fw/checksum.c (c2b0401) - mips_sys · BlinkenArea

checksum.c

/* MIPS I system
 * Copyright 2011-2012 Stefan Schuermans <stefan@schuermans.info>
 * Copyleft GNU public license V2 or later
 *          http://www.gnu.org/copyleft/gpl.html
 */

#include "checksum.h"
#include "macros.h"
#include "nethelp.h"

/**
 * @brief generate an IP style checksum
 * @param[in] ptr pointer to data
 * @param[in] sz size of data
 * @param[in] pseudo1 additional value to include - set to 0 if not needed
 * @param[in] preude2 additional value to include - set to 0 if not needed
 *
 * can also be used to check a checksum (returns 0 if correct)
 */
unsigned short checksum(void *ptr, unsigned int sz,
                        unsigned short pseudo1, unsigned short pseudo2)
{
  unsigned int sum;
  unsigned short *data;

// sum up data of pseudo header
  sum = pseudo1;
  sum += pseudo2;

// add full 16 bit words in header
  for (data = ptr; sz >= 2; data++, sz -= 2)
    sum += ntohs(*data);

// add last byte
  if (sz >= 1)
    sum += *(unsigned char *)data << 8;

// convert sum to one's complement sum
  //   add carries (bits 31..16) to sum (bits 15..0)
  sum = (sum & 0x0000FFFF) + (sum >> 16);
  //   still a carry possible (from last addition)
  sum = (sum & 0x0000FFFF) + (sum >> 16);

// return complement of one's complement sum
  return ~(unsigned short)sum;
}

mips_sys

added file headers