--- /dev/null
+package org.apache.lucene.util;
+
+import java.io.EOFException;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+
+/**
+ * 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.
+ */
+
+/**
+ * Variable-length encoding of 32-bit integers, into 8-bit bytes. A number is encoded as follows:
+ * <ul>
+ * <li>If it is less than 127 and non-negative (i.e., if the number uses only 7 bits), it is encoded as
+ * as single byte: 0bbbbbbb.
+ * <li>If its highest nonzero bit is greater than bit 6 (0x40), it is represented as a series of
+ * bytes, each byte's
+ * 7 LSB containing bits from the original value, with the MSB set for all but the last
+ * byte. The first encoded byte contains the highest nonzero bits from the
+ * original; the second byte contains the next 7 MSB; and so on, with the last byte
+ * containing the 7 LSB of the original.
+ * </ul>
+ * Examples:
+ * <ol>
+ * <li>n = 117 = 1110101: This has fewer than 8 significant bits, and so is encoded as
+ * 01110101 = 0x75.
+ * <li>n = 100000 = (binary) 11000011010100000. This has 17 significant bits, and so needs
+ * three Vint8 bytes. Left-zero-pad it to a multiple of 7 bits, then split it into chunks of 7
+ * and add an MSB, 0 for the last byte, 1 for the others: 1|0000110 1|0001101 0|0100000
+ * = 0x86 0x8D 0x20.
+ * </ol>
+ * This encoder/decoder will correctly handle any 32-bit integer, but for negative numbers,
+ * and positive numbers with more than 28 significant bits, encoding requires 5 bytes; this
+ * is not an efficient encoding scheme for large
+ * positive numbers or any negative number.
+ * <p>
+ * <b>Compatibility:</b><br>
+ * This class has been used in products that have shipped to customers, and is needed to
+ * decode legacy data. Do not modify this class in ways that will break compatibility.
+ *
+ * @lucene.experimental
+ */
+public class Vint8 {
+
+ /**
+ * Because Java lacks call-by-reference, this class boxes the decoding position, which
+ * is initially set by the caller, and returned after decoding, incremented by the number
+ * of bytes processed.
+ */
+ public static class Position {
+ /**
+ * Creates a position value set to zero.
+ */
+ public Position() {
+ // The initial position is zero by default.
+ }
+ /**
+ * Creates a position set to {@code initialPosition}.
+ * @param initialPosition The starting decoding position in the source buffer.
+ */
+ public Position(int initialPosition) {
+ this.pos = initialPosition;
+ }
+ /**
+ * The value passed by reference.
+ */
+ public int pos;
+ }
+
+ /**
+ * Returns the number of bytes needed to encode {@code number}.
+ * @param number The number whose encoded length is needed.
+ * @return The number of bytes needed to encode {@code number}.
+ */
+ public static int bytesNeeded(int number) {
+ if ((number & ~0x7F) == 0) {
+ return 1;
+ } else if ((number & ~0x3FFF) == 0) {
+ return 2;
+ } else if ((number & ~0x1FFFFF) == 0) {
+ return 3;
+ } else if ((number & ~0xFFFFFFF) == 0) {
+ return 4;
+ } else {
+ return 5;
+ }
+ }
+
+ /**
+ * The maximum number of bytes needed to encode a number using {@code Vint8}.
+ */
+ public static final int MAXIMUM_BYTES_NEEDED = 5;
+
+ /**
+ * Encodes {@code number} to {@code out}.
+ * @param number The value to be written in encoded form, to {@code out}.
+ * @param out The output stream receiving the encoded bytes.
+ * @exception IOException If there is a problem writing to {@code out}.
