/**
* 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.mahout.math;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import com.google.common.base.Preconditions;
/**
* <p>Encodes signed and unsigned values using a common variable-length
* scheme, found for example in
* <a href="http://code.google.com/apis/protocolbuffers/docs/encoding.html">
* Google's Protocol Buffers</a>. It uses fewer bytes to encode smaller values,
* but will use slightly more bytes to encode large values.</p>
*
* <p>Signed values are further encoded using so-called zig-zag encoding
* in order to make them "compatible" with variable-length encoding.</p>
*/
public final class Varint {
private Varint() {
}
/**
* Encodes a value using the variable-length encoding from
* <a href="http://code.google.com/apis/protocolbuffers/docs/encoding.html">
* Google Protocol Buffers</a>. It uses zig-zag encoding to efficiently
* encode signed values. If values are known to be nonnegative,
* {@link #writeUnsignedVarLong(long, DataOutput)} should be used.
*
* @param value value to encode
* @param out to write bytes to
* @throws IOException if {@link DataOutput} throws {@link IOException}
*/
public static void writeSignedVarLong(long value, DataOutput out) throws IOException {
// Great trick from http://code.google.com/apis/protocolbuffers/docs/encoding.html#types
writeUnsignedVarLong((value << 1) ^ (value >> 63), out);
}
/**
* Encodes a value using the variable-length encoding from
* <a href="http://code.google.com/apis/protocolbuffers/docs/encoding.html">
* Google Protocol Buffers</a>. Zig-zag is not used, so input must not be negative.
* If values can be negative, use {@link #writeSignedVarLong(long, DataOutput)}
* instead. This method treats negative input as like a large unsigned value.
*
* @param value value to encode
* @param out to write bytes to
* @throws IOException if {@link DataOutput} throws {@link IOException}
*/
public static void writeUnsignedVarLong(long value, DataOutput out) throws IOException {
while ((value & 0xFFFFFFFFFFFFFF80L) != 0L) {
out.writeByte(((int) value & 0x7F) | 0x80);
value >>>= 7;
}
out.writeByte((int) value & 0x7F);
}
/**
* @see #writeSignedVarLong(long, DataOutput)
*/
public static void writeSignedVarInt(int value, DataOutput out) throws IOException {
// Great trick from http://code.google.com/apis/protocolbuffers/docs/encoding.html#types
writeUnsignedVarInt((value << 1) ^ (value >> 31), out);
}
/**
* @see #writeUnsignedVarLong(long, DataOutput)
*/
public static void writeUnsignedVarInt(int value, DataOutput out) throws IOException {
while ((value & 0xFFFFFF80) != 0L) {
out.writeByte((value & 0x7F) | 0x80);
value >>>= 7;
}
out.writeByte(value & 0x7F);
}
/**
* @param in to read bytes from
* @return decode value
* @throws IOException if {@link DataInput} throws {@link IOException}
* @throws IllegalArgumentException if variable-length value does not terminate
* after 9 bytes have been read
* @see #writeSignedVarLong(long, DataOutput)
*/
public static long readSignedVarLong(DataInput in) throws IOException {
long raw = readUnsignedVarLong(in);
// This undoes the trick in writeSignedVarLong()
long temp = (((raw << 63) >> 63) ^ raw) >> 1;
// This extra step lets us deal with the largest signed values by treating
// negative results from read unsigned methods as like unsigned values
// Must re-flip the top bit if the original read value had it set.
return temp ^ (raw & (1L << 63));
}
/**
* @param in to read bytes from
* @return decode value
* @throws IOException if {@link DataInput} throws {@link IOException}
* @throws IllegalArgumentException if variable-length value does not terminate
* after 9 bytes have been read
* @see #writeUnsignedVarLong(long, DataOutput)
*/
public static long readUnsignedVarLong(DataInput in) throws IOException {
long value = 0L;
int i = 0;
long b;
while (((b = in.readByte()) & 0x80L) != 0) {
value |= (b & 0x7F) << i;
i += 7;
Preconditions.checkArgument(i <= 63, "Variable length quantity is too long");
}
return value | (b << i);
}
/**
* @throws IllegalArgumentException if variable-length value does not terminate
* after 5 bytes have been read
* @throws IOException if {@link DataInput} throws {@link IOException}
* @see #readSignedVarLong(DataInput)
*/
public static int readSignedVarInt(DataInput in) throws IOException {
int raw = readUnsignedVarInt(in);
// This undoes the trick in writeSignedVarInt()
int temp = (((raw << 31) >> 31) ^ raw) >> 1;
// This extra step lets us deal with the largest signed values by treating
// negative results from read unsigned methods as like unsigned values.
// Must re-flip the top bit if the original read value had it set.
return temp ^ (raw & (1 << 31));
}
/**
* @throws IllegalArgumentException if variable-length value does not terminate
* after 5 bytes have been read
* @throws IOException if {@link DataInput} throws {@link IOException}
* @see #readUnsignedVarLong(DataInput)
*/
public static int readUnsignedVarInt(DataInput in) throws IOException {
int value = 0;
int i = 0;
int b;
while (((b = in.readByte()) & 0x80) != 0) {
value |= (b & 0x7F) << i;
i += 7;
Preconditions.checkArgument(i <= 35, "Variable length quantity is too long");
}
return value | (b << i);
}
}