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Convert 2 successive Bytes to one int value Increase speed in C#

I need to combine two Bytes into one int value.
I receive from my camera a 16bit Image were two successive bytes have the intensity value of one pixel. My goal is to combine these two bytes into one "int" vale.
I manage to do this using the following code:
for (int i = 0; i < VectorLength * 2; i = i + 2)
{
NewImageVector[ImagePointer] = ((int)(buffer.Array[i + 1]) << 8) | ((int)(buffer.Array[i]));
ImagePointer++;
}
My image is 1280*960 so VectorLength==1228800 and the incomming buffer size is 2*1228800=2457600 elements...
Is there any way that I can speed this up?
Maybe there is another way so I don't need to use a for-loop.
Thank you

You could use the equivalent to the union of c. Im not sure if faster, but more elegant:
[StructLayout(LayoutKind.Explicit)]
struct byte_array
{
[FieldOffset(0)]
public byte byte1;
[FieldOffset(1)]
public byte byte2;
[FieldOffset(0)]
public short int0;
}
use it like this:
byte_array ba = new byte_array();
//insert the two bytes
ba.byte1 = (byte)(buffer.Array[i]);
ba.byte2 = (byte)(buffer.Array[i + 1]);
//get the integer
NewImageVector[ImagePointer] = ba.int1;
You can fill your two bytes and use the int. To find the faster way take the StopWatch-Class and compare the two ways like this:
Stopwatch stopWatch = new Stopwatch();
stopWatch.Start();
//The code
stopWatch.Stop();
MessageBox.Show(stopWatch.ElapsedTicks.ToString()); //Or milliseconds ,...

Assuming you can (re-)define NewImageVector as a short[], and every two consecutive bytes in Buffer should be transformed into a short (which basically what you're doing now, only you cast to an int afterwards), you can use Buffer.BlockCopy to do it for you.
As the documentation tells, you Buffer.BlockCopy copies bytes from one array to another, so in order to copy your bytes in buffer you need to do the following:
Buffer.BlockCopy(Buffer, 0, NewImageVector, 0, [NumberOfExpectedShorts] * 2)
This tells BlockCopy that you want to start copying bytes from Buffer, starting at index 0, to NewImageVector starting at index 0, and you want to copy [NumberOfExpectedShorts] * 2 bytes (since every short is two bytes long).
No loops, but it does depend on the ability of using a short[] array instead of an int[] array (and indeed, on using an array to begin with).
Note that this also requires the bytes in Buffer to be in little-endian order (i.e. Buffer[index] contains the low byte, buffer[index + 1] the high byte).

You can achieve a small performance increase by using unsafe pointers to iterate the arrays. The following code assumes that source is the input byte array (buffer.Array in your case). It also assumes that source has an even number of elements. In production code you would obviously have to check these things.
int[] output = new int[source.Length / 2];
fixed (byte* pSource = source)
fixed (int* pDestination = output)
{
byte* sourceIterator = pSource;
int* destIterator = pDestination;
for (int i = 0; i < output.Length; i++)
{
(*destIterator) = ((*sourceIterator) | (*(sourceIterator + 1) << 8));
destIterator++;
sourceIterator += 2;
}
}
return output;

PadRight() isn't padding at all

I'm trying to use the String.PadRight method in C#, but it's just not doing anything with the string.
Code:
int strlen = 4 - (data.Length % 4);
char pad = '=';
string datapad = data.PadRight(strlen, pad);
The string in question is Base64 encoded data, and I need the '=' at the end to pad it for ConvertFromBase64 to work properly.
eyJhbGciOiJSUzI1NiIsImtpZCI6IjY5NDZmZjNlZGUyOTk3ZWExMmVhMDRlNGFhNjYyOWRjZWVhZWZhOTAifQ

strlen must be greater than the length of data in order for it to pad it. As Grant Winney points out, PadRight takes the total width of the string, and not just the number of times you'd like to repeat that character at the end of it.
In the code below, strlen will always be less than or equal to 4, which is a lot less than the length of your base 64 encoded string.
int strlen = 4 - (data.Length % 4);
So really you might want to do this instead:
int strlen = 4 - (data.Length % 4) + data.Length;
Or just:
string datapad = data.PadRight(strlen + data.Length, pad);

