/// <summary> tamir:
/// Computes the one's sum on a byte array.
/// Based TCP/IP Illustrated Vol. 2(1995) by Gary R. Wright and W. Richard
/// Stevens. Page 236. And on http://www.cs.utk.edu/~cs594np/unp/checksum.html
/// </summary>
protected internal virtual int _OnesSum(byte[] bytes, int start, int len)
{
int sum = 0; /* assume 32 bit long, 16 bit short */
int i = start;
len = start + len;
while (i < len - 1)
{
sum += ArrayHelper.extractInteger(bytes, i, 2);
//if ((sum & unchecked((int)0x80000000)) != 0)
if ((sum & 0x80000000) != 0)
{
/* if high order bit set, fold */
sum = (sum & 0xFFFF) + (sum >> 16);
}
i += 2;
}
if (i < len)
{
/* take care of left over byte */
sum += ArrayHelper.extractInteger(bytes, start, 2);
}
while (sum >> 16 != 0)
{
sum = (sum & 0xFFFF) + (sum >> 16);
}
return(sum & 0xFFFF);
}
/// <summary> Fetch the header checksum.</summary>
public virtual int GetTransportLayerChecksum(int pos)
{
return(ArrayHelper.extractInteger(_bytes, pos, 2));
}