToLong(byte[], int) */ public static void longToSortableBytes(long value, byte[] result, int offset) { // Flip the sign bit so negative longs sort before positive longs: value ^= 0x8000000000000000L; result[offset] = (byte) (value >> 56); result[offset + 1] = (byte) (value >> 48); result[offset + 2] = (byte) (value >> 40); result[offset + 3] = (byte) (value >> 32); result[offset + 4] = (byte) (value >> 24); result[offset + 5] = (byte) (value >> 16); result[offset + 6] = (byte) (value >> 8); result[offset + 7] = (byte) value; } /** * Decodes a long value previously written with {@link #longToSortableBytes} * @see #longToSortableBytes(long, byte[], int) */ public static long sortableBytesToLong(byte[] encoded, int offset) { long v = ((encoded[offset] & 0xFFL) << 56) | ((encoded[offset + 1] & 0xFFL) << 48) | ((encoded[offset + 2] & 0xFFL) << 40) | ((encoded[offset + 3] & 0xFFL) << 32) | ((encoded[offset + 4] & 0xFFL) << 24) | ((encoded[offset + 5] & 0xFFL) << 16) | ((encoded[offset + 6] & 0xFFL) << 8) | (encoded[offset + 7] & 0xFFL); // Flip the sign bit back v ^= 0x8000000000000000L; return v; } /** * Encodes a BigInteger {@code value} such that unsigned byte order comparison * is consistent with {@link BigInteger#compareTo(BigInteger)}. This also sign-extends * the value to {@code bigIntSize} bytes if necessary: useful to create a fixed-width size. * @see #sortableBytesToBigInt(byte[], int, int) */ public static void bigIntToSortableBytes(BigInteger bigInt, int bigIntSize, byte[] result, int offset) { byte[] bigIntBytes = bigInt.toByteArray(); byte[] fullBigIntBytes; if (bigIntBytes.length < bigIntSize) { fullBigIntBytes = new byte[bigIntSize]; System.arraycopy(bigIntBytes, 0, fullBigIntBytes, bigIntSize - bigIntBytes.length, bigIntBytes.length); if ((bigIntBytes[0] & 0x80) != 0) { // sign extend Arrays.fill(fullBigIntBytes, 0, bigIntSize - bigIntBytes.length, (byte) 0xff); } } else if (bigIntBytes.length == bigIntSize) { fullBigIntBytes = bigIntBytes; } else { throw new IllegalArgumentException( "BigInteger: " + bigInt + " requires more than " + bigIntSize + " bytes storage"); } // Flip the sign bit so negative bigints sort before positive bigints: fullBigIntBytes[0] ^= 0x80; System.arraycopy(fullBigIntBytes, 0, result, offset, bigIntSize); assert sortableBytesToBigInt(result, offset, bigIntSize).equals(bigInt) : "bigInt=" + bigInt + " converted=" + sortableBytesToBigInt(result, offset, bigIntSize); } /** * Decodes a BigInteger value previously written with {@link #bigIntToSortableBytes} * @see #bigIntToSortableBytes(BigInteger, int, byte[], int) */ public static BigInteger sortableBytesToBigInt(byte[] encoded, int offset, int length) { byte[] bigIntBytes = new byte[length]; System.arraycopy(encoded, offset, bigIntBytes, 0, length); // Flip the sign bit back to the original bigIntBytes[0] ^= 0x80; return new BigInteger(bigIntBytes); } }