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need help to make crc calculation's class thread safe

when we added paralllism elaboration on our application (dotnet service) we found some unexpected behavoir on crc calculation over text documents.
to isolate the issue i created a test case. the crc calculation fails when invoked from parallel looop. in this test case replacing parallel foreach with standard always fine. I think i've to made so change in crc32 class implementation, but i need some help to understand the right way. Thanks.
this the test method.
[TestMethod()]
public void Test_Crc_TestoDoc()
{
string query = #"select top 100 docId from sometable";
///key is document's id
///value is a couple, crc and text
Dictionary<int, Tuple<int, string>> docs = new Dictionary<int, Tuple<int, string>>();
using (SqlDataReader oSqlDataReader = Utility.ExecuteSP_Reader(query))
{
while (oSqlDataReader.Read())
{
int docId = oSqlDataReader.GetInt32(0);
///retrive the text by docId
string docText = Utility.GetDocText(docId);
///calculate and add crc in dic
int CRC = CRC32.Compute(docText);
docs.Add(docId, new Tuple<int, string>(CRC, docText));
}
oSqlDataReader.Close();
}
///calculate crc 100 times to check if the value
///is always the same for same text
for (int i = 0; i < 100; i++)
{
Parallel.ForEach(docs.Keys,(int docId) =>
{
///crc saved in dictionary
int CRC1 = docs[docId].Item1;
///text saved in dictionary
string docText = docs[docId].Item2;
///calculate crc again, crc2 must be equal to crc1 stored in dictionary
int CRC2 = CRC32.Compute(docText);
Assert.AreEqual(CRC1, CRC2, $"crc not equal, why? docId->{docId} CRC1->{CRC1} CRC2->{CRC2}");
});
}
}
crc32 class:
public class CRC32 : HashAlgorithm
{
#region CONSTRUCTORS
/// <summary>Creates a CRC32 object using the <see cref="DefaultPolynomial"/>.</summary>
public CRC32()
: this(DefaultPolynomial)
{
}
/// <summary>Creates a CRC32 object using the specified polynomial.</summary>
/// <remarks>The polynomical should be supplied in its bit-reflected form. <see cref="DefaultPolynomial"/>.</remarks>
[CLSCompliant(false)]
public CRC32(uint polynomial)
{
HashSizeValue = 32;
_crc32Table = (uint[])_crc32TablesCache[polynomial];
if (_crc32Table == null)
{
_crc32Table = CRC32._buildCRC32Table(polynomial);
_crc32TablesCache.Add(polynomial, _crc32Table);
}
Initialize();
}
// static constructor
static CRC32()
{
_crc32TablesCache = Hashtable.Synchronized(new Hashtable());
_defaultCRC = new CRC32();
}
#endregion
#region PROPERTIES
/// <summary>Gets the default polynomial (used in WinZip, Ethernet, etc.)</summary>
/// <remarks>The default polynomial is a bit-reflected version of the standard polynomial 0x04C11DB7 used by WinZip, Ethernet, etc.</remarks>
[CLSCompliant(false)]
public static readonly uint DefaultPolynomial = 0xEDB88320; // Bitwise reflection of 0x04C11DB7;
#endregion
#region METHODS
/// <summary>Initializes an implementation of HashAlgorithm.</summary>
public override void Initialize()
{
_crc = _allOnes;
}
/// <summary>Routes data written to the object into the hash algorithm for computing the hash.</summary>
protected override void HashCore(byte[] buffer, int offset, int count)
{
for (int i = offset; i < count; i++)
{
ulong ptr = (_crc & 0xFF) ^ buffer[i];
_crc >>= 8;
_crc ^= _crc32Table[ptr];
}
}
/// <summary>Finalizes the hash computation after the last data is processed by the cryptographic stream object.</summary>
protected override byte[] HashFinal()
{
byte[] finalHash = new byte[4];
ulong finalCRC = _crc ^ _allOnes;
finalHash[0] = (byte)((finalCRC >> 0) & 0xFF);
finalHash[1] = (byte)((finalCRC >> 8) & 0xFF);
finalHash[2] = (byte)((finalCRC >> 16) & 0xFF);
finalHash[3] = (byte)((finalCRC >> 24) & 0xFF);
return finalHash;
}
/// <summary>Computes the CRC32 value for the given ASCII string using the <see cref="DefaultPolynomial"/>.</summary>
public static int Compute(string asciiString)
{
_defaultCRC.Initialize();
return ToInt32(_defaultCRC.ComputeHash(asciiString));
}
/// <summary>Computes the CRC32 value for the given input stream using the <see cref="DefaultPolynomial"/>.</summary>
public static int Compute(Stream inputStream)
{
_defaultCRC.Initialize();
return ToInt32(_defaultCRC.ComputeHash(inputStream));
}
/// <summary>Computes the CRC32 value for the input data using the <see cref="DefaultPolynomial"/>.</summary>
public static int Compute(byte[] buffer)
{
_defaultCRC.Initialize();
return ToInt32(_defaultCRC.ComputeHash(buffer));
}
/// <summary>Computes the hash value for the input data using the <see cref="DefaultPolynomial"/>.</summary>
public static int Compute(byte[] buffer, int offset, int count)
{
_defaultCRC.Initialize();
return ToInt32(_defaultCRC.ComputeHash(buffer, offset, count));
}
/// <summary>Computes the hash value for the given ASCII string.</summary>
/// <remarks>The computation preserves the internal state between the calls, so it can be used for computation of a stream data.</remarks>
public byte[] ComputeHash(string asciiString)
{
byte[] rawBytes = ASCIIEncoding.ASCII.GetBytes(asciiString);
return ComputeHash(rawBytes);
}
/// <summary>Computes the hash value for the given input stream.</summary>
/// <remarks>The computation preserves the internal state between the calls, so it can be used for computation of a stream data.</remarks>
new public byte[] ComputeHash(Stream inputStream)
{
byte[] buffer = new byte[4096];
int bytesRead;
while ((bytesRead = inputStream.Read(buffer, 0, 4096)) > 0)
{
HashCore(buffer, 0, bytesRead);
}
return HashFinal();
}
/// <summary>Computes the hash value for the input data.</summary>
/// <remarks>The computation preserves the internal state between the calls, so it can be used for computation of a stream data.</remarks>
new public byte[] ComputeHash(byte[] buffer)
{
return ComputeHash(buffer, 0, buffer.Length);
}
/// <summary>Computes the hash value for the input data.</summary>
/// <remarks>The computation preserves the internal state between the calls, so it can be used for computation of a stream data.</remarks>
new public byte[] ComputeHash(byte[] buffer, int offset, int count)
{
HashCore(buffer, offset, count);
return HashFinal();
}
#endregion
#region PRIVATE SECTION
private static uint _allOnes = 0xffffffff;
private static CRC32 _defaultCRC;
private static Hashtable _crc32TablesCache;
private uint[] _crc32Table;
private uint _crc;
// Builds a crc32 table given a polynomial
private static uint[] _buildCRC32Table(uint polynomial)
{
uint crc;
uint[] table = new uint[256];
// 256 values representing ASCII character codes.
for (int i = 0; i < 256; i++)
{
crc = (uint)i;
for (int j = 8; j > 0; j--)
{
if ((crc & 1) == 1)
crc = (crc >> 1) ^ polynomial;
else
crc >>= 1;
}
table[i] = crc;
}
return table;
}
private static int ToInt32(byte[] buffer)
{
return BitConverter.ToInt32(buffer, 0);
}
#endregion
}

Probably the problem are all the "static" function.
In fact, a static function is the same for all of the instance of CRC32.
That means that while an instance is running, setting his parameter, another can write his own value over the first one.

How to Call to HashPassword and to store User password to database?

