IP.cpp

/*
 * Copyright(c) Sophist Solutions, Inc. 1990-2025.  All rights reserved
 */
#include "Stroika/Foundation/StroikaPreComp.h"
 
#include "Stroika/Foundation/IO/Network/HTTP/Headers.h"
 
#include "IP.h"
 
using namespace Stroika::Foundation;
using namespace Stroika::Foundation::Characters;
using namespace Stroika::Foundation::IO::Network;
using namespace Stroika::Foundation::IO::Network::InternetProtocol;
 
/*
 ********************************************************************************
 ***************** IO::Network::InternetProtocol::ip_checksum *******************
 ********************************************************************************
 */
uint16_t InternetProtocol::IP::ip_checksum (const void* packetStart, const void* packetEnd)
{
    const uint16_t* buffer = reinterpret_cast<const uint16_t*> (packetStart);
    ptrdiff_t       size   = reinterpret_cast<const uint8_t*> (packetEnd) - reinterpret_cast<const uint8_t*> (packetStart);
    unsigned long   cksum  = 0;
 
    // Sum all the words together, adding the final byte if size is odd
    while (size > 1) {
        cksum += *buffer++;
        size -= sizeof (uint16_t);
    }
    if (size) {
        cksum += *reinterpret_cast<const uint8_t*> (buffer);
    }
 
    // Do a little shuffling
    cksum = (cksum >> 16) + (cksum & 0xffff);
    cksum += (cksum >> 16);
 
    // Return the bitwise complement of the resulting mishmash
    return (uint16_t)(~cksum);
}