text: /**
   * @file
   * Functions common to all TCP/IPv6 modules, such as the Internet checksum and the
   * byte order functions.
   *
   */
  
  /*
   * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
   * All rights reserved. 
   * 
   * Redistribution and use in source and binary forms, with or without modification, 
   * are permitted provided that the following conditions are met:
   *
   * 1. Redistributions of source code must retain the above copyright notice,
   *    this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright notice,
   *    this list of conditions and the following disclaimer in the documentation
   *    and/or other materials provided with the distribution.
   * 3. The name of the author may not be used to endorse or promote products
   *    derived from this software without specific prior written permission. 
   *
   * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED 
   * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 
   * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT 
   * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 
   * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT 
   * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 
   * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 
   * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING 
   * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY 
   * OF SUCH DAMAGE.
   *
   * This file is part of the lwIP TCP/IP stack.
   * 
   * Author: Adam Dunkels <adam@sics.se>
   *
   */
   /**
   * Support and FAQ: visit <a href="http://www.atmel.com/design-support/">Atmel Support</a>
   */
  
  #include "lwip/opt.h"
  
  #include "lwip/def.h"
  #include "lwip/inet.h"
  
  /* chksum:
   *
   * Sums up all 16 bit words in a memory portion. Also includes any odd byte.
   * This function is used by the other checksum functions.
   *
   * For now, this is not optimized. Must be optimized for the particular processor
   * arcitecture on which it is to run. Preferebly coded in assembler.
   */
  
  static u32_t
  chksum(void *dataptr, u16_t len)
  {
    u16_t *sdataptr = dataptr;
    u32_t acc;
    
    
    for(acc = 0; len > 1; len -= 2) {
      acc += *sdataptr++;
    }
  
    /* add up any odd byte */
    if (len == 1) {
      acc += htons((u16_t)(*(u8_t *)dataptr) << 8);
    }
  
    return acc;
  
  }
  
  /* inet_chksum_pseudo:
   *
   * Calculates the pseudo Internet checksum used by TCP and UDP for a pbuf chain.
   */
  
  u16_t
  inet_chksum_pseudo(struct pbuf *p,
         struct ip_addr *src, struct ip_addr *dest,
         u8_t proto, u32_t proto_len)
  {
    u32_t acc;
    struct pbuf *q;
    u8_t swapped, i;
  
    acc = 0;
    swapped = 0;
    for(q = p; q != NULL; q = q->next) {    
      acc += chksum(q->payload, q->len);
      while (acc >> 16) {
        acc = (acc & 0xffff) + (acc >> 16);
      }
      if (q->len % 2 != 0) {
        swapped = 1 - swapped;
        acc = ((acc & 0xff) << 8) | ((acc & 0xff00) >> 8);
      }
    }
  
    if (swapped) {
      acc = ((acc & 0xff) << 8) | ((acc & 0xff00) >> 8);
    }
    
    for(i = 0; i < 8; i++) {
      acc += ((u16_t *)src->addr)[i] & 0xffff;
      acc += ((u16_t *)dest->addr)[i] & 0xffff;
      while (acc >> 16) {
        acc = (acc & 0xffff) + (acc >> 16);
      }
    }
    acc += (u16_t)htons((u16_t)proto);
    acc += ((u16_t *)&proto_len)[0] & 0xffff;
    acc += ((u16_t *)&proto_len)[1] & 0xffff;
  
    while (acc >> 16) {
      acc = (acc & 0xffff) + (acc >> 16);
    }
    return ~(acc & 0xffff);
  }
  
  /* inet_chksum:
   *
   * Calculates the Internet checksum over a portion of memory. Used primarely for IP
   * and ICMP.
   */
  
  u16_t
  inet_chksum(void *dataptr, u16_t len)
  {
    u32_t acc, sum;
  
    acc = chksum(dataptr, len);
    sum = (acc & 0xffff) + (acc >> 16);
    sum += (sum >> 16);
    return ~(sum & 0xffff);
  }
  
  u16_t
  inet_chksum_pbuf(struct pbuf *p)
  {
    u32_t acc;
    struct pbuf *q;
    u8_t swapped;
    
    acc = 0;
    swapped = 0;
    for(q = p; q != NULL; q = q->next) {
      acc += chksum(q->payload, q->len);
      while (acc >> 16) {
        acc = (acc & 0xffff) + (acc >> 16);
      }    
      if (q->len % 2 != 0) {
        swapped = 1 - swapped;
        acc = (acc & 0xff << 8) | (acc & 0xff00 >> 8);
      }
    }
   
    if (swapped) {
      acc = ((acc & 0xff) << 8) | ((acc & 0xff00) >> 8);
    }
    return ~(acc & 0xffff);
  }
  