I'm setting up a HashPassword function using SHA1CryptoServiceProvider(). My requirement includes two methods: generate the salt and initializer which I need help with.
Salt is used with the IV which is used to salt the password before it is hashed, and the password to validate. The initializer takes the string made by the salt generator it mixes the password and salt into one string and add's any extra characters to the end then hash the blended password and returns the value.
Essentially, I need to compare if the value sent from the view differs from the original and if it does then i need to regenerate the hash and initializer on a create(new record).
This controller action calls the HashPassword functions in the USERController.Helper file.
public ActionResult HashPassword(USERSModel UsersModel)
{
USERDto dto = new USERDto();
if (ModelState.IsValid)
{
string hashedPassword = UsersModel.PASSWORD;
UsersModel.PASSWORD = hashedPassword;
dto.Updated.Add(hashedPassword);
dto.Updated.Add("NAME");
dto.Updated.Add("ID");
dto.Updated.Add("PASSWORD");
UsersModel.Updated.SaveChanges();
ViewBag.Message = "User was added successfully!";
UsersModel = new USERSModel();
}
else
ViewBag.message = "Error in adding User!";
return View("USERSSettingsPartial", UsersModel);
}
/// <summary>
/// Called to hash a user password to be stored in the DB.
/// </summary>
/// <param name="password">The password to validate.</param>
/// <param name="salt">The IV used to salt the password before it is hashed.</param>
/// <param name="errorDesc">Returns an error description if an error occurs.</param>
/// <returns>Returns the hashed password as a HEX string on success, otherwise returns null.</returns>
private string HashPassword(string password, byte[] salt, ref string errorDesc)
{
try
{
byte[] newPassword = Encoding.ASCII.GetBytes(password.ToUpper());
if (salt != null && salt.Length > 0)
{
int count = (salt.Length < newPassword.Length) ? salt.Length : newPassword.Length;
byte[] temp = new byte[salt.Length + newPassword.Length];
for (int index = 0; index < count; index++)
{
temp[index * 2] = newPassword[index];
temp[index * 2 + 1] = salt[index];
}
if (count == salt.Length && count < newPassword.Length)
Buffer.BlockCopy(newPassword, count, temp, count * 2, newPassword.Length - count);
else if (count == newPassword.Length && count < salt.Length)
Buffer.BlockCopy(salt, count, temp, count * 2, salt.Length - count);
newPassword = temp;
}
using (var hash = new System.Security.Cryptography.SHA1CryptoServiceProvider())
{
hash.ComputeHash(newPassword);
return this.GetHexStringFromBytes(hash.Hash);
}
}
catch (Exception Ex)
{
errorDesc = Ex.Message;
if (Ex.InnerException != null) errorDesc = string.Format("{0}\r\n{1}", errorDesc, Ex.InnerException.Message);
}
return null;
}
/// <summary>
/// called to convert byte data into hexidecimal string were each byte is represented as two hexidecimal characters.
/// </summary>
/// <param name="data">Byte data to convert.</param>
/// <returns>A hexidecimal string version of the data.</returns>
private string GetHexStringFromBytes(byte[] data)
{
if (data == null || data.Length == 0) return string.Empty;
StringBuilder sbHex = new StringBuilder();
for (int index = 0; index < data.Length; index++) sbHex.AppendFormat(null, "{0:X2}", data[index]);
return sbHex.ToString();
}
/// <summary>
/// called to convert hexadecimal string into byte data were two hexadecimal characters are converted into a byte.
/// </summary>
/// <param name="hexString">A hexidecimal string to convert</param>
/// <returns>The converted byte data.</returns>
private byte[] GetBytesFromHexString(string hexString)
{
if (string.IsNullOrEmpty(hexString)) return null;
byte[] data = new byte[hexString.Length / 2];
for (int index = 0; index < data.Length; index++)
{
data[index] = byte.Parse(hexString.Substring(index * 2, 2), System.Globalization.NumberStyles.AllowHexSpecifier);
}
return data;
}
This is my first go around with a project like this, therefore I don't have any output. Just need examples to understand better.

Basically needed to have a Controller in a Service where this class will create the salt and be called from a Controller Helper class. What I did was set the Initializer on the server side where in turn added code to the USERS service controller create IHttpActionResult which sets the salt and password. You never want to store passwords in your database, always want to hash them.
I created a request in the service controller of the USERS passing in DTO which is used to create a new record, returning an object containing the query results if any, otherwise returns not found or internal server error message. Within this method Salt is being called:
public IHttpActionResult Create([FromBody]USERDto dto)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
try
{
byte[] saltValue;
string error = string.Empty;
saltValue = GenerateSalt();
dto.INITIALIZER = GetHexStringFromBytes(saltValue);
dto.PASSWORD = HashPassword(dto.PASSWORD, saltValue, ref error);
USERDto created = USERSProcessor.Create(dto);
if (created == null)
{
return NotFound();
}
return Ok(created);
}
catch (Exception ex)
{
LogUtility.LogError(ex);
return InternalServerError(ex);
}
}
Then (to not clutter controller) I created a controller helper class & added this code to implement the hashing salt methods, where the USERSController calls to the hash password to be stored in the database, as well as the dto.INITIALIZER is called to convert byte data into hexadecimal string where each byte is represented as two hexadecimal characters:
partial class USERSController
{
/// <summary>
/// Called to generate salt byte array.
/// </summary>
/// <returns>The generated salt byte array.</returns>
public static byte[] GenerateSalt()
{
byte[] iv;
using (var alg = new AesCryptoServiceProvider())
{
alg.BlockSize = 128; //block size is 8bytes, which is the the size of the IV generated.
alg.KeySize = 256; //key size is 32bytes
alg.GenerateIV();
iv = alg.IV;
}
return iv;
}
/// <summary>
/// Called to hash a user password to be stored in DB.
/// </summary>
/// <param name="password">The password to validate.</param>
/// <param name="salt">The IV used to salt the password before it is hashed.</param>
/// <param name="errorDesc">Returns an error description if an error occurs.</param>
/// <returns>Returns the hashed password as a HEX string on success, otherwise returns null.</returns>
private static string HashPassword(string password, byte[] salt, ref string errorDesc)
{
try
{
byte[] newPassword = Encoding.ASCII.GetBytes(password.ToUpper());
if (salt != null && salt.Length > 0)
{
int count = (salt.Length < newPassword.Length) ? salt.Length : newPassword.Length;
byte[] temp = new byte[salt.Length + newPassword.Length];
for (int index = 0; index < count; index++)
{
temp[index * 2] = newPassword[index];
temp[index * 2 + 1] = salt[index];
}
if (count == salt.Length && count < newPassword.Length)
Buffer.BlockCopy(newPassword, count, temp, count * 2, newPassword.Length - count);
else if (count == newPassword.Length && count < salt.Length)
Buffer.BlockCopy(salt, count, temp, count * 2, salt.Length - count);
newPassword = temp;
}
using (var hash = new System.Security.Cryptography.SHA1CryptoServiceProvider())
{
hash.ComputeHash(newPassword);
return GetHexStringFromBytes(hash.Hash);
}
}
catch (Exception Ex)
{
errorDesc = Ex.Message;
if (Ex.InnerException != null) errorDesc = string.Format("{0}\r\n{1}", errorDesc, Ex.InnerException.Message);
}
return null;
}
/// <summary>
/// called to convert byte data into hexidecimal string were each byte is represented as two hexidecimal characters.
/// </summary>
/// <param name="data">Byte data to convert.</param>
/// <returns>A hexidecimal string version of the data.</returns>
private static string GetHexStringFromBytes(byte[] data)
{
if (data == null || data.Length == 0) return string.Empty;
StringBuilder sbHex = new StringBuilder();
for (int index = 0; index < data.Length; index++) sbHex.AppendFormat(null, "{0:X2}", data[index]);
return sbHex.ToString();
}
/// <summary>
/// called to convert hexidecimal string into byte data were two hexidecimal characters are converted into a byte.
/// </summary>
/// <param name="hexString">A hexidecimal string to convert</param>
/// <returns>The converted byte data.</returns>
private static byte[] GetBytesFromHexString(string hexString)
{
if (string.IsNullOrEmpty(hexString)) return null;
byte[] data = new byte[hexString.Length / 2];
for (int index = 0; index < data.Length; index++)
{
data[index] = byte.Parse(hexString.Substring(index * 2, 2), System.Globalization.NumberStyles.AllowHexSpecifier);
}
return data;
}
}

