// Check coefficient c is a valid element in ECField field.
private static void CheckValidity(ECField field, System.Numerics.BigInteger c, String cName)
{
// can only perform check if field is ECFieldFp or ECFieldF2m.
if (field is ECFieldFp)
{
System.Numerics.BigInteger p = ((ECFieldFp)field).P;
if (p.CompareTo(c) != 1)
{
throw new IllegalArgumentException(cName + " is too large");
}
else if (c.signum() < 0)
{
throw new IllegalArgumentException(cName + " is negative");
}
}
else if (field is ECFieldF2m)
{
int m = ((ECFieldF2m)field).M;
if (c.bitLength() > m)
{
throw new IllegalArgumentException(cName + " is too large");
}
}
}