#!/usr/bin/env python
# -*- coding: utf-8 -*-
import struct
import sysdef ip_cksum(s):a = 0b = 0#  偶数序号的  unsigned char 互相累加for i in xrange(0, len(s), 2):a += struct.unpack('B', s[i])[0]# 奇数序号的 unsigned char 互相累加for i in xrange(1, len(s), 2):b += struct.unpack('B', s[i])[0]# 缩小值为 unsigned charwhile a > 256 or b > 256:b += a/256 # a 超过 byte 的部分进位给 ba = a%256a += b/256 # b 超过 byte 的部分进位给 ab = b%256# 取反a = ~a & 0xffb = ~b & 0xff# 校验和作为字符串v = chr(a) + chr(b)# 校验和作为 unsigned shortv = struct.unpack('H', v)[0]return vif __name__ == '__main__':for i in sys.argv[1:]:print ip_cksum(i)

View Code

 1 unsigned short checksum1(const char *buf, unsigned size)
 2 {
 3     unsigned sum = 0;
 4     int i;
 5
 6     /* Accumulate checksum */
 7     for (i = 0; i < size - 1; i += 2)
 8     {
 9         unsigned short word16 = *(unsigned short *) &buf[i];
10         sum += word16;
11     }
12
13     /* Handle odd-sized case */
14     if (size & 1)
15     {
16         unsigned short word16 = (unsigned char) buf[i];
17         sum += word16;
18     }
19
20     /* Fold to get the ones-complement result */
21     while (sum >> 16) sum = (sum & 0xFFFF)+(sum >> 16);
22
23     /* Invert to get the negative in ones-complement arithmetic */
24     return ~sum;
25 }

 1 try:
 2     import dnet
 3     def in_cksum_add(s, buf):
 4         return dnet.ip_cksum_add(buf, s)
 5     def in_cksum_done(s):
 6         return socket.ntohs(dnet.ip_cksum_carry(s))
 7 except ImportError:
 8     import array
 9     def in_cksum_add(s, buf):
10         n = len(buf)
11         cnt = (n / 2) * 2
12         a = array.array('H', buf[:cnt])
13         if cnt != n:
14             a.append(struct.unpack('H', buf[-1] + '\x00')[0])
15         return s + sum(a)
16     def in_cksum_done(s):
17         s = (s >> 16) + (s & 0xffff)
18         s += (s >> 16)
19         return socket.ntohs(~s & 0xffff)

  1 /*
  2  * Checksum routine for Internet Protocol family headers (Portable Version).
  3  *
  4  * This routine is very heavily used in the network
  5  * code and should be modified for each CPU to be as fast as possible.
  6  */
  7
  8 #define ADDCARRY(x)  {if ((x) > 65535) (x) -= 65535;}
  9 #define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
 10
 11 int
 12 in_cksum(const vec_t *vec, int veclen)
 13 {
 14     register const guint16 *w;
 15     register int sum = 0;
 16     register int mlen = 0;
 17     int byte_swapped = 0;
 18
 19     union {
 20         guint8    c[2];
 21         guint16    s;
 22     } s_util;
 23     union {
 24         guint16 s[2];
 25         guint32    l;
 26     } l_util;
 27
 28     for (; veclen != 0; vec++, veclen--) {
 29         if (vec->len == 0)
 30             continue;
 31         w = (const guint16 *)(const void *)vec->ptr;
 32         if (mlen == -1) {
 33             /*
 34              * The first byte of this chunk is the continuation
 35              * of a word spanning between this chunk and the
 36              * last chunk.
 37              *
 38              * s_util.c[0] is already saved when scanning previous
 39              * chunk.
 40              */
 41             s_util.c[1] = *(const guint8 *)w;
 42             sum += s_util.s;
 43             w = (const guint16 *)(const void *)((const guint8 *)w + 1);
 44             mlen = vec->len - 1;
 45         } else
 46             mlen = vec->len;
 47         /*
 48          * Force to even boundary.
 49          */
 50         if ((1 & (unsigned long) w) && (mlen > 0)) {
 51             REDUCE;
 52             sum <<= 8;
 53             s_util.c[0] = *(const guint8 *)w;
 54             w = (const guint16 *)(const void *)((const guint8 *)w + 1);
 55             mlen--;
 56             byte_swapped = 1;
 57         }
 58         /*
 59          * Unroll the loop to make overhead from
 60          * branches &c small.
 61          */
 62         while ((mlen -= 32) >= 0) {
 63             sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
 64             sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
 65             sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
 66             sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
 67             w += 16;
 68         }
 69         mlen += 32;
 70         while ((mlen -= 8) >= 0) {
 71             sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
 72             w += 4;
 73         }
 74         mlen += 8;
 75         if (mlen == 0 && byte_swapped == 0)
 76             continue;
 77         REDUCE;
 78         while ((mlen -= 2) >