Porting a Decoder Script to Objective C

I’m working on an Objective C app which receives GPS routes from a server. The routes are encoded and I have the decoding scripts written in both PHP and C#.
To my knowledge there it's not possible to compile or import the script into the Xcode project.
I have attached the two scripts below alongside a copy of the encoded GPS route.
I've studied the script a considerable amount and understand (for the most part) what is happening.) Is it feasible to port this code to Objective C? If so what would be the best approach? And how would I port the byte streams?
I'm slightly confused since I have never worked with encoding/decoding before, but any help is highly appreciated.
Encoded GPS Route
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
C# Decode Script
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
// Classes for managing IOF XML 3.0 Route element.
// IOF XML 3.0 specification: http://code.google.com/p/iofdatastandard/source/browse/trunk/IOF.xsd.
// IOF XML 3.0 example result list file with Route element: http://code.google.com/p/iofdatastandard/source/browse/trunk/Examples/ResultList1.xml.
/// <summary>
/// Class representing a route, including logic for converting to/from an IOF XML 3.0 route stored in binary format.
/// </summary>
public class IofXml30Route
{
private double? length;
private IEnumerable<IofXml30Waypoint> waypoints = new List<IofXml30Waypoint>();
/// <summary>
/// The waypoints of the route.
/// </summary>
public IEnumerable<IofXml30Waypoint> Waypoints
{
get { return waypoints; }
set { waypoints = value ?? new List<IofXml30Waypoint>(); }
}
/// <summary>
/// Writes the route in IOF XML 3.0 binary format to the specified stream.
/// </summary>
/// <param name="stream">The stream to write to.</param>
public void WriteToStream(Stream stream)
{
IofXml30Waypoint previousWaypoint = null;
foreach (var waypoint in Waypoints)
{
waypoint.WriteToStream(stream, previousWaypoint);
previousWaypoint = waypoint;
}
}
/// <summary>
/// Converts the route to IOF XML 3.0 binary format and returns it as a base64-encoded string.
/// </summary>
/// <param name="formattingOptions">The formatting options for the base64-encoded string.</param>
public string ToBase64String(Base64FormattingOptions formattingOptions = Base64FormattingOptions.None)
{
return Convert.ToBase64String(ToByteArray(), formattingOptions);
}
/// <summary>
/// Converts the route to IOF XML 3.0 binary format and returns it as a byte array.
/// </summary>
public byte[] ToByteArray()
{
using (var ms = new MemoryStream())
{
WriteToStream(ms);
return ms.ToArray();
}
}
/// <summary>
/// Reads a route in IOF XML 3.0 binary format from a stream.
/// </summary>
/// <param name="stream">The stream to read from.</param>
public static IofXml30Route FromStream(Stream stream)
{
var waypoints = new List<IofXml30Waypoint>();
while (stream.Position < stream.Length)
{
waypoints.Add(IofXml30Waypoint.FromStream(stream, waypoints.LastOrDefault()));
}
return new IofXml30Route() { Waypoints = waypoints };
}
/// <summary>
/// Reads a route in IOF XML 3.0 binary format from a base64-encoded string.
/// </summary>
/// <param name="base64String">The base64-encoded string to read from.</param>
public static IofXml30Route FromBase64String(string base64String)
{
return FromByteArray(Convert.FromBase64String(base64String));
}
/// <summary>
/// Reads a route in IOF XML 3.0 binary format from a byte array.
/// </summary>
/// <param name="bytes">The bytes to read from.</param>
public static IofXml30Route FromByteArray(byte[] bytes)
{
using (var ms = new MemoryStream(bytes))
{
return FromStream(ms);
}
}
/// <summary>
/// Gets the length of the route in meters.
/// </summary>
public double Length
{
get { return length ?? (length = CalculateLength()).Value; }
}
/// <summary>
/// Gets the start time of the route.
/// </summary>
public DateTime StartTime
{
get { return Waypoints.Any() ? Waypoints.First().Time : DateTime.MinValue; }
}
/// <summary>
/// Gets the end time of the route.
/// </summary>
public DateTime EndTime
{
get { return Waypoints.Any() ? Waypoints.Last().Time : DateTime.MinValue; }
}
/// <summary>
/// Gets the duration of the route.
/// </summary>
public TimeSpan Duration
{
get { return EndTime - StartTime; }
}
private double CalculateLength()
{
var sum = 0.0;
var wpList = Waypoints.ToList();
for(var i=1; i<Waypoints.Count(); i++)
{
sum += GetDistanceBetweenWaypoints(wpList[i - 1], wpList[i]);
}
return sum;
}
private static double GetDistanceBetweenWaypoints(IofXml30Waypoint w1, IofXml30Waypoint w2)
{
// use spherical coordinates: rho, phi, theta
const double rho = 6378200; // earth radius in metres
double sinPhi0 = Math.Sin(0.5 * Math.PI + w1.Latitude / 180.0 * Math.PI);
double cosPhi0 = Math.Cos(0.5 * Math.PI + w1.Latitude / 180.0 * Math.PI);
double sinTheta0 = Math.Sin(w1.Longitude / 180.0 * Math.PI);
double cosTheta0 = Math.Cos(w1.Longitude / 180.0 * Math.PI);
double sinPhi1 = Math.Sin(0.5 * Math.PI + w2.Latitude / 180.0 * Math.PI);
double cosPhi1 = Math.Cos(0.5 * Math.PI + w2.Latitude / 180.0 * Math.PI);
double sinTheta1 = Math.Sin(w2.Longitude / 180.0 * Math.PI);
double cosTheta1 = Math.Cos(w2.Longitude / 180.0 * Math.PI);
var x1 = rho * sinPhi0 * cosTheta0;
var y1 = rho * sinPhi0 * sinTheta0;
var z1 = rho * cosPhi0;
var x2 = rho * sinPhi1 * cosTheta1;
var y2 = rho * sinPhi1 * sinTheta1;
var z2 = rho * cosPhi1;
return DistancePointToPoint(x1, y1, z1, x2, y2, z2);
}
private static double DistancePointToPoint(double x1, double y1, double z1, double x2, double y2, double z2)
{
var sum = (x2 - x1)*(x2 - x1) + (y2 - y1)*(y2 - y1) + (z2 - z1)*(z2 - z1);
return Math.Sqrt(sum);
}
}
/// <summary>
/// Class representing a waypoint, including logic for converting to/from an IOF XML 3.0 waypoint stored in binary format.
/// </summary>
public class IofXml30Waypoint
{
private static readonly DateTime zeroTime = new DateTime(1900, 01, 01, 00, 00, 00, DateTimeKind.Utc);
private const long timeSecondsThreshold = 255;
private const long timeMillisecondsThreshold = 65535;
private const int lanLngBigDeltaLowerThreshold = -32768;
private const int lanLngBigDeltaUpperThreshold = 32767;
private const int lanLngSmallDeltaLowerThreshold = -128;
private const int lanLngSmallDeltaUpperThreshold = 127;
private const int altitudeDeltaLowerThreshold = -128;
private const int altitudeDeltaUpperThreshold = 127;
/// <summary>
/// Gets or sets the type of the waypoint; normal or interruption.
/// </summary>
public IofXml30WaypointType Type { get; set; }
/// <summary>
/// Gets or sets the time when the waypoint was recorded.
/// </summary>
public DateTime Time { get; set; }
/// <summary>
/// Gets or sets the latitude of the waypoint.
/// </summary>
public double Latitude { get; set; }
/// <summary>
/// Gets or sets the longitude of the waypoint.
/// </summary>
public double Longitude { get; set; }
/// <summary>
/// Gets or sets the altitude of the waypoint.
/// </summary>
public double? Altitude { get; set; }
/// <summary>
/// Gets or sets the the time when the waypoint was recorded in the internal storage mode.
/// </summary>
public ulong StorageTime
{
get { return (ulong)Math.Round((Time - zeroTime).TotalMilliseconds); }
set { Time = zeroTime.AddMilliseconds(value); }
}
/// <summary>
/// Gets or sets the latitude of the waypoint in the internal storage mode.
/// </summary>
public int StorageLatitude
{
get { return (int)Math.Round(Latitude * 1000000); }
set { Latitude = (double)value / 1000000; }
}
/// <summary>
/// Gets or sets the longitude of the waypoint in the internal storage mode.
/// </summary>
public int StorageLongitude
{
get { return (int)Math.Round(Longitude * 1000000); }
set { Longitude = (double)value / 1000000; }
}
/// <summary>
/// Gets or sets the altitude of the waypoint in the internal storage mode.
/// </summary>
public int? StorageAltitude
{
get { return Altitude == null ? (int?)null : (int)Math.Round(Altitude.Value * 10); }
set { Altitude = value == null ? (double?)null : (double)value / 10; }
}
/// <summary>
/// Writes the waypoint in IOF XML 3.0 binary format to a stream.
/// </summary>
/// <param name="stream">The stream to write to.</param>
/// <param name="previousWaypoint">The previous waypoint of the route, or null if this is the first waypoint.</param>
public void WriteToStream(Stream stream, IofXml30Waypoint previousWaypoint)
{
var timeStorageMode = TimeStorageMode.Full;
if (previousWaypoint != null)
{
if ((StorageTime - previousWaypoint.StorageTime) % 1000 == 0 && (StorageTime - previousWaypoint.StorageTime) / 1000 <= timeSecondsThreshold)