File Transfer from one system to another in c#

I Have this c# program which is a client receives the file from the server. Sometimes it works seamlessly. and sometimes it gives an exception in fileName = Encoding.ASCII.GetString(dataByte, 4, fileNameLen);.
ArgumentOutOfRange Exception
Index and count must refer to a location within the buffer.
Parameter name: bytes
If the value of fileNameLen is 8 or 12 then it works properly. Otherwise it will be 1330795077. Why is that? Can anyone explain me why is this? please. Here is my code.
string fileName = string.Empty;
int thisRead = 0;
int blockSize = 1024;
Byte[] dataByte = new Byte[blockSize];
lock (this)
{
string folderPath = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments)+"\\";
ns.Read(dataByte, thisRead, blockSize);
int fileNameLen = BitConverter.ToInt32(dataByte, 0);
fileName = Encoding.ASCII.GetString(dataByte, 4, fileNameLen);
Stream fileStream = File.OpenWrite(folderPath + fileName);
fileStream.Write(dataByte, 4 + fileNameLen, (1024 - (4 + fileNameLen)));
while (true)
{
thisRead = ns.Read(dataByte, 0, blockSize);
fileStream.Write(dataByte, 0, thisRead);
if (thisRead == 0)
break;
}
fileStream.Close();
}

index and count do not denote a valid range in bytes.
Encoding.ASCII.GetString()
ArgumentOutOfRangeException is thrown beacuse of on the following reasons:
index or count is less than zero.
index and count do not denote a valid range in bytes.
Count is in your case: fileNameLen
The Documentation states:
Data to be converted, such as data read from a stream, can be
available only in sequential blocks. In this case, or if the amount of
data is so large that it needs to be divided into smaller blocks, the
application should use the Decoder or the Encoder provided by the
GetDecoder method or the GetEncoder method, respectively.
See Documentation

You would need to check on the contents of dataByte when it has been transferred. If you trying to create and integer from dataByte and you convert this to Int32 in fileNameLen you might receive silly values like 1330795077 and this is no valid index to Encoding.ASCII.GetString(dataByte, 4, fileNameLen);

in your code ns.Read(dataByte, thisRead, blockSize); should return an int value indicates the actual length read. Use that return value to control how many bytes you want to convert to string to avoid creating silly values.

Convert int32 to string in base 16

I'm currently trying to convert a .NET JSON Encoder to NETMF but have hit a problem with Convert.ToString() as there isn't such thing in NETMF.
The original line of the encoder looks like this:
Convert.ToString(codepoint, 16);
And after looking at the documentation for Convert.ToString(Int32, Int32) it says it's for converting an int32 into int 2, 8, 10 or 16 by providing the int as the first parameter and the base as the second.
What are some low level code of how to do this or how would I go about doing this?
As you can see from the code, I only need conversion from an Int32 to Int16.
EDIT
Ah, the encoder also then wants to do:
PadLeft(4, '0');
on the string, is this just adding 4 '0' + '0' + '0' + '0' to the start of the string?

If you mean you want to change a 32-bit integer value into a string which shows the value in hexadecimal:
string hex = intValue.ToString("x");
For variations, please see Stack Overflow question Convert a number into the hex value in .NET.
Disclaimer: I'm not sure if this function exists in NETMF, but it is so fundamental that I think it should.

