#include "inet.h"

uint16_t ntohs(uint16_t val)
{
    return val<<8|val>>8;
}
uint16_t htons(uint16_t val)
{
    return val<<8|val>>8;
}

uint16_t checksum(void *addr, int count)
{
    /* Compute Internet Checksum for "count" bytes
     *         beginning at location "addr".
     * Taken from https://tools.ietf.org/html/rfc1071
     */

    register uint32_t sum = 0;
    uint16_t * ptr = addr;

    while( count > 1 )  {
        /*  This is the inner loop */
        sum += ntohs(* ptr++);
        count -= 2;
    }

    /*  Add left-over byte, if any */
    if( count > 0 )
        sum += * (uint8_t *) ptr;

    /*  Fold 32-bit sum to 16 bits */
    while (sum>>16)
        sum = (sum & 0xffff) + (sum >> 16);

    return ~sum;
}