{
timeStorageMode = TimeStorageMode.Seconds;
}
else if (StorageTime - previousWaypoint.StorageTime <= timeMillisecondsThreshold)
{
timeStorageMode = TimeStorageMode.Milliseconds;
}
}
var positionStorageMode = PositionStorageMode.Full;
if (previousWaypoint != null &&
(StorageAltitude == null || (previousWaypoint.StorageAltitude != null && StorageAltitude - previousWaypoint.StorageAltitude >= altitudeDeltaLowerThreshold && StorageAltitude - previousWaypoint.StorageAltitude <= altitudeDeltaUpperThreshold)))
{
if (StorageLatitude - previousWaypoint.StorageLatitude >= lanLngSmallDeltaLowerThreshold && StorageLatitude - previousWaypoint.StorageLatitude <= lanLngSmallDeltaUpperThreshold &&
StorageLongitude - previousWaypoint.StorageLongitude >= lanLngSmallDeltaLowerThreshold && StorageLongitude - previousWaypoint.StorageLongitude <= lanLngSmallDeltaUpperThreshold)
{
positionStorageMode = PositionStorageMode.SmallDelta;
}
else if (StorageLatitude - previousWaypoint.StorageLatitude >= lanLngBigDeltaLowerThreshold && StorageLatitude - previousWaypoint.StorageLatitude <= lanLngBigDeltaUpperThreshold &&
StorageLongitude - previousWaypoint.StorageLongitude >= lanLngBigDeltaLowerThreshold && StorageLongitude - previousWaypoint.StorageLongitude <= lanLngBigDeltaUpperThreshold)
{
positionStorageMode = PositionStorageMode.BigDelta;
}
}
var headerByte = 0;
if (Type == IofXml30WaypointType.Interruption) headerByte |= (1 << 7);
if (timeStorageMode == TimeStorageMode.Milliseconds) headerByte |= (1 << 6);
if (timeStorageMode == TimeStorageMode.Seconds) headerByte |= (1 << 5);
if (positionStorageMode == PositionStorageMode.BigDelta) headerByte |= (1 << 4);
if (positionStorageMode == PositionStorageMode.SmallDelta) headerByte |= (1 << 3);
if (StorageAltitude != null) headerByte |= (1 << 2);
// header byte
stream.WriteByte((byte)headerByte);
// time byte(s)
switch (timeStorageMode)
{
case TimeStorageMode.Full: // 6 bytes
stream.Write(BitConverter.GetBytes(StorageTime).Reverse().ToArray(), 2, 6);
break;
case TimeStorageMode.Milliseconds: // 2 bytes
stream.Write(BitConverter.GetBytes((ushort)(StorageTime - previousWaypoint.StorageTime)).Reverse().ToArray(), 0, 2);
break;
case TimeStorageMode.Seconds: // 1 byte
stream.WriteByte((byte)((StorageTime - previousWaypoint.StorageTime) / 1000));
break;
}
// position bytes
switch (positionStorageMode)
{
case PositionStorageMode.Full: // 4 + 4 + 3 bytes
stream.Write(BitConverter.GetBytes(StorageLatitude).Reverse().ToArray(), 0, 4);
stream.Write(BitConverter.GetBytes(StorageLongitude).Reverse().ToArray(), 0, 4);
if (StorageAltitude != null) stream.Write(BitConverter.GetBytes(StorageAltitude.Value).Reverse().ToArray(), 1, 3);
break;
case PositionStorageMode.BigDelta: // 2 + 2 + 1 bytes
stream.Write(BitConverter.GetBytes((short)(StorageLatitude - previousWaypoint.StorageLatitude)).Reverse().ToArray(), 0, 2);
stream.Write(BitConverter.GetBytes((short)(StorageLongitude - previousWaypoint.StorageLongitude)).Reverse().ToArray(), 0, 2);
if (StorageAltitude != null) stream.Write(BitConverter.GetBytes((sbyte)(StorageAltitude - previousWaypoint.StorageAltitude).Value), 0, 1);
break;
case PositionStorageMode.SmallDelta: // 1 + 1 + 1 bytes
stream.Write(BitConverter.GetBytes((sbyte)(StorageLatitude - previousWaypoint.StorageLatitude)), 0, 1);
stream.Write(BitConverter.GetBytes((sbyte)(StorageLongitude - previousWaypoint.StorageLongitude)), 0, 1);
if (StorageAltitude != null) stream.Write(BitConverter.GetBytes((sbyte)(StorageAltitude - previousWaypoint.StorageAltitude).Value), 0, 1);
break;
}
}
/// <summary>
/// Reads a waypoint in IOF XML 3.0 binary format from a stream.
/// </summary>
/// <param name="stream">The stream to read from.</param>
/// <param name="previousWaypoint">The previous waypoint of the route, or null if this is the first waypoint.</param>
/// <returns></returns>
public static IofXml30Waypoint FromStream(Stream stream, IofXml30Waypoint previousWaypoint)
{
var waypoint = new IofXml30Waypoint();
// header byte
var headerByte = stream.ReadByte();
waypoint.Type = (headerByte & (1 << 7)) == 0 ? IofXml30WaypointType.Normal : IofXml30WaypointType.Interruption;
var timeStorageMode = TimeStorageMode.Full;
if ((headerByte & (1 << 6)) > 0)
{
timeStorageMode = TimeStorageMode.Milliseconds;
}
else if ((headerByte & (1 << 5)) > 0)
{
timeStorageMode = TimeStorageMode.Seconds;
}
var positionStorageMode = PositionStorageMode.Full;
if ((headerByte & (1 << 4)) > 0)
{
positionStorageMode = PositionStorageMode.BigDelta;
}
else if ((headerByte & (1 << 3)) > 0)
{
positionStorageMode = PositionStorageMode.SmallDelta;
}
var altitudePresent = (headerByte & (1 << 2)) > 0;
byte[] bytes;
int b;
// time byte(s)
switch (timeStorageMode)
{
case TimeStorageMode.Full: // 4 bytes
bytes = new byte[8];
stream.Read(bytes, 2, 6);
waypoint.StorageTime = BitConverter.ToUInt64(bytes.Reverse().ToArray(), 0);
break;
case TimeStorageMode.Milliseconds: // 2 bytes
bytes = new byte[2];
stream.Read(bytes, 0, 2);
waypoint.StorageTime = previousWaypoint.StorageTime + BitConverter.ToUInt16(bytes.Reverse().ToArray(), 0);
break;
case TimeStorageMode.Seconds: // 1 byte
b = stream.ReadByte();
waypoint.StorageTime = previousWaypoint.StorageTime + (ulong)b * 1000;
break;
}
// position bytes
switch (positionStorageMode)
{
case PositionStorageMode.Full: // 4 + 4 + 3 bytes
bytes = new byte[4];
stream.Read(bytes, 0, 4);
waypoint.StorageLatitude = BitConverter.ToInt32(bytes.Reverse().ToArray(), 0);
bytes = new byte[4];
stream.Read(bytes, 0, 4);
waypoint.StorageLongitude = BitConverter.ToInt32(bytes.Reverse().ToArray(), 0);
if (altitudePresent)
{
bytes = new byte[4];
stream.Read(bytes, 1, 3);
waypoint.StorageAltitude = BitConverter.ToInt32(bytes.Reverse().ToArray(), 0);
}
break;
case PositionStorageMode.BigDelta: // 2 + 2 + 1 bytes
bytes = new byte[2];
stream.Read(bytes, 0, 2);
waypoint.StorageLatitude = previousWaypoint.StorageLatitude + BitConverter.ToInt16(bytes.Reverse().ToArray(), 0);
bytes = new byte[2];
stream.Read(bytes, 0, 2);
waypoint.StorageLongitude = previousWaypoint.StorageLongitude + BitConverter.ToInt16(bytes.Reverse().ToArray(), 0);
if (altitudePresent)
{
b = stream.ReadByte();
waypoint.StorageAltitude = previousWaypoint.StorageAltitude + (sbyte)b;
}
break;
case PositionStorageMode.SmallDelta: // 1 + 1 + 1 bytes
b = stream.ReadByte();
waypoint.StorageLatitude = previousWaypoint.StorageLatitude + (sbyte)b;
b = stream.ReadByte();
waypoint.StorageLongitude = previousWaypoint.StorageLongitude + (sbyte)b;
if (altitudePresent)
{
b = stream.ReadByte();
waypoint.StorageAltitude = previousWaypoint.StorageAltitude + (sbyte)b;
}
break;
}
return waypoint;
}
/// <summary>
/// The storage mode for the time of a waypoint.
/// </summary>
private enum TimeStorageMode
{
/// <summary>
/// The time is stored as a 6-byte unsigned integer, and shows the number of milliseconds since January 1, 1900, 00:00:00 UTC.
/// </summary>
Full,
/// <summary>
/// The time is stored as a 2-byte unsigned integer, and shows the number of seconds since the previous waypoint's time.
/// </summary>
Seconds,
/// <summary>
/// The time is stored as a 4-byte unsigned integer, and shows the number of milliseconds since the previous waypoint's time.
/// </summary>
Milliseconds
}
/// <summary>
/// The storage mode for the position (latitude, longitude, altitude) of a waypoint.
/// </summary>
private enum PositionStorageMode
{
/// <summary>
/// The longitude and latitude are stored as microdegrees in 4-byte signed integers, and the altitude is stored as decimeters in a 3-byte signed integer.
/// </summary>
Full,
/// <summary>
/// The longitude and latitude are stored as microdegrees relative to the previous waypoint in 2-byte signed integers, and the altitude is stored as decimeters relative to the previous waypoint in a 3-byte signed integer>.
/// </summary>
BigDelta,
/// <summary>
/// The longitude and latitude are stored as microdegrees relative to the previous waypoint in 1-byte signed integers, and the altitude is stored as decimeters relative to the previous waypoint in a 1-byte signed integer.
/// </summary>
SmallDelta
}
}
/// <summary>
/// The type of waypoint.
/// </summary>
public enum IofXml30WaypointType
{
/// <summary>
/// A normal waypoint.
/// </summary>
Normal,
/// <summary>
/// A waypoint that is the last waypoint before an interruption in the route occurs.
/// </summary>
Interruption
}
PHP Decode Script
The PHP script is very similar. I can't attach due to the limit of the size of this post, however I can provide it if needed.

