Novacoin/VarInt.cs

   1 \feffusing System;
   2 using System.Collections.Generic;
   3 using System.Linq;
   4 using System.Text;
   5 using System.Threading.Tasks;
   6
   7 namespace Novacoin
   8 {
   9     public class VarInt
  10     {
  11         /// <summary>
  12         /// Encodes unsigned integer value into compact representation.
  13         ///
  14         /// See https://bitcoin.org/en/developer-reference#compactsize-unsigned-integers for additional information.
  15         /// </summary>
  16         /// <param name="n">Unsigned integer value</param>
  17         /// <returns>Byte sequence</returns>
  18         public static IList<byte> EncodeVarInt(ulong n)
  19         {
  20             List<byte> resultBytes = new List<byte>();
  21
  22             if (n <= 0xfc)
  23             {
  24                 // Values up to 0xfc are stored directly without any prefix
  25                 resultBytes.Add((byte)n);
  26             }
  27             else
  28             {
  29                 byte prefix;
  30                 byte[] valueBytes;
  31
  32                 if (n <= ushort.MaxValue)
  33                 {
  34                     // ushort flag
  35                     prefix = 0xfd;
  36                     valueBytes = BitConverter.GetBytes((ushort)n);
  37                 }
  38                 else if (n <= uint.MaxValue)
  39                 {
  40                     // uint flag
  41                     prefix = 0xfe;
  42                     valueBytes = BitConverter.GetBytes((uint)n);
  43                 }
  44                 else
  45                 {
  46                     // ulong flag
  47                     prefix = 0xff;
  48                     valueBytes = BitConverter.GetBytes(n);
  49                 }
  50
  51                 resultBytes.Add(prefix);
  52                 resultBytes.AddRange(valueBytes);
  53             }
  54
  55             return resultBytes;
  56         }
  57
  58         /// <summary>
  59         /// Encodes integer value into compact representation.
  60         ///
  61         /// See https://bitcoin.org/en/developer-reference#compactsize-unsigned-integers for additional information.
  62         /// </summary>
  63         /// <param name="n">Integer value</param>
  64         /// <returns>Byte sequence</returns>
  65         public static IList<byte> EncodeVarInt(long n)
  66         {
  67             return EncodeVarInt((ulong)n);
  68         }
  69
  70         /// <summary>
  71         /// Decodes integer value from compact representation
  72         ///
  73         /// See https://bitcoin.org/en/developer-reference#compactsize-unsigned-integers for additional information.
  74         /// </summary>
  75         /// <param name="bytes">Byte sequence</param>
  76         /// <returns>Integer value</returns>
  77         public static ulong DecodeVarInt(IList<byte> bytes)
  78         {
  79             byte prefix = bytes[0];
  80
  81             bytes.RemoveAt(0); // Remove prefix
  82
  83             byte[] bytesArray = bytes.ToArray();
  84
  85             switch (prefix)
  86             {
  87                 case 0xfd: // ushort flag
  88                     return BitConverter.ToUInt16(bytesArray, 0);
  89                 case 0xfe: // uint flag
  90                     return BitConverter.ToUInt32(bytesArray, 0);
  91                 case 0xff: // ulong flag
  92                     return BitConverter.ToUInt64(bytesArray, 0);
  93                 default:
  94                     return prefix;
  95             }
  96         }
  97     }
  98 }