/// <summary>
/// Initializes the CRC-16 calculations.
/// </summary>
public override void Initialize()
{
if (this.definition.ReverseDataBytes)
{
this.remainder = HackersDelight.Reverse(this.definition.Initializer);
}
else
{
this.remainder = this.definition.Initializer;
}
}
/// <summary>
/// Generates a lookup table for a CRC-16 algorithm definition. Both <see cref="Definition.TruncatedPolynomial"/> and <see cref="Definition.ReverseDataBytes"/> are used in the calculations.
/// </summary>
/// <param name="definition">The CRC-16 algorithm definition. May not be <c>null</c>.</param>
/// <returns>The lookup table.</returns>
public static ushort[] GenerateLookupTable(Definition definition)
{
Contract.Requires(definition != null);
Contract.Ensures(Contract.Result <ushort[]>() != null);
Contract.Ensures(Contract.Result <ushort[]>().Length == 256);
unchecked
{
ushort[] ret = new ushort[256];
byte dividend = 0;
do
{
ushort remainder = 0;
for (byte mask = 0x80; mask != 0; mask >>= 1)
{
if ((dividend & mask) != 0)
{
remainder ^= 0x8000;
}
if ((remainder & 0x8000) != 0)
{
remainder <<= 1;
remainder ^= definition.TruncatedPolynomial;
}
else
{
remainder <<= 1;
}
}
if (definition.ReverseDataBytes)
{
var index = HackersDelight.Reverse(dividend);
Contract.Assume(index >= 0);
Contract.Assume(index <= 255);
ret[index] = HackersDelight.Reverse(remainder);
}
else
{
ret[dividend] = remainder;
}
++dividend;
}while (dividend != 0);
return(ret);
}
}