How to call a C# class's static method from VB.Net?

I have a C# dll and want to use it in VB.NET. I'm using C# 2008 Express and VB 2008 Express. I have added a reference in a VB project to the C# dll. When I create an instane of a class in the C# dll, it gives the following error messsage: "Type 'RF.RabinFingerprint' has no constructors". How do I fix this?
My C# dll code:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace RF
{
/// <summary>
/// Génère des empreintes de fichiers
/// </summary>
public static class RabinFingerprint
{
/// <summary>
/// Bit 64 of the polynomial P is always 1 and not treated directly. This is the polynomial
/// with the leading coefficient removed (lcr).
/// Represents t^64 + t^4 + t^3 + t + 1.
/// </summary>
private static readonly UInt64 p_lcr = 0x000000000000001BL;
/// <summary>
/// It's not necessary to provide definitions for such integral constant variables as long as their
/// addresses are not taken.
/// Degree of the polynomial P.
/// </summary>
private static readonly int K = 64;
/// <summary>
/// Represents t^(K-1)
/// </summary>
private static readonly UInt64 T_K_minus_1 = (UInt64)1L << (K - 1);
/// <summary>
/// Broder's paper presents four pre-computed tables because words are considered to be 32-bit.
/// In this implementation W is a 64-bit integral type. Eight tables are used.
/// Table A is i1^127 + i2^126 + ... + i8^120.
/// Table B is i1^119 + i2^118 + ... + i8^112.
/// Table C, D, ..
/// Table E is i1^95 + i2^94 + ... + i8^88. (This is table A in the paper.)
/// Table F, G, H.
/// </summary>
private static UInt64[] tableA_ = new UInt64[256]; //Assuming byte size 8.
private static UInt64[] tableB_ = new UInt64[256];
private static UInt64[] tableC_ = new UInt64[256];
private static UInt64[] tableD_ = new UInt64[256];
private static UInt64[] tableE_ = new UInt64[256];
private static UInt64[] tableF_ = new UInt64[256];
private static UInt64[] tableG_ = new UInt64[256];
private static UInt64[] tableH_ = new UInt64[256];
/// <summary>
/// Constructor
/// </summary>
static RabinFingerprint()
{
InitTables();
}
/// <summary>
/// Initialize tables
/// </summary>
private static void InitTables()
{
//This represents t^(k + i) mod P, where i is the index of the array.
//It will be used to compute the tables.
UInt64[] mods = new UInt64[K];
//Remember t^k mod P is equivalent to p_lcr.
mods[0] = p_lcr;
for (int i = 1; i < K; ++i)
{
//By property: t^i mod P = t(t^(i - 1)) mod P.
mods[i] = mods[i - 1] << 1;
//If mods[i - 1] had a term at k-1, mods[i] would have had the term k, which is not represented.
//The term k would account for exactly one more division by P. Then, the effect is the same
//as adding p_lcr to the mod.
if ((mods[i - 1] & T_K_minus_1) != 0)
mods[i] ^= p_lcr;
}
//Compute tables. A control variable is used to indicate whether the current bit should be
//considered.
for (int i = 0; i < 256; ++i)
{
int control = i;
for (int j = 0; j < 8 && control > 0; ++j)
{
// bool.Parse(Convert.ToString())
if ((control & 1) == 1) //Ok, consider bit. ((byte))
{
tableA_[i] ^= mods[j + 56];
tableB_[i] ^= mods[j + 48];
tableC_[i] ^= mods[j + 40];
tableD_[i] ^= mods[j + 32];
tableE_[i] ^= mods[j + 24];
tableF_[i] ^= mods[j + 16];
tableG_[i] ^= mods[j + 8];
tableH_[i] ^= mods[j];
}
control >>= 1;
}
}
}
/// <summary>
/// Compute hash key
/// </summary>
/// <param name="value">Value to hash</param>
/// <returns>Value</returns>
private static UInt64 ComputeTablesSum(ref UInt64 value)
{
value = tableH_[((value) & 0xFF)] ^
tableG_[((value >> 8) & 0xFF)] ^
tableF_[((value >> 16) & 0xFF)] ^
tableE_[((value >> 24) & 0xFF)] ^
tableD_[((value >> 32) & 0xFF)] ^
tableC_[((value >> 40) & 0xFF)] ^
tableB_[((value >> 48) & 0xFF)] ^
tableA_[((value >> 56) & 0xFF)];
return value; //Pass by reference to return the same w. (Convenience and efficiency.)
}
/// <summary>
/// Compute hask hey
/// </summary>
/// <param name="HashArray">Array of Ulong bytes to ahsh</param>
/// <returns>Hash key</returns>
private static UInt64 Compute(UInt64[] HashArray)
{
UInt64 w = 0L;
for (int s = 0; s < HashArray.Length; ++s)
w = ComputeTablesSum(ref w) ^ HashArray[s];
return w;
}
/// <summary>
/// Compute the fingerprint
/// </summary>
/// <param name="source">String to compute</param>
/// <returns>Hash key</returns>
public static UInt64 ComputeFingerPrint(string source)
{
byte[] table = Encoding.Unicode.GetBytes(source);
UInt64[] values = new UInt64[table.LongLength];
ConvertBytes(ref table, ref values);
return Compute(values);
}
/// <summary>
/// Compute the fingerprint, you must use this method for very large text
/// </summary>
/// <param name="source">String to compute</param>
/// <returns>Hash key</returns>
public static UInt64 ComputeFingerPrint(ref string source)
{
return ComputeFingerPrint(source);
}
/// <summary>
/// Compute the fingerprint, you must use this method for very large binary data
/// </summary>
/// <param name="source">Data to compute</param>
/// <returns>Hash key</returns>
public static UInt64 ComputeFingerPrint(ref byte[] source)
{
UInt64[] values = new UInt64[source.LongLength];
ConvertBytes(ref source, ref values);
return Compute(values);
}
/// <summary>
/// Compute the fingerprint, you must use this method for very large binary data
/// </summary>
/// <param name="source">Data to compute</param>
/// <returns>Hash key</returns>
public static UInt64 ComputeFingerPrint(byte[] source)
{
return ComputeFingerPrint(ref source);
}
/// <summary>
/// Compute byte array to Uint64 array
/// </summary>
/// <param name="source">Table de byte source</param>
/// <param name="destination">Tableau de Uin64</param>
private static void ConvertBytes(ref byte[] source, ref UInt64[] destination)
{
for (long i = 0; i < source.LongLength; i++)
destination[i] = Convert.ToUInt64(source[i]);
}
}
}
My VB code:
Imports RF
Module Module1
Sub Main()
Dim t As New RabinFingerprint
End Sub
End Module

If you want to use instances, you need to add a non-static constructor to the C# class - currently it's only got a static constructor.
There is info on diffs between static/shared in VB.Net and C# here that could be useful in resolving this.
If you were doing this in C# you just call the class's static methods like
UInt64 result = RabinFingerprint.ComputeFIngerprint(...);
etc.
In VB.Net this looks something like this:
Dim result = RF.RabinFingerprint.ComputeFingerprint(...)
Here is an example from MSDN of what I mean. Here both Console.WriteLine and Regex.Split are static, just like your class's methods.
Dim input As String = "plum--pear"
Dim pattern As String = "-" ' Split on hyphens
Dim substrings() As String = Regex.Split(input, pattern)
For Each match As String In substrings
Console.WriteLine("'{0}'", match)
Next
' The method writes the following to the console:
' 'plum'
' ''
' 'pear'

You have no constructors because your class is declared as static

Have you tried to use it from C#?
It probably gives you the same error there.
EDIT
I have tried your code. (Jeff we need a copy source code button)
IN VB.NET. There's the following error:
Type 'RF.RabinFingerprint' has no constructors.
In C# you get the following 2 errors.
Cannot create an instance of the static class 'RF.RabinFingerprint'
Cannot declare a variable of static type 'RF.RabinFingerprint'
Actually C# shows you the real problem. As Jazz have mentioned. You should change your class to be nonstatic to work properly
EDIT2
Steve is right. If your class has been designed to be static as it appears since everything in there is static, then what has to be changed is the call to the constructor. Since the class is static you can't create an instance of your class.
There is no need to call the constructor because it will be automatically called the first time the class is used (For example when you call a method from it).

"Chunked" MemoryStream

I'm looking for the implementation of MemoryStream which does not allocate memory as one big block, but rather a collection of chunks. I want to store a few GB of data in memory (64 bit) and avoid limitation of memory fragmentation.

