vcs.maemo.org Git - physicsfs/blob - lzma/CS/7zip/Common/CRC.cs

   1 // Common/CRC.cs
   2
   3 namespace SevenZip
   4 {
   5         class CRC
   6         {
   7                 public static readonly uint[] Table;
   8
   9                 static CRC()
  10                 {
  11                         Table = new uint[256];
  12                         const uint kPoly = 0xEDB88320;
  13                         for (uint i = 0; i < 256; i++)
  14                         {
  15                                 uint r = i;
  16                                 for (int j = 0; j < 8; j++)
  17                                         if ((r & 1) != 0)
  18                                                 r = (r >> 1) ^ kPoly;
  19                                         else
  20                                                 r >>= 1;
  21                                 Table[i] = r;
  22                         }
  23                 }
  24
  25                 uint _value = 0xFFFFFFFF;
  26
  27                 public void Init() { _value = 0xFFFFFFFF; }
  28
  29                 public void UpdateByte(byte b)
  30                 {
  31                         _value = Table[(((byte)(_value)) ^ b)] ^ (_value >> 8);
  32                 }
  33
  34                 public void Update(byte[] data, uint offset, uint size)
  35                 {
  36                         for (uint i = 0; i < size; i++)
  37                                 _value = Table[(((byte)(_value)) ^ data[offset + i])] ^ (_value >> 8);
  38                 }
  39
  40                 public uint GetDigest() { return _value ^ 0xFFFFFFFF; }
  41
  42                 static uint CalculateDigest(byte[] data, uint offset, uint size)
  43                 {
  44                         CRC crc = new CRC();
  45                         // crc.Init();
  46                         crc.Update(data, offset, size);
  47                         return crc.GetDigest();
  48                 }
  49
  50                 static bool VerifyDigest(uint digest, byte[] data, uint offset, uint size)
  51                 {
  52                         return (CalculateDigest(data, offset, size) == digest);
  53                 }
  54         }
  55 }