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Add support for custom CRC seed and polynomials.

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This commit is contained in:
Natalia Portillo
2018-02-03 18:36:23 +00:00
parent 4f9d2fdb89
commit c06fc84348
3 changed files with 160 additions and 63 deletions
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73
DiscImageChef.Checksums/CRC32Context.cs
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@@ -41,18 +41,22 @@ namespace DiscImageChef.Checksums
/// </summary>
public class Crc32Context : IChecksum
{
const uint CRC32_POLY = 0xEDB88320;
const uint CRC32_SEED = 0xFFFFFFFF;
const uint CRC32_ISO_POLY = 0xEDB88320;
const uint CRC32_ISO_SEED = 0xFFFFFFFF;
const uint CRC32_CASTAGNOLI_POLY = 0x8F6E37A0;
const uint CRC32_CASTAGNOLI_SEED = 0xFFFFFFFF;
readonly uint finalSeed;
readonly uint[] table;
uint hashInt;
/// <summary>
/// Initializes the CRC32 table and seed
/// Initializes the CRC32 table and seed as CRC32-ISO
/// </summary>
public Crc32Context()
{
hashInt = CRC32_SEED;
hashInt = CRC32_ISO_SEED;
finalSeed = CRC32_ISO_SEED;
table = new uint[256];
for(int i = 0; i < 256; i++)
@@ -60,7 +64,29 @@ namespace DiscImageChef.Checksums
uint entry = (uint)i;
for(int j = 0; j < 8; j++)
if((entry & 1) == 1)
entry = (entry >> 1) ^ CRC32_POLY;
entry = (entry >> 1) ^ CRC32_ISO_POLY;
else
entry = entry >> 1;
table[i] = entry;
}
}
/// <summary>
/// Initializes the CRC32 table with a custom polynomial and seed
/// </summary>
public Crc32Context(uint polynomial, uint seed)
{
hashInt = seed;
finalSeed = seed;
table = new uint[256];
for(int i = 0; i < 256; i++)
{
uint entry = (uint)i;
for(int j = 0; j < 8; j++)
if((entry & 1) == 1)
entry = (entry >> 1) ^ polynomial;
else
entry = entry >> 1;
@@ -93,7 +119,7 @@ namespace DiscImageChef.Checksums
public byte[] Final()
{
BigEndianBitConverter.IsLittleEndian = BitConverter.IsLittleEndian;
return BigEndianBitConverter.GetBytes(hashInt ^ CRC32_SEED);
return BigEndianBitConverter.GetBytes(hashInt ^ finalSeed);
}
/// <summary>
@@ -104,8 +130,8 @@ namespace DiscImageChef.Checksums
StringBuilder crc32Output = new StringBuilder();
BigEndianBitConverter.IsLittleEndian = BitConverter.IsLittleEndian;
for(int i = 0; i < BigEndianBitConverter.GetBytes(hashInt ^ CRC32_SEED).Length; i++)
crc32Output.Append(BigEndianBitConverter.GetBytes(hashInt ^ CRC32_SEED)[i].ToString("x2"));
for(int i = 0; i < BigEndianBitConverter.GetBytes(hashInt ^ finalSeed).Length; i++)
crc32Output.Append(BigEndianBitConverter.GetBytes(hashInt ^ finalSeed)[i].ToString("x2"));
return crc32Output.ToString();
}
@@ -127,10 +153,19 @@ namespace DiscImageChef.Checksums
/// <param name="hash">Byte array of the hash value.</param>
public static string File(string filename, out byte[] hash)
{
FileStream fileStream = new FileStream(filename, FileMode.Open);
uint localhashInt;
return File(filename, out hash, CRC32_ISO_POLY, CRC32_ISO_SEED);
}
localhashInt = CRC32_SEED;
/// <summary>
/// Gets the hash of a file in hexadecimal and as a byte array.
/// </summary>
/// <param name="filename">File path.</param>
/// <param name="hash">Byte array of the hash value.</param>
public static string File(string filename, out byte[] hash, uint polynomial, uint seed)
{
FileStream fileStream = new FileStream(filename, FileMode.Open);
uint localhashInt = seed;
uint[] localTable = new uint[256];
for(int i = 0; i < 256; i++)
@@ -138,7 +173,7 @@ namespace DiscImageChef.Checksums
uint entry = (uint)i;
for(int j = 0; j < 8; j++)
if((entry & 1) == 1)
entry = (entry >> 1) ^ CRC32_POLY;
entry = (entry >> 1) ^ polynomial;
else
entry = entry >> 1;
@@ -146,15 +181,9 @@ namespace DiscImageChef.Checksums
}
for(int i = 0; i < fileStream.Length; i++)
{
localhashInt = (localhashInt >> 8) ^
localTable[fileStream.ReadByte() ^ (localhashInt & 0xff)];
if((localhashInt ^ CRC32_SEED) == 0xB883C628 ||
(localhashInt ^ CRC32_SEED) == 0x28C683B8)
System.Console.WriteLine("CRC found at position {0}", fileStream.Position);
}
localhashInt = (localhashInt >> 8) ^ localTable[fileStream.ReadByte() ^ (localhashInt & 0xff)];
localhashInt ^= CRC32_SEED;
localhashInt ^= seed;
BigEndianBitConverter.IsLittleEndian = BitConverter.IsLittleEndian;
hash = BigEndianBitConverter.GetBytes(localhashInt);
@@ -175,7 +204,7 @@ namespace DiscImageChef.Checksums
/// <param name="hash">Byte array of the hash value.</param>
public static string Data(byte[] data, uint len, out byte[] hash)
{
return Data(data, len, out hash, CRC32_POLY, CRC32_SEED);
return Data(data, len, out hash, CRC32_ISO_POLY, CRC32_ISO_SEED);
}
/// <summary>
@@ -208,7 +237,7 @@ namespace DiscImageChef.Checksums
for(int i = 0; i < len; i++)
localhashInt = (localhashInt >> 8) ^ localTable[data[i] ^ (localhashInt & 0xff)];
localhashInt ^= CRC32_SEED;
localhashInt ^= seed;
BigEndianBitConverter.IsLittleEndian = BitConverter.IsLittleEndian;
hash = BigEndianBitConverter.GetBytes(localhashInt);