Something like this:
class ChunkedMemoryStream : Stream
{
private readonly List<byte[]> _chunks = new List<byte[]>();
private int _positionChunk;
private int _positionOffset;
private long _position;
public override bool CanRead
{
get { return true; }
}
public override bool CanSeek
{
get { return true; }
}
public override bool CanWrite
{
get { return true; }
}
public override void Flush() { }
public override long Length
{
get { return _chunks.Sum(c => c.Length); }
}
public override long Position
{
get
{
return _position;
}
set
{
_position = value;
_positionChunk = 0;
while (_positionOffset != 0)
{
if (_positionChunk >= _chunks.Count)
throw new OverflowException();
if (_positionOffset < _chunks[_positionChunk].Length)
return;
_positionOffset -= _chunks[_positionChunk].Length;
_positionChunk++;
}
}
}
public override int Read(byte[] buffer, int offset, int count)
{
int result = 0;
while ((count != 0) && (_positionChunk != _chunks.Count))
{
int fromChunk = Math.Min(count, _chunks[_positionChunk].Length - _positionOffset);
if (fromChunk != 0)
{
Array.Copy(_chunks[_positionChunk], _positionOffset, buffer, offset, fromChunk);
offset += fromChunk;
count -= fromChunk;
result += fromChunk;
_position += fromChunk;
}
_positionOffset = 0;
_positionChunk++;
}
return result;
}
public override long Seek(long offset, SeekOrigin origin)
{
long newPos = 0;
switch (origin)
{
case SeekOrigin.Begin:
newPos = offset;
break;
case SeekOrigin.Current:
newPos = Position + offset;
break;
case SeekOrigin.End:
newPos = Length - offset;
break;
}
Position = Math.Max(0, Math.Min(newPos, Length));
return newPos;
}
public override void SetLength(long value)
{
throw new NotImplementedException();
}
public override void Write(byte[] buffer, int offset, int count)
{
while ((count != 0) && (_positionChunk != _chunks.Count))
{
int toChunk = Math.Min(count, _chunks[_positionChunk].Length - _positionOffset);
if (toChunk != 0)
{
Array.Copy(buffer, offset, _chunks[_positionChunk], _positionOffset, toChunk);
offset += toChunk;
count -= toChunk;
_position += toChunk;
}
_positionOffset = 0;
_positionChunk++;
}
if (count != 0)
{
byte[] chunk = new byte[count];
Array.Copy(buffer, offset, chunk, 0, count);
_chunks.Add(chunk);
_positionChunk = _chunks.Count;
_position += count;
}
}
}
class Program
{
static void Main(string[] args)
{
ChunkedMemoryStream cms = new ChunkedMemoryStream();
Debug.Assert(cms.Length == 0);
Debug.Assert(cms.Position == 0);
cms.Position = 0;
byte[] helloworld = Encoding.UTF8.GetBytes("hello world");
cms.Write(helloworld, 0, 3);
cms.Write(helloworld, 3, 3);
cms.Write(helloworld, 6, 5);
Debug.Assert(cms.Length == 11);
Debug.Assert(cms.Position == 11);
cms.Position = 0;
byte[] b = new byte[20];
cms.Read(b, 3, (int)cms.Length);
Debug.Assert(b.Skip(3).Take(11).SequenceEqual(helloworld));
cms.Position = 0;
cms.Write(Encoding.UTF8.GetBytes("seeya"), 0, 5);
Debug.Assert(cms.Length == 11);
Debug.Assert(cms.Position == 5);
cms.Position = 0;
cms.Read(b, 0, (byte) cms.Length);
Debug.Assert(b.Take(11).SequenceEqual(Encoding.UTF8.GetBytes("seeya world")));
Debug.Assert(cms.Length == 11);
Debug.Assert(cms.Position == 11);
cms.Write(Encoding.UTF8.GetBytes(" again"), 0, 6);
Debug.Assert(cms.Length == 17);
Debug.Assert(cms.Position == 17);
cms.Position = 0;
cms.Read(b, 0, (byte)cms.Length);
Debug.Assert(b.Take(17).SequenceEqual(Encoding.UTF8.GetBytes("seeya world again")));
}
}

You need to first determine if virtual address fragmentation is the problem.
If you are on a 64 bit machine (which you seem to indicate you are) I seriously doubt it is. Each 64 bit process has almost the the entire 64 bit virtual memory space available and your only worry is virtual address space fragmentation not physical memory fragmentation (which is what the operating system must worry about). The OS memory manager already pages memory under the covers. For the forseeable future you will not run out of virtual address space before you run out of physical memory. This is unlikely change before we both retire.
If you are have a 32 bit address space, then allocating contiguous large blocks of memory in the GB ramge you will encounter a fragmentation problem quite quickly. There is no stock chunk allocating memory stream in the CLR. There is one in the under the covers in ASP.NET (for other reasons) but it is not accessable. If you must travel this path you are probably better off writing one youself anyway because the usage pattern of your application is unlikely to be similar to many others and trying to fit your data into a 32bit address space will likely be your perf bottleneck.
I highly recommend requiring a 64 bit process if you are manipulating GBs of data. It will do a much better job than hand-rolled solutions to 32 bit address space fragmentation regardless of how cleaver you are.

The Bing team has released RecyclableMemoryStream and wrote about it here. The benefits they cite are:
Eliminate Large Object Heap allocations by using pooled buffers
Incur far fewer gen 2 GCs, and spend far less time paused due to GC
Avoid memory leaks by having a bounded pool size
Avoid memory fragmentation
Provide excellent debuggability
Provide metrics for performance tracking

I've found similar problem in my application. I've read large amount of compressed data and I suffered from OutOfMemoryException using MemoryStream. I've written my own implementation of "chunked" memory stream based on collection of byte arrays. If you have any idea how to make this memory stream more effective, please write me about it.
public sealed class ChunkedMemoryStream : Stream
{
#region Constants
private const int BUFFER_LENGTH = 65536;
private const byte ONE = 1;
private const byte ZERO = 0;
#endregion
#region Readonly & Static Fields
private readonly Collection<byte[]> _chunks;
#endregion
#region Fields
private long _length;
private long _position;
private const byte TWO = 2;
#endregion
#region C'tors
public ChunkedMemoryStream()
{
_chunks = new Collection<byte[]> { new byte[BUFFER_LENGTH], new byte[BUFFER_LENGTH] };
_position = ZERO;
_length = ZERO;
}
#endregion
#region Instance Properties
public override bool CanRead
{
get { return true; }
}
public override bool CanSeek
{
get { return true; }
}
public override bool CanWrite
{
get { return true; }
}
public override long Length
{
get { return _length; }
}
public override long Position
{
get { return _position; }
set
{
if (!CanSeek)
throw new NotSupportedException();
_position = value;
if (_position > _length)
_position = _length - ONE;
}
}
private byte[] CurrentChunk
{
get
{
long positionDividedByBufferLength = _position / BUFFER_LENGTH;
var chunkIndex = Convert.ToInt32(positionDividedByBufferLength);
byte[] chunk = _chunks[chunkIndex];
return chunk;
}
}
private int PositionInChunk
{
get
{
int positionInChunk = Convert.ToInt32(_position % BUFFER_LENGTH);
return positionInChunk;
}
}
private int RemainingBytesInCurrentChunk
{
get
{
Contract.Ensures(Contract.Result<int>() > ZERO);
int remainingBytesInCurrentChunk = CurrentChunk.Length - PositionInChunk;
return remainingBytesInCurrentChunk;
}
}
#endregion
#region Instance Methods
public override void Flush()
{
}
public override int Read(byte[] buffer, int offset, int count)
{
if (offset + count > buffer.Length)
throw new ArgumentException();
if (buffer == null)
throw new ArgumentNullException();
if (offset < ZERO || count < ZERO)
throw new ArgumentOutOfRangeException();
if (!CanRead)
throw new NotSupportedException();
int bytesToRead = count;
if (_length - _position < bytesToRead)
bytesToRead = Convert.ToInt32(_length - _position);
int bytesreaded = 0;
while (bytesToRead > ZERO)
{
// get remaining bytes in current chunk
// read bytes in current chunk
// advance to next position
int remainingBytesInCurrentChunk = RemainingBytesInCurrentChunk;
if (remainingBytesInCurrentChunk > bytesToRead)
remainingBytesInCurrentChunk = bytesToRead;
Array.Copy(CurrentChunk, PositionInChunk, buffer, offset, remainingBytesInCurrentChunk);
//move position in source
_position += remainingBytesInCurrentChunk;
//move position in target
offset += remainingBytesInCurrentChunk;
//bytesToRead is smaller
bytesToRead -= remainingBytesInCurrentChunk;
//count readed bytes;
bytesreaded += remainingBytesInCurrentChunk;
}
return bytesreaded;
}
public override long Seek(long offset, SeekOrigin origin)
{
switch (origin)
{
case SeekOrigin.Begin:
Position = offset;
break;
case SeekOrigin.Current:
Position += offset;
break;
case SeekOrigin.End:
Position = Length + offset;
break;
}
return Position;
}
private long Capacity
{
get
{
int numberOfChunks = _chunks.Count;
long capacity = numberOfChunks * BUFFER_LENGTH;
return capacity;
}
}
public override void SetLength(long value)
{
if (value > _length)
{
while (value > Capacity)
{
var item = new byte[BUFFER_LENGTH];
_chunks.Add(item);
}
}
else if (value < _length)
{
var decimalValue = Convert.ToDecimal(value);
var valueToBeCompared = decimalValue % BUFFER_LENGTH == ZERO ? Capacity : Capacity - BUFFER_LENGTH;
//remove data chunks, but leave at least two chunks
while (value < valueToBeCompared && _chunks.Count > TWO)
{
byte[] lastChunk = _chunks.Last();
_chunks.Remove(lastChunk);
}
}
_length = value;
if (_position > _length - ONE)
_position = _length == 0 ? ZERO : _length - ONE;
}
public override void Write(byte[] buffer, int offset, int count)
{
if (!CanWrite)
throw new NotSupportedException();
int bytesToWrite = count;
while (bytesToWrite > ZERO)
{
//get remaining space in current chunk
int remainingBytesInCurrentChunk = RemainingBytesInCurrentChunk;
//if count of bytes to be written is fewer than remaining
if (remainingBytesInCurrentChunk > bytesToWrite)
remainingBytesInCurrentChunk = bytesToWrite;
//if remaining bytes is still greater than zero
if (remainingBytesInCurrentChunk > ZERO)
{
//write remaining bytes to current Chunk
Array.Copy(buffer, offset, CurrentChunk, PositionInChunk, remainingBytesInCurrentChunk);
//change offset of source array
offset += remainingBytesInCurrentChunk;
//change bytes to write
bytesToWrite -= remainingBytesInCurrentChunk;
//change length and position
_length += remainingBytesInCurrentChunk;
_position += remainingBytesInCurrentChunk;
}
if (Capacity == _position)
_chunks.Add(new byte[BUFFER_LENGTH]);
}
}
/// <summary>
/// Gets entire content of stream regardless of Position value and return output as byte array
/// </summary>
/// <returns>byte array</returns>
public byte[] ToArray()
{
var outputArray = new byte[Length];
if (outputArray.Length != ZERO)
{
long outputPosition = ZERO;
foreach (byte[] chunk in _chunks)
{
var remainingLength = (Length - outputPosition) > chunk.Length
? chunk.Length
: Length - outputPosition;
Array.Copy(chunk, ZERO, outputArray, outputPosition, remainingLength);
outputPosition = outputPosition + remainingLength;
}
}
return outputArray;
}
/// <summary>
/// Method set Position to first element and write entire stream to another
/// </summary>
/// <param name="stream">Target stream</param>
public void WriteTo(Stream stream)
{
Contract.Requires(stream != null);
Position = ZERO;
var buffer = new byte[BUFFER_LENGTH];
int bytesReaded;
do
{
bytesReaded = Read(buffer, ZERO, BUFFER_LENGTH);
stream.Write(buffer, ZERO, bytesReaded);
} while (bytesReaded > ZERO);
}
#endregion
}