Here’s some sample code for converting an integer to hexadecimal (base 16):
int num = 48764; // assign your number
// Generate hexadecimal number in reverse.
var sb = new StringBuilder();
do
{
sb.Append(hexChars[num & 15]);
num >>= 4;
}
while (num > 0);
// Pad with leading 0s for a minimum length of 4 characters.
while (sb.Length < 4)
sb.Append('0');
// Reverse string and get result.
char[] chars = new char[sb.Length];
sb.CopyTo(0, chars, 0, sb.Length);
Array.Reverse(chars);
string result = new string(chars);
PadLeft(4, '0') prepends leading 0s to the string to ensure a minimum length of 4 characters.
The hexChars value lookup may be trivially defined as a string:
internal static readonly string hexChars = "0123456789ABCDEF";
Edit: Replacing StringBuilder with List<char>:
// Generate hexadecimal number in reverse.
List<char> builder = new List<char>();
do
{
builder.Add(hexChars[num & 15]);
num >>= 4;
}
while (num > 0);
// Pad with leading 0s for a minimum length of 4 characters.
while (builder.Count < 4)
builder.Add('0');
// Reverse string and get result.
char[] chars = new char[builder.Count];
for (int i = 0; i < builder.Count; ++i)
chars[i] = builder[builder.Count - i - 1];
string result = new string(chars);
Note: Refer to the “Hexadecimal Number Output” section of Expert .NET Micro Framework for a discussion of this conversion.

What is the equivalent of memset in C#?

I need to fill a byte[] with a single non-zero value. How can I do this in C# without looping through each byte in the array?
Update: The comments seem to have split this into two questions -
Is there a Framework method to fill a byte[] that might be akin to memset
What is the most efficient way to do it when we are dealing with a very large array?
I totally agree that using a simple loop works just fine, as Eric and others have pointed out. The point of the question was to see if I could learn something new about C# :) I think Juliet's method for a Parallel operation should be even faster than a simple loop.
Benchmarks:
Thanks to Mikael Svenson: http://techmikael.blogspot.com/2009/12/filling-array-with-default-value.html
It turns out the simple for loop is the way to go unless you want to use unsafe code.
Apologies for not being clearer in my original post. Eric and Mark are both correct in their comments; need to have more focused questions for sure. Thanks for everyone's suggestions and responses.

You could use Enumerable.Repeat:
byte[] a = Enumerable.Repeat((byte)10, 100).ToArray();
The first parameter is the element you want repeated, and the second parameter is the number of times to repeat it.
This is OK for small arrays but you should use the looping method if you are dealing with very large arrays and performance is a concern.

Actually, there is little known IL operation called Initblk (English version) which does exactly that. So, let's use it as a method that doesn't require "unsafe". Here's the helper class:
public static class Util
{
static Util()
{
var dynamicMethod = new DynamicMethod("Memset", MethodAttributes.Public | MethodAttributes.Static, CallingConventions.Standard,
null, new [] { typeof(IntPtr), typeof(byte), typeof(int) }, typeof(Util), true);
var generator = dynamicMethod.GetILGenerator();
generator.Emit(OpCodes.Ldarg_0);
generator.Emit(OpCodes.Ldarg_1);
generator.Emit(OpCodes.Ldarg_2);
generator.Emit(OpCodes.Initblk);
generator.Emit(OpCodes.Ret);
MemsetDelegate = (Action<IntPtr, byte, int>)dynamicMethod.CreateDelegate(typeof(Action<IntPtr, byte, int>));
}
public static void Memset(byte[] array, byte what, int length)
{
var gcHandle = GCHandle.Alloc(array, GCHandleType.Pinned);
MemsetDelegate(gcHandle.AddrOfPinnedObject(), what, length);
gcHandle.Free();
}
public static void ForMemset(byte[] array, byte what, int length)
{
for(var i = 0; i < length; i++)
{
array[i] = what;
}
}
private static Action<IntPtr, byte, int> MemsetDelegate;
}
And what is the performance? Here's my result for Windows/.NET and Linux/Mono (different PCs).
Mono/for: 00:00:01.1356610
Mono/initblk: 00:00:00.2385835
.NET/for: 00:00:01.7463579
.NET/initblk: 00:00:00.5953503
So it's worth considering. Note that the resulting IL will not be verifiable.