+ */
+ public static void encode(int number, OutputStream out) throws IOException {
+ if ((number & ~0x7F) == 0) {
+ out.write(number);
+ } else if ((number & ~0x3FFF) == 0) {
+ out.write(0x80 | (number >> 7));
+ out.write(0x7F & number);
+ } else if ((number & ~0x1FFFFF) == 0) {
+ out.write(0x80 | (number >> 14));
+ out.write(0x80 | (number >> 7));
+ out.write(0x7F & number);
+ } else if ((number & ~0xFFFFFFF) == 0) {
+ out.write(0x80 | (number >> 21));
+ out.write(0x80 | (number >> 14));
+ out.write(0x80 | (number >> 7));
+ out.write(0x7F & number);
+ } else {
+ out.write(0x80 | (number >> 28));
+ out.write(0x80 | (number >> 21));
+ out.write(0x80 | (number >> 14));
+ out.write(0x80 | (number >> 7));
+ out.write(0x7F & number);
+ }
+ }
+
+ /**
+ * Encodes {@code number} into {@code dest}, starting at offset {@code start} from
+ * the beginning of the array. This method assumes {@code dest} is large enough to
+ * hold the required number of bytes.
+ * @param number The number to be encoded.
+ * @param dest The destination array.
+ * @param start The starting offset in the array.
+ * @return The number of bytes used in the array.
+ */
+ public static int encode(int number, byte[] dest, int start) {
+ if ((number & ~0x7F) == 0) {
+ dest[start] = (byte) number;
+ return 1;
+ } else if ((number & ~0x3FFF) == 0) {
+ dest[start] = (byte) (0x80 | ((number & 0x3F80) >> 7));
+ dest[start + 1] = (byte) (number & 0x7F);
+ return 2;
+ } else if ((number & ~0x1FFFFF) == 0) {
+ dest[start] = (byte) (0x80 | ((number & 0x1FC000) >> 14));
+ dest[start + 1] = (byte) (0x80 | ((number & 0x3F80) >> 7));
+ dest[start + 2] = (byte) (number & 0x7F);
+ return 3;
+ } else if ((number & ~0xFFFFFFF) == 0) {
+ dest[start] = (byte) (0x80 | ((number & 0xFE00000) >> 21));
+ dest[start + 1] = (byte) (0x80 | ((number & 0x1FC000) >> 14));
+ dest[start + 2] = (byte) (0x80 | ((number & 0x3F80) >> 7));
+ dest[start + 3] = (byte) (number & 0x7F);
+ return 4;
+ } else {
+ dest[start] = (byte) (0x80 | ((number & 0xF0000000) >> 28));
+ dest[start + 1] = (byte) (0x80 | ((number & 0xFE00000) >> 21));
+ dest[start + 2] = (byte) (0x80 | ((number & 0x1FC000) >> 14));
+ dest[start + 3] = (byte) (0x80 | ((number & 0x3F80) >> 7));
+ dest[start + 4] = (byte) (number & 0x7F);
+ return 5;
+ }
+ }
+
+ /**
+ * Decodes a 32-bit integer from {@code bytes}, beginning at offset {@code pos.pos}.
+ * The decoded value is returned, and {@code pos.pos} is incremented by the number of
+ * bytes processed.
+ * @param bytes The byte array containing an encoded value.
+ * @param pos On entry, the starting position in the array; on return, one greater
+ * than the position of the last byte decoded in the call.
+ * @return The decoded value.
+ */
+ public static int decode(byte[] bytes, Position pos) {
+ int value = 0;
+ while (true) {
+ byte first = bytes[pos.pos];
+ ++pos.pos;
+ value |= first & 0x7F;
+ if ((first & 0x80) == 0) {
+ return value;
+ }
+ value <<= 7;
+ }
+ }
+
+ /**
+ * Decodes a 32-bit integer from bytes read from {@code in}. Bytes are read,
+ * one at a time, from {@code in}, and it is assumed they represent a 32-bit
+ * integer encoded using this class's encoding scheme. The decoded value is
+ * returned.
+ * @param in The input stream containing the encoded bytes.
+ * @return The decoded value.
+ * @exception EOFException If the stream ends before a value has been decoded.
+ */
+ public static int decode(InputStream in) throws IOException {
+ int value = 0;
+ while (true) {
+ int first = in.read();
+ if (first < 0) {
+ throw new EOFException();
+ }
+ value |= first & 0x7F;
+ if ((first & 0x80) == 0) {
+ return value;
+ }
+ value <<= 7;
+ }
+ }
+
+ /**
+ * The default ctor is made private because all methods of this class are static.
+ */
+ private Vint8() {
+ // Just making it impossible to instantiate.
+ }
+
+}
fnp / pylucene.git / blobdiff