Here is a full implementation:
/// <summary>
/// Defines a MemoryStream that does not sit on the Large Object Heap, thus avoiding memory fragmentation.
/// </summary>
/// <seealso cref="Stream" />
public sealed class ChunkedMemoryStream : Stream
{
/// <summary>
/// Defines the default chunk size. Currently defined as 0x10000.
/// </summary>
public const int DefaultChunkSize = 0x10000; // needs to be < 85000
private const int _lohSize = 85000;
private List<byte[]> _chunks = new List<byte[]>();
private long _position;
private int _chunkSize;
private int _lastChunkPos;
private int _lastChunkPosIndex;
/// <summary>
/// Initializes a new instance of the <see cref="ChunkedMemoryStream" /> class based on the specified byte array.
/// </summary>
/// <param name="chunkSize">Size of the underlying chunks.</param>
/// <param name="buffer">The array of unsigned bytes from which to create the current stream.</param>
public ChunkedMemoryStream(int chunkSize = DefaultChunkSize, byte[] buffer = null)
{
FreeOnDispose = true;
ChunkSize = chunkSize;
_chunks.Add(new byte[chunkSize]);
if (buffer != null)
{
Write(buffer, 0, buffer.Length);
Position = 0;
}
}
/// <summary>
/// Gets or sets a value indicating whether to free the underlying chunks on dispose.
/// </summary>
/// <value>
/// <c>true</c> if the underlying chunks must be freed on disposal; otherwise, <c>false</c>.
/// </value>
public bool FreeOnDispose { get; set; }
/// <summary>
/// Releases the unmanaged resources used by the <see cref="Stream" /> and optionally releases the managed resources.
/// </summary>
/// <param name="disposing">true to release both managed and unmanaged resources; false to release only unmanaged resources.</param>
protected override void Dispose(bool disposing)
{
if (FreeOnDispose)
{
if (_chunks != null)
{
_chunks = null;
_chunkSize = 0;
_position = 0;
}
}
base.Dispose(disposing);
}
/// <summary>
/// When overridden in a derived class, clears all buffers for this stream and causes any buffered data to be written to the underlying device.
/// This implementation does nothing.
/// </summary>
public override void Flush()
{
// do nothing
}
/// <summary>
/// When overridden in a derived class, reads a sequence of bytes from the current stream and advances the position within the stream by the number of bytes read.
/// </summary>
/// <param name="buffer">An array of bytes. When this method returns, the buffer contains the specified byte array with the values between <paramref name="offset" /> and (<paramref name="offset" /> + <paramref name="count" /> - 1) replaced by the bytes read from the current source.</param>
/// <param name="offset">The zero-based byte offset in <paramref name="buffer" /> at which to begin storing the data read from the current stream.</param>
/// <param name="count">The maximum number of bytes to be read from the current stream.</param>
/// <returns>
/// The total number of bytes read into the buffer. This can be less than the number of bytes requested if that many bytes are not currently available, or zero (0) if the end of the stream has been reached.
/// </returns>
/// <exception cref="ArgumentNullException"><paramref name="buffer" /> is null.</exception>
/// <exception cref="ArgumentOutOfRangeException"><paramref name="offset" /> or <paramref name="count" /> is negative.</exception>
/// <exception cref="ArgumentException">The sum of <paramref name="offset" /> and <paramref name="count" /> is larger than the buffer length.</exception>
/// <exception cref="ObjectDisposedException">Methods were called after the stream was closed.</exception>
public override int Read(byte[] buffer, int offset, int count)
{
if (buffer == null)
throw new ArgumentNullException(nameof(buffer));
if (offset < 0)
throw new ArgumentOutOfRangeException(nameof(offset));
if (count < 0)
throw new ArgumentOutOfRangeException(nameof(count));
if ((buffer.Length - offset) < count)
throw new ArgumentException(null, nameof(count));
CheckDisposed();
var chunkIndex = (int)(_position / ChunkSize);
if (chunkIndex == _chunks.Count)
return 0;
var chunkPos = (int)(_position % ChunkSize);
count = (int)Math.Min(count, Length - _position);
if (count == 0)
return 0;
var left = count;
var inOffset = offset;
var total = 0;
do
{
var toCopy = Math.Min(left, ChunkSize - chunkPos);
Buffer.BlockCopy(_chunks[chunkIndex], chunkPos, buffer, inOffset, toCopy);
inOffset += toCopy;
left -= toCopy;
total += toCopy;
if ((chunkPos + toCopy) == ChunkSize)
{
if (chunkIndex == (_chunks.Count - 1))
{
// last chunk
break;
}
chunkPos = 0;
chunkIndex++;
}
else
{
chunkPos += toCopy;
}
}
while (left > 0);
_position += total;
return total;
}
/// <summary>
/// Reads a byte from the stream and advances the position within the stream by one byte, or returns -1 if at the end of the stream.
/// </summary>
/// <returns>
/// The unsigned byte cast to an Int32, or -1 if at the end of the stream.
/// </returns>
/// <exception cref="ObjectDisposedException">Methods were called after the stream was closed.</exception>
public override int ReadByte()
{
CheckDisposed();
if (_position >= Length)
return -1;
var ret = _chunks[(int)(_position / ChunkSize)][_position % ChunkSize];
_position++;
return ret;
}
/// <summary>
/// When overridden in a derived class, sets the position within the current stream.
/// </summary>
/// <param name="offset">A byte offset relative to the <paramref name="origin" /> parameter.</param>
/// <param name="origin">A value of type <see cref="SeekOrigin" /> indicating the reference point used to obtain the new position.</param>
/// <returns>The new position within the current stream.</returns>
/// <exception cref="ObjectDisposedException">Methods were called after the stream was closed.</exception>
public override long Seek(long offset, SeekOrigin origin)
{
CheckDisposed();
switch (origin)
{
case SeekOrigin.Begin:
Position = offset;
break;
case SeekOrigin.Current:
Position += offset;
break;
case SeekOrigin.End:
Position = Length + offset;
break;
}
return Position;
}
private void CheckDisposed()
{
if (_chunks == null)
throw new ObjectDisposedException(null, "Cannot access a disposed stream.");
}
/// <summary>
/// When overridden in a derived class, sets the length of the current stream.
/// </summary>
/// <param name="value">The desired length of the <paramref name="value" /> stream in bytes.</param>
/// <exception cref="ArgumentOutOfRangeException"><paramref name="value" /> is out of range.</exception>
/// <exception cref="ObjectDisposedException">Methods were called after the stream was closed.</exception>
public override void SetLength(long value)
{
CheckDisposed();
if (value < 0)
throw new ArgumentOutOfRangeException(nameof(value));
if (value > Length)
throw new ArgumentOutOfRangeException(nameof(value));
var needed = value / ChunkSize;
if ((value % ChunkSize) != 0)
{
needed++;
}
if (needed > int.MaxValue)
throw new ArgumentOutOfRangeException(nameof(value));
if (needed < _chunks.Count)
{
var remove = (int)(_chunks.Count - needed);
for (var i = 0; i < remove; i++)
{
_chunks.RemoveAt(_chunks.Count - 1);
}
}
_lastChunkPos = (int)(value % ChunkSize);
}
/// <summary>
/// Converts the current stream to a byte array.
/// </summary>
/// <returns>
/// An array of bytes
/// </returns>
public byte[] ToArray()
{
CheckDisposed();
var bytes = new byte[Length];
var offset = 0;
for (var i = 0; i < _chunks.Count; i++)
{
var count = (i == (_chunks.Count - 1)) ? _lastChunkPos : _chunks[i].Length;
if (count > 0)
{
Buffer.BlockCopy(_chunks[i], 0, bytes, offset, count);
offset += count;
}
}
return bytes;
}
/// <summary>
/// When overridden in a derived class, writes a sequence of bytes to the current stream and advances the current position within this stream by the number of bytes written.
/// </summary>
/// <param name="buffer">An array of bytes. This method copies <paramref name="count" /> bytes from <paramref name="buffer" /> to the current stream.</param>
/// <param name="offset">The zero-based byte offset in <paramref name="buffer" /> at which to begin copying bytes to the current stream.</param>
/// <param name="count">The number of bytes to be written to the current stream.</param>
/// <exception cref="ArgumentException">The sum of <paramref name="offset" /> and <paramref name="count" /> is greater than the buffer length.</exception>
/// <exception cref="ArgumentNullException"><paramref name="buffer" /> is null.</exception>
/// <exception cref="ArgumentOutOfRangeException"><paramref name="offset" /> or <paramref name="count" /> is negative.</exception>
/// <exception cref="ObjectDisposedException">Methods were called after the stream was closed.</exception>
public override void Write(byte[] buffer, int offset, int count)
{
if (buffer == null)
throw new ArgumentNullException(nameof(buffer));
if (offset < 0)
throw new ArgumentOutOfRangeException(nameof(offset));
if (count < 0)
throw new ArgumentOutOfRangeException(nameof(count));
if ((buffer.Length - offset) < count)
throw new ArgumentException(null, nameof(count));
CheckDisposed();
var chunkPos = (int)(_position % ChunkSize);
var chunkIndex = (int)(_position / ChunkSize);
if (chunkIndex == _chunks.Count)
{
_chunks.Add(new byte[ChunkSize]);
}
var left = count;
var inOffset = offset;
do
{
var copied = Math.Min(left, ChunkSize - chunkPos);
Buffer.BlockCopy(buffer, inOffset, _chunks[chunkIndex], chunkPos, copied);
inOffset += copied;
left -= copied;
if ((chunkPos + copied) == ChunkSize)
{
chunkIndex++;
chunkPos = 0;
if (chunkIndex == _chunks.Count)
{
_chunks.Add(new byte[ChunkSize]);
}
}
else
{
chunkPos += copied;
}
}
while (left > 0);
_position += count;
if (chunkIndex == (_chunks.Count - 1))
{
if (chunkIndex > _lastChunkPosIndex || (chunkIndex == _lastChunkPosIndex && chunkPos > _lastChunkPos))
{
_lastChunkPos = chunkPos;
_lastChunkPosIndex = chunkIndex;
}
}
}
/// <summary>
/// Writes a byte to the current position in the stream and advances the position within the stream by one byte.
/// </summary>
/// <param name="value">The byte to write to the stream.</param>
/// <exception cref="ObjectDisposedException">Methods were called after the stream was closed.</exception>
public override void WriteByte(byte value)
{
CheckDisposed();
var chunkIndex = (int)(_position / ChunkSize);
var chunkPos = (int)(_position % ChunkSize);
if (chunkPos > (ChunkSize - 1))
{
chunkIndex++;
chunkPos = 0;
if (chunkIndex == _chunks.Count)
{
_chunks.Add(new byte[ChunkSize]);
}
}
_chunks[chunkIndex][chunkPos++] = value;
_position++;
if (chunkIndex == (_chunks.Count - 1))
{
if (chunkIndex > _lastChunkPosIndex || (chunkIndex == _lastChunkPosIndex && chunkPos > _lastChunkPos))
{
_lastChunkPos = chunkPos;
_lastChunkPosIndex = chunkIndex;
}
}
}
/// <summary>
/// Writes to the specified stream.
/// </summary>
/// <param name="stream">The stream.</param>
/// <exception cref="ArgumentNullException"><paramref name="stream" /> is null.</exception>
public void WriteTo(Stream stream)
{
if (stream == null)
throw new ArgumentNullException(nameof(stream));
CheckDisposed();
for (var i = 0; i < _chunks.Count; i++)
{
var count = i == (_chunks.Count - 1) ? _lastChunkPos : _chunks[i].Length;
stream.Write(_chunks[i], 0, count);
}
}
/// <summary>
/// When overridden in a derived class, gets a value indicating whether the current stream supports reading.
/// </summary>
public override bool CanRead => true;
/// <summary>
/// When overridden in a derived class, gets a value indicating whether the current stream supports seeking.
/// </summary>
public override bool CanSeek => true;
/// <summary>
/// When overridden in a derived class, gets a value indicating whether the current stream supports writing.
/// </summary>
public override bool CanWrite => true;
/// <summary>
/// When overridden in a derived class, gets the length in bytes of the stream.
/// </summary>
/// <exception cref="ObjectDisposedException">Methods were called after the stream was closed.</exception>
public override long Length
{
get
{
CheckDisposed();
if (_chunks.Count == 0)
return 0;
return (long)(_chunks.Count - 1) * ChunkSize + _lastChunkPos;
}
}
/// <summary>
/// Gets or sets the size of the underlying chunks. Cannot be greater than or equal to 85000.
/// </summary>
/// <value>
/// The chunks size.
/// </value>
/// <exception cref="ArgumentOutOfRangeException"><paramref name="value" /> is out of range.</exception>
public int ChunkSize
{
get => _chunkSize;
set
{
if (value <= 0 || value >= _lohSize)
throw new ArgumentOutOfRangeException(nameof(value));
_chunkSize = value;
}
}
/// <summary>
/// When overridden in a derived class, gets or sets the position within the current stream.
/// </summary>
/// <exception cref="ArgumentOutOfRangeException"><paramref name="value" /> is out of range.</exception>
/// <exception cref="ObjectDisposedException">Methods were called after the stream was closed.</exception>
public override long Position
{
get
{
CheckDisposed();
return _position;
}
set
{
CheckDisposed();
if (value < 0)
throw new ArgumentOutOfRangeException(nameof(value));
if (value > Length)
throw new ArgumentOutOfRangeException(nameof(value));
_position = value;
}
}
}

