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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
/*
* Licensed to the Apache Software Foundation (ASF) under one
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*
* http://www.apache.org/licenses/LICENSE-2.0
*
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* 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.
*/
// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc. All rights reserved.
// https://developers.google.com/protocol-buffers/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
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// in the documentation and/or other materials provided with the
// distribution.
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// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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package org.apache.cassandra.utils.vint;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.nio.ByteBuffer;
import io.netty.util.concurrent.FastThreadLocal;
import net.nicoulaj.compilecommand.annotations.Inline;
/**
* Borrows idea from
* https://developers.google.com/protocol-buffers/docs/encoding#varints
*/
public class VIntCoding
{
public static long readUnsignedVInt(DataInput input) throws IOException
{
int firstByte = input.readByte();
//Bail out early if this is one byte, necessary or it fails later
if (firstByte >= 0)
return firstByte;
int size = numberOfExtraBytesToRead(firstByte);
long retval = firstByte & firstByteValueMask(size);
for (int ii = 0; ii < size; ii++)
{
byte b = input.readByte();
retval <<= 8;
retval |= b & 0xff;
}
return retval;
}
/**
* Note this method is the same as {@link #readUnsignedVInt(DataInput)},
* except that we do *not* block if there are not enough bytes in the buffer
* to reconstruct the value.
*
* WARNING: this method is only safe for vints we know to be representable by a positive long value.
*
* @return -1 if there are not enough bytes in the input to read the value; else, the vint unsigned value.
*/
public static long getUnsignedVInt(ByteBuffer input, int readerIndex)
{
return getUnsignedVInt(input, readerIndex, input.limit());
}
public static long getUnsignedVInt(ByteBuffer input, int readerIndex, int readerLimit)
{
if (readerIndex >= readerLimit)
return -1;
int firstByte = input.get(readerIndex++);
//Bail out early if this is one byte, necessary or it fails later
if (firstByte >= 0)
return firstByte;
int size = numberOfExtraBytesToRead(firstByte);
if (readerIndex + size > readerLimit)
return -1;
long retval = firstByte & firstByteValueMask(size);
for (int ii = 0; ii < size; ii++)
{
byte b = input.get(readerIndex++);
retval <<= 8;
retval |= b & 0xff;
}
return retval;
}
public static long readVInt(DataInput input) throws IOException
{
return decodeZigZag64(readUnsignedVInt(input));
}
// & this with the first byte to give the value part for a given extraBytesToRead encoded in the byte
public static int firstByteValueMask(int extraBytesToRead)
{
// by including the known 0bit in the mask, we can use this for encodeExtraBytesToRead
return 0xff >> extraBytesToRead;
}
public static int encodeExtraBytesToRead(int extraBytesToRead)
{
// because we have an extra bit in the value mask, we just need to invert it
return ~firstByteValueMask(extraBytesToRead);
}
public static int numberOfExtraBytesToRead(int firstByte)
{
// we count number of set upper bits; so if we simply invert all of the bits, we're golden
// this is aided by the fact that we only work with negative numbers, so when upcast to an int all
// of the new upper bits are also set, so by inverting we set all of them to zero
return Integer.numberOfLeadingZeros(~firstByte) - 24;
}
protected static final FastThreadLocal encodingBuffer = new FastThreadLocal()
{
@Override
public byte[] initialValue()
{
return new byte[9];
}
};
public static void writeUnsignedVInt(long value, DataOutput output) throws IOException
{
int size = VIntCoding.computeUnsignedVIntSize(value);
if (size == 1)
{
output.write((int)value);
return;
}
output.write(VIntCoding.encodeVInt(value, size), 0, size);
}
@Inline
public static byte[] encodeVInt(long value, int size)
{
byte encodingSpace[] = encodingBuffer.get();
int extraBytes = size - 1;
for (int i = extraBytes ; i >= 0; --i)
{
encodingSpace[i] = (byte) value;
value >>= 8;
}
encodingSpace[0] |= VIntCoding.encodeExtraBytesToRead(extraBytes);
return encodingSpace;
}
public static void writeVInt(long value, DataOutput output) throws IOException
{
writeUnsignedVInt(encodeZigZag64(value), output);
}
/**
* Decode a ZigZag-encoded 64-bit value. ZigZag encodes signed integers
* into values that can be efficiently encoded with varint. (Otherwise,
* negative values must be sign-extended to 64 bits to be varint encoded,
* thus always taking 10 bytes on the wire.)
*
* @param n An unsigned 64-bit integer, stored in a signed int because
* Java has no explicit unsigned support.
* @return A signed 64-bit integer.
*/
public static long decodeZigZag64(final long n)
{
return (n >>> 1) ^ -(n & 1);
}
/**
* Encode a ZigZag-encoded 64-bit value. ZigZag encodes signed integers
* into values that can be efficiently encoded with varint. (Otherwise,
* negative values must be sign-extended to 64 bits to be varint encoded,
* thus always taking 10 bytes on the wire.)
*
* @param n A signed 64-bit integer.
* @return An unsigned 64-bit integer, stored in a signed int because
* Java has no explicit unsigned support.
*/
public static long encodeZigZag64(final long n)
{
// Note: the right-shift must be arithmetic
return (n << 1) ^ (n >> 63);
}
/** Compute the number of bytes that would be needed to encode a varint. */
public static int computeVIntSize(final long param)
{
return computeUnsignedVIntSize(encodeZigZag64(param));
}
/** Compute the number of bytes that would be needed to encode an unsigned varint. */
public static int computeUnsignedVIntSize(final long value)
{
int magnitude = Long.numberOfLeadingZeros(value | 1); // | with 1 to ensure magntiude <= 63, so (63 - 1) / 7 <= 8
return 9 - ((magnitude - 1) / 7);
}
}