Building on Lucero's answer, here is a faster version. It will double the number of bytes copied using Buffer.BlockCopy every iteration. Interestingly enough, it outperforms it by a factor of 10 when using relatively small arrays (1000), but the difference is not that large for larger arrays (1000000), it is always faster though. The good thing about it is that it performs well even down to small arrays. It becomes faster than the naive approach at around length = 100. For a one million element byte array, it was 43 times faster.
(tested on Intel i7, .Net 2.0)
public static void MemSet(byte[] array, byte value) {
if (array == null) {
throw new ArgumentNullException("array");
}
int block = 32, index = 0;
int length = Math.Min(block, array.Length);
//Fill the initial array
while (index < length) {
array[index++] = value;
}
length = array.Length;
while (index < length) {
Buffer.BlockCopy(array, 0, array, index, Math.Min(block, length-index));
index += block;
block *= 2;
}
}

A little bit late, but the following approach might be a good compromise without reverting to unsafe code. Basically it initializes the beginning of the array using a conventional loop and then reverts to Buffer.BlockCopy(), which should be as fast as you can get using a managed call.
public static void MemSet(byte[] array, byte value) {
if (array == null) {
throw new ArgumentNullException("array");
}
const int blockSize = 4096; // bigger may be better to a certain extent
int index = 0;
int length = Math.Min(blockSize, array.Length);
while (index < length) {
array[index++] = value;
}
length = array.Length;
while (index < length) {
Buffer.BlockCopy(array, 0, array, index, Math.Min(blockSize, length-index));
index += blockSize;
}
}

Looks like System.Runtime.CompilerServices.Unsafe.InitBlock now does the same thing as the OpCodes.Initblk instruction that Konrad's answer mentions (he also mentioned a source link).
The code to fill in the array is as follows:
byte[] a = new byte[N];
byte valueToFill = 255;
System.Runtime.CompilerServices.Unsafe.InitBlock(ref a[0], valueToFill, (uint) a.Length);

This simple implementation uses successive doubling, and performs quite well (about 3-4 times faster than the naive version according to my benchmarks):
public static void Memset<T>(T[] array, T elem)
{
int length = array.Length;
if (length == 0) return;
array[0] = elem;
int count;
for (count = 1; count <= length/2; count*=2)
Array.Copy(array, 0, array, count, count);
Array.Copy(array, 0, array, count, length - count);
}
Edit: upon reading the other answers, it seems I'm not the only one with this idea. Still, I'm leaving this here, since it's a bit cleaner and it performs on par with the others.

If performance is critical, you could consider using unsafe code and working directly with a pointer to the array.
Another option could be importing memset from msvcrt.dll and use that. However, the overhead from invoking that might easily be larger than the gain in speed.

Or use P/Invoke way:
[DllImport("msvcrt.dll",
EntryPoint = "memset",
CallingConvention = CallingConvention.Cdecl,
SetLastError = false)]
public static extern IntPtr MemSet(IntPtr dest, int c, int count);
static void Main(string[] args)
{
byte[] arr = new byte[3];
GCHandle gch = GCHandle.Alloc(arr, GCHandleType.Pinned);
MemSet(gch.AddrOfPinnedObject(), 0x7, arr.Length);
}

With the advent of Span<T> (which is dotnet core only, but it is the future of dotnet) you have yet another way of solving this problem:
var array = new byte[100];
var span = new Span<byte>(array);
span.Fill(255);

If performance is absolutely critical, then Enumerable.Repeat(n, m).ToArray() will be too slow for your needs. You might be able to crank out faster performance using PLINQ or Task Parallel Library:
using System.Threading.Tasks;
// ...
byte initialValue = 20;
byte[] data = new byte[size]
Parallel.For(0, size, index => data[index] = initialValue);

