/// <summary>
/// This method returns an uncompressed version of the given compressed byte array
/// </summary>
/// <param name="inputBlob">the byte array to be decompressed</param>
/// <param name="decompressedLength">the known length of the decompressed byte array</param>
/// <param name="compressionCode">a generation number that indicates what compression technique to use</param>
/// <returns>the decompressed byte array</returns>
public static unsafe Byte[] DecompressBlob(Byte[] inputBlob, int decompressedLength,
int compressionCode)
{
if (compressionCode == 1)
{
// the byte array of the output blob
Byte[] decompressedBlob = new Byte[decompressedLength];
// Decompress using LZFX algorithm.
// This method will throw an exception if the decompressed data does not
// exactly fit into the allocated array size.
LZFX.Decompress(inputBlob, decompressedBlob);
return(decompressedBlob);
}
if (compressionCode == 2)
{
// the byte array of the output blob
Byte[] decompressedBlob = new Byte[decompressedLength];
// Decompress using LZFX algorithm.
// This method will throw an exception if the decompressed data does not
// exactly fit into the allocated array size.
LZ4.Decompress(inputBlob, decompressedBlob);
return(decompressedBlob);
}
else
{ // return without doing any compression
return(inputBlob);
}
}
/// <summary>
/// This method computes the checksum for an individual trace of a time series, where the time
/// series is understood to be an ensemble of one or more traces. The checksum of a trace is
/// computed from the trace number and from the BLOB that contains the values for each time
/// step of the time series.
/// </summary>
/// <param name="traceNumber">the number for identifying the trace</param>
/// <param name="valueBlob">the BLOB that contains the values for each time step</param>
/// <returns>the Checksum as a byte[16] array</returns>
public static byte[] ComputeTraceChecksum(int traceNumber, byte[] valueBlob)
{
byte[] binArray = new byte[sizeof(Int32) + valueBlob.Length];
using (MemoryStream binStream = new MemoryStream(binArray))
using (BinaryWriter binWriter = new BinaryWriter(binStream))
{
binWriter.Write(traceNumber);
binWriter.Write(valueBlob);
// Use of BlockCopy follows the example at https://stackoverflow.com/a/5896716/2998072.
// 'longArray' pads the end with zeros and thereby create a 16-byte array in order
// to avoid upsetting code that was established when this checksum was based
// on 16-byte MurmurHash.
ulong[] longArray = new ulong[] { LZ4.GetXXHash64(binArray), 0 };
// Convert the longArray into a Byte array
Byte[] result = new Byte[16];
Buffer.BlockCopy(longArray, 0, result, 0, 16);
return(result);
}
}
/// <summary>
/// This returns a compressed version of the given byte array
/// </summary>
/// <param name="uncompressedBlob">the uncompressed byte array</param>
/// <param name="compressionCode">a generation number that indicates what compression technique to use</param>
/// <returns>the compressed byte array</returns>
public static unsafe Byte[] CompressBlob(Byte[] uncompressedBlob, int compressionCode)
{
if (compressionCode == 1)
{
Byte[] compressedBlob;
// the byte-array length of the input blob
int inputLength = uncompressedBlob.Length;
// The byte array that will be created by the compression.
// Note that some incompressible BLOBs will actually be made larger by LZFX
// compression. We have observed about 1% increase over the original BLOB,
// so the factor of 1.05 is expected to be safe. We add 16 since the factor
// of 1.05 is insufficient when the BLOB is very small.
compressedBlob = new Byte[(int)(inputLength * 1.05) + 16];
// Compress using LZFX algorithm.
// This method resizes the compressed byte array for us.
LZFX.Compress(uncompressedBlob, ref compressedBlob);
return(compressedBlob);
}
if (compressionCode == 2)
{
Byte[] compressedBlob;
// the byte-array length of the input blob
int inputLength = uncompressedBlob.Length;
// The byte array that will be created by the compression.
// Note that some incompressible BLOBs might actually be made larger by LZ4
// compression. The GetMaxSize method calls a function built into LZ4 which
// returns the maximum possible size of the output array. LZ4 documentation suggests
// that speed is optimized by allocating this max size.
compressedBlob = new Byte[(int)LZ4.GetMaxSize(inputLength)];
// Compress using LZ4 algorithm.
// This method resizes the compressed byte array for us.
LZ4.Compress(uncompressedBlob, ref compressedBlob, 4);
return(compressedBlob);
}
else
{ // return without doing any compression
return(uncompressedBlob);
}
}
