public static unsafe ushort Substract(ushort crc1, ushort crc2, long len2)
{
crc1 = Crc16.Reflect(crc1);
crc2 = Crc16.Reflect(crc2);
/* degenerate case */
if (len2 == 0)
{
return(crc1);
}
if (len2 < 0)
throw new ArgumentException("crc.Combine length cannot be negative", "len2"); }
static unsafe Crc16()
{
for (ushort i = 0; i < table.Length; i++)
{
int crc = i;
for (int j = 0; j < GF2_DIM; j++)
{
if ((crc & (1U << (GF2_DIM - 1))) != 0)
{
crc = ((crc << 1) ^ polynomial);
}
else
{
crc <<= 1;
}
}
table[i] = (ushort)(crc & ((1 << GF2_DIM) - 1));
}
combineTable[0, 0] = Crc16.Reflect(polynomial);
substractTable[0, GF2_DIM - 1] = reversePolynomial;
for (int n = 1; n < GF2_DIM; n++)
{
combineTable[0, n] = (ushort)(1 << (n - 1));
substractTable[0, n - 1] = (ushort)(1 << n);
}
fixed(ushort *ct = &combineTable[0, 0], st = &substractTable[0, 0])
{
//for (int i = 0; i < GF2_DIM; i++)
// st[32 + i] = ct[i];
//invert_binary_matrix(st + 32, st, GF2_DIM);
for (int i = 1; i < GF2_DIM; i++)
{
gf2_matrix_square(ct + i * GF2_DIM, ct + (i - 1) * GF2_DIM);
gf2_matrix_square(st + i * GF2_DIM, st + (i - 1) * GF2_DIM);
}
}
}
public static unsafe ushort Combine(ushort crc1, ushort crc2, long len2)
{
crc1 = Crc16.Reflect(crc1);
crc2 = Crc16.Reflect(crc2);
/* degenerate case */
if (len2 == 0)
{
return(crc1);
}
if (crc1 == 0)
{
return(crc2);
}
if (len2 < 0)
{
throw new ArgumentException("crc.Combine length cannot be negative", "len2");
fixed(ushort *ct = &combineTable[0, 0])
{
int n = 3;
do
{
/* apply zeros operator for this bit of len2 */
if ((len2 & 1) != 0)
{
crc1 = gf2_matrix_times(ct + GF2_DIM * n, crc1);
}
len2 >>= 1;
n = (n + 1) & (GF2_DIM - 1);
/* if no more bits set, then done */
} while (len2 != 0);
}
/* return combined crc */
crc1 ^= crc2;
crc1 = Crc16.Reflect(crc1);
return(crc1);
}