You should use the UnmanagedMemoryStream when dealing with over 2GB chunks of memory, as MemoryStream is limited to 2GB, and the UnmanagedMemoryStream was made to deal with this problem.

SparseMemoryStream does this in .NET it's in buried deep down in an internal class library though -- the source code is available of course, since Microsoft put it all out there as open source.
You can grab the code for it here: http://www.dotnetframework.org/default.aspx/4#0/4#0/DEVDIV_TFS/Dev10/Releases/RTMRel/wpf/src/Base/MS/Internal/IO/Packaging/SparseMemoryStream#cs/1305600/SparseMemoryStream#cs
That being said, I highly recommend not using it as is -- At the very least remove all the calls to IsolatedStorage for starters, as this seems to be the cause of no end of bugs* in the framework's packaging API.
(*: In addition to spreading the data around in streams, if it gets too big, it basically reinvents swap files for some reason -- in the user's Isolated Storage no less -- and coincidentally, most MS products that allow for .NET based add-ins do not have their app domains setup in such a way that you can access Isolated Storage -- VSTO add-ins are notorious for suffering from this issue, for example.)

Another implementation of chunked stream could be considered as a stock MemoryStream replacement. Additionally it allows to allocate a single large byte array on LOH which will be used as a "chunk" pool, shared between all ChunkedStream instances...
https://github.com/ImmortalGAD/ChunkedStream