All answers are writing single bytes only - what if you want to fill a byte array with words? Or floats? I find use for that now and then. So after having written similar code to 'memset' in a non-generic way a few times and arriving at this page to find good code for single bytes, I went about writing the method below.
I think PInvoke and C++/CLI each have their drawbacks. And why not have the runtime 'PInvoke' for you into mscorxxx? Array.Copy and Buffer.BlockCopy are native code certainly. BlockCopy isn't even 'safe' - you can copy a long halfway over another, or over a DateTime as long as they're in arrays.
At least I wouldn't go file new C++ project for things like this - it's a waste of time almost certainly.
So here's basically an extended version of the solutions presented by Lucero and TowerOfBricks that can be used to memset longs, ints, etc as well as single bytes.
public static class MemsetExtensions
{
static void MemsetPrivate(this byte[] buffer, byte[] value, int offset, int length) {
var shift = 0;
for (; shift < 32; shift++)
if (value.Length == 1 << shift)
break;
if (shift == 32 || value.Length != 1 << shift)
throw new ArgumentException(
"The source array must have a length that is a power of two and be shorter than 4GB.", "value");
int remainder;
int count = Math.DivRem(length, value.Length, out remainder);
var si = 0;
var di = offset;
int cx;
if (count < 1)
cx = remainder;
else
cx = value.Length;
Buffer.BlockCopy(value, si, buffer, di, cx);
if (cx == remainder)
return;
var cachetrash = Math.Max(12, shift); // 1 << 12 == 4096
si = di;
di += cx;
var dx = offset + length;
// doubling up to 1 << cachetrash bytes i.e. 2^12 or value.Length whichever is larger
for (var al = shift; al <= cachetrash && di + (cx = 1 << al) < dx; al++) {
Buffer.BlockCopy(buffer, si, buffer, di, cx);
di += cx;
}
// cx bytes as long as it fits
for (; di + cx <= dx; di += cx)
Buffer.BlockCopy(buffer, si, buffer, di, cx);
// tail part if less than cx bytes
if (di < dx)
Buffer.BlockCopy(buffer, si, buffer, di, dx - di);
}
}
Having this you can simply add short methods to take the value type you need to memset with and call the private method, e.g. just find replace ulong in this method:
public static void Memset(this byte[] buffer, ulong value, int offset, int count) {
var sourceArray = BitConverter.GetBytes(value);
MemsetPrivate(buffer, sourceArray, offset, sizeof(ulong) * count);
}
Or go silly and do it with any type of struct (although the MemsetPrivate above only works for structs that marshal to a size that is a power of two):
public static void Memset<T>(this byte[] buffer, T value, int offset, int count) where T : struct {
var size = Marshal.SizeOf<T>();
var ptr = Marshal.AllocHGlobal(size);
var sourceArray = new byte[size];
try {
Marshal.StructureToPtr<T>(value, ptr, false);
Marshal.Copy(ptr, sourceArray, 0, size);
} finally {
Marshal.FreeHGlobal(ptr);
}
MemsetPrivate(buffer, sourceArray, offset, count * size);
}
I changed the initblk mentioned before to take ulongs to compare performance with my code and that silently fails - the code runs but the resulting buffer contains the least significant byte of the ulong only.
Nevertheless I compared the performance writing as big a buffer with for, initblk and my memset method. The times are in ms total over 100 repetitions writing 8 byte ulongs whatever how many times fit the buffer length. The for version is manually loop-unrolled for the 8 bytes of a single ulong.
Buffer Len #repeat For millisec Initblk millisec Memset millisec
0x00000008 100 For 0,0032 Initblk 0,0107 Memset 0,0052
0x00000010 100 For 0,0037 Initblk 0,0102 Memset 0,0039
0x00000020 100 For 0,0032 Initblk 0,0106 Memset 0,0050
0x00000040 100 For 0,0053 Initblk 0,0121 Memset 0,0106
0x00000080 100 For 0,0097 Initblk 0,0121 Memset 0,0091
0x00000100 100 For 0,0179 Initblk 0,0122 Memset 0,0102
0x00000200 100 For 0,0384 Initblk 0,0123 Memset 0,0126
0x00000400 100 For 0,0789 Initblk 0,0130 Memset 0,0189
0x00000800 100 For 0,1357 Initblk 0,0153 Memset 0,0170
0x00001000 100 For 0,2811 Initblk 0,0167 Memset 0,0221
0x00002000 100 For 0,5519 Initblk 0,0278 Memset 0,0274
0x00004000 100 For 1,1100 Initblk 0,0329 Memset 0,0383
0x00008000 100 For 2,2332 Initblk 0,0827 Memset 0,0864
0x00010000 100 For 4,4407 Initblk 0,1551 Memset 0,1602
0x00020000 100 For 9,1331 Initblk 0,2768 Memset 0,3044
0x00040000 100 For 18,2497 Initblk 0,5500 Memset 0,5901
0x00080000 100 For 35,8650 Initblk 1,1236 Memset 1,5762
0x00100000 100 For 71,6806 Initblk 2,2836 Memset 3,2323
0x00200000 100 For 77,8086 Initblk 2,1991 Memset 3,0144
0x00400000 100 For 131,2923 Initblk 4,7837 Memset 6,8505
0x00800000 100 For 263,2917 Initblk 16,1354 Memset 33,3719
I excluded the first call every time, since both initblk and memset take a hit of I believe it was about .22ms for the first call. Slightly surprising my code is faster for filling short buffers than initblk, seeing it got half a page full of setup code.
If anybody feels like optimizing this, go ahead really. It's possible.

