checksum.c

   1
   2 /*
   3  * libjio - A library for Journaled I/O
   4  * Alberto Bertogli (albertogli@telpin.com.ar)
   5  *
   6  * Checksum functions
   7  * Based on RFC 1071, "Computing the Internet Checksum"
   8  */
   9
  10 #include <stddef.h>
  11 #include <stdint.h>
  12 #include <sys/mman.h>
  13 #include "common.h"
  14
  15
  16 int checksum(int fd, size_t len, uint32_t *csum)
  17 {
  18         uint8_t *map;
  19
  20         map = (uint8_t *) mmap(NULL, len, PROT_READ, MAP_SHARED, fd, 0);
  21         if (map == MAP_FAILED)
  22                 return 0;
  23
  24         *csum = checksum_map(map, len);
  25
  26         munmap(map, len);
  27         return 1;
  28 }
  29
  30 uint32_t checksum_map(uint8_t *map, size_t count)
  31 {
  32         uint32_t sum = 0;
  33
  34         while( count > 1 )  {
  35                 sum += * (uint16_t *) map++;
  36                 count -= 2;
  37         }
  38
  39         if( count > 0 )
  40                 sum += * (uint8_t *) map;
  41
  42         while (sum >> 16)
  43                 sum = (sum & 0xffff) + (sum >> 16);
  44
  45         return ~sum;
  46 }
  47