private Crc32(Crc32Formula formula, uint[] polynomialTable, uint initValue, uint xorOut)
{
_polynomialTable = polynomialTable ?? throw new ArgumentNullException(nameof(polynomialTable));
_formula = formula;
_initValue = initValue;
_xorOut = xorOut;
}
private static uint[] InitializeTable(Crc32Formula formula, uint polynomial)
{
if (formula == Crc32Formula.Normal && polynomial == DefaultPolynomial)
{
return(_defaultCrc32Table);
}
if (formula == Crc32Formula.Reflected && polynomial == DefaultReflectedPolynomial)
{
return(_defaultReflectedCrc32Table);
}
var polynomialTable = new uint[256];
for (uint i = 0; i < 256; i++)
{
uint entry;
if (formula == Crc32Formula.Normal)
{
entry = i << 24;
for (var j = 0; j < 8; j++)
{
if ((entry & 0x80000000) != 0)
{
entry = (entry << 1) ^ polynomial;
}
else
{
entry <<= 1;
}
}
}
else
{
entry = i;
for (var j = 0; j < 8; j++)
{
if ((entry & 1) == 1)
{
entry = (entry >> 1) ^ polynomial;
}
else
{
entry >>= 1;
}
}
}
polynomialTable[i] = entry;
}
return(polynomialTable);
}
public static Crc32 Create(Crc32Formula formula, uint polynomial)
{
var table = InitializeTable(formula, polynomial);
return(new Crc32(formula, table));
}
public static Crc32 Create(Crc32Formula formula)
{
return(new Crc32(formula, formula == Crc32Formula.Normal ?
_defaultCrc32Table :
_defaultReflectedCrc32Table));
}
private Crc32(Crc32Formula formula, uint[] polynomialTable)
{
_polynomialTable = polynomialTable ?? throw new ArgumentNullException(nameof(polynomialTable));
_formula = formula;
}
public static Crc32 Create(Crc32Formula formula, uint polynomial, uint initValue = 0xFFFFFFFF, uint xorOut = 0xFFFFFFFF)
{
var table = InitializeTable(formula, polynomial);
return(new Crc32(formula, table, initValue, xorOut));
}