Tested several ways, described in different answers.
See sources of test in c# test class

You could do it when you initialize the array but I don't think that's what you are asking for:
byte[] myBytes = new byte[5] { 1, 1, 1, 1, 1};

.NET Core has a built-in Array.Fill() function, but sadly .NET Framework is missing it. .NET Core has two variations: fill the entire array and fill a portion of the array starting at an index.
Building on the ideas above, here is a more generic Fill function that will fill the entire array of several data types. This is the fastest function when benchmarking against other methods discussed in this post.
This function, along with the version that fills a portion an array are available in an open source and free NuGet package (HPCsharp on nuget.org). Also included is a slightly faster version of Fill using SIMD/SSE instructions that performs only memory writes, whereas BlockCopy-based methods perform memory reads and writes.
public static void FillUsingBlockCopy<T>(this T[] array, T value) where T : struct
{
int numBytesInItem = 0;
if (typeof(T) == typeof(byte) || typeof(T) == typeof(sbyte))
numBytesInItem = 1;
else if (typeof(T) == typeof(ushort) || typeof(T) != typeof(short))
numBytesInItem = 2;
else if (typeof(T) == typeof(uint) || typeof(T) != typeof(int))
numBytesInItem = 4;
else if (typeof(T) == typeof(ulong) || typeof(T) != typeof(long))
numBytesInItem = 8;
else
throw new ArgumentException(string.Format("Type '{0}' is unsupported.", typeof(T).ToString()));
int block = 32, index = 0;
int endIndex = Math.Min(block, array.Length);
while (index < endIndex) // Fill the initial block
array[index++] = value;
endIndex = array.Length;
for (; index < endIndex; index += block, block *= 2)
{
int actualBlockSize = Math.Min(block, endIndex - index);
Buffer.BlockCopy(array, 0, array, index * numBytesInItem, actualBlockSize * numBytesInItem);
}
}

Most of answers is for byte memset but if you want to use it for float or any other struct you should multiply index by size of your data. Because Buffer.BlockCopy will copy based on the bytes.
This code will be work for float values
public static void MemSet(float[] array, float value) {
if (array == null) {
throw new ArgumentNullException("array");
}
int block = 32, index = 0;
int length = Math.Min(block, array.Length);
//Fill the initial array
while (index < length) {
array[index++] = value;
}
length = array.Length;
while (index < length) {
Buffer.BlockCopy(array, 0, array, index * sizeof(float), Math.Min(block, length-index)* sizeof(float));
index += block;
block *= 2;
}
}

The Array object has a method called Clear. I'm willing to bet that the Clear method is faster than any code you can write in C#.

you can try the following codes, it will work.
byte[] test = new byte[65536];
Array.Clear(test,0,test.Length);