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namespace com.clusterrr.Famicom.Containers
{
public static class Crc32Calculator
{
static uint[] table = new uint[256];
static Crc32Calculator()
{
// Calculate table
uint poly = 0xedb88320;
uint temp;
for (uint i = 0; i < table.Length; ++i)
{
temp = i;
for (int j = 8; j > 0; --j)
{
if ((temp & 1) == 1)
{
temp = (uint)((temp >> 1) ^ poly);
}
else
{
temp >>= 1;
}
}
table[i] = temp;
}
}
/// <summary>
/// Calculate CRC32 checksum
/// </summary>
/// <param name="data">Input data</param>
/// <param name="offset">Data offset</param>
/// <param name="length">Length</param>
/// <returns></returns>
public static uint CalculateCRC32(byte[] data, int offset, int length)
{
// Calculate CRC32
uint crc = 0xffffffff;
for (int i = offset; length > 0; i++, length--)
{
byte index = (byte)(((crc) & 0xff) ^ data[i]);
crc = (crc >> 8) ^ table[index];
}
return ~crc;
}
/// <summary>
/// Calculate CRC32 checksum
/// </summary>
/// <param name="data">Input date</param>
/// <returns></returns>
public static uint CalculateCRC32(byte[] data)
=> CalculateCRC32(data, 0, data.Length);
}
}
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