mips_sys

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#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;
}
 
 
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