C int to byte

Question

I need to convert an int to a byte   one way of doing it is to use BitConverter GetBytes    But im unsure if that matches the following specification       An XDR signed integer is a 32-bit datum that encodes an integer in      the range  -2147483648 2147483647    The integer is represented in      two s complement notation   The most and least significant bytes are      0 and 3  respectively   Integers are declared as follows    Source  RFC1014 3 2  How could i do a int to byte transformation that would satisfy the above specification

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The other way is to use BinaryPrimitives like so  byte   intBytes   BitConverter GetBytes 123    int actual   BinaryPrimitives ReadInt32LittleEndian intBytes

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Why all this code in the samples above     A struct with explicit layout acts both ways and has no performance hit   Update  Since there s a question on how to deal with endianness I added an interface that illustrates how to abstract that  Another implementing struct can deal with the opposite case  public interface IIntToByte       Int32 Int   get  set        byte B0   get        byte B1   get        byte B2   get        byte B3   get        StructLayout LayoutKind Explicit   public struct IntToByteLE   UserQuery IIntToByte        FieldOffset 0       public Int32 IntVal        FieldOffset 0       public byte b0       FieldOffset 1       public byte b1       FieldOffset 2       public byte b2       FieldOffset 3       public byte b3       public Int32 Int           get  return IntVal            set  IntVal   value              public byte B0   gt  b0      public byte B1   gt  b1      public byte B2   gt  b2      public byte B3   gt  b3

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When I look at this description  I have a feeling  that this xdr integer is just a big-endian  standard  integer  but it s expressed in the most obfuscated way  Two s complement notation is better know as U2  and it s what we are using on today s processors  The byte order indicates that it s a big-endian notation  So  answering your question  you should inverse elements in your array  0  lt --  3  1  lt -- 2   as they are encoded in little-endian  Just to make sure  you should first check BitConverter IsLittleEndian to see on what machine you are running

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If you want more general information about various methods of representing numbers including Two s Complement have a look at   Two s Complement and Signed Number Representation on Wikipedia

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Here s another way to do it  as we all know 1x byte   8x bits and also  a  regular  integer  int32  contains 32 bits  4 bytes   We can use the    operator to shift bits right     operator does not change value    int intValue   566   byte   bytes   new byte 4    bytes 0     byte  intValue  gt  gt  24   bytes 1     byte  intValue  gt  gt  16   bytes 2     byte  intValue  gt  gt  8   bytes 3     byte intValue   Console WriteLine   0  breaks down to    1   2   3   4        intValue  bytes 0   bytes 1   bytes 2   bytes 3

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byte   Take Byte Arr From Int Int64 Source Num       Int64 Int64 Num   Source Num     byte Byte Num     byte   Byte Arr   new byte 8      for  int i   0  i  lt  8  i               if  Source Num  gt  255                   Int64 Num   Source Num   256           Byte Num    byte  Source Num - Int64 Num   256                 else                  Byte Num    byte Int64 Num           Int64 Num   0                Byte Arr i    Byte Num        Source Num   Int64 Num          return  Byte Arr

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The RFC is just trying to say that a signed integer is a normal 4-byte integer with bytes ordered in a big-endian way   Now  you are most probably working on a little-endian machine and BitConverter GetBytes   will give you the byte   reversed  So you could try   int intValue  byte   intBytes   BitConverter GetBytes intValue   Array Reverse intBytes   byte   result   intBytes    For the code to be most portable  however  you can do it like this   int intValue  byte   intBytes   BitConverter GetBytes intValue   if  BitConverter IsLittleEndian      Array Reverse intBytes   byte   result   intBytes

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using static System Console   namespace IntToBits       class Program               static void Main                         while  true                                string s   Console ReadLine                    Clear                    uint i                  bool b   UInt32 TryParse s  out i                   if  b  IntPrinter i                                    static void IntPrinter uint i                        int   iarr   new int  32               Write                   for  int j   0  j  lt  32  j                                  uint tmp   i  amp   uint Math Pow 2  j                    iarr j     int  tmp  gt  gt  j                             for  int j   32  j  gt  0  j--                                if j 8  0  amp  amp  j    32 Write                       if j 4  0  amp  amp  j 8   0  Write                       Write iarr j-1                              WriteLine

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BitConverter GetBytes int  almost does what you want  except the endianness is wrong   You can use the IPAddress HostToNetwork method to swap the bytes within the the integer value before using BitConverter GetBytes or use Jon Skeet s EndianBitConverter class  Both methods do the right thing tm  regarding portability   int value  byte   bytes   BitConverter GetBytes IPAddress HostToNetworkOrder value

[c#] C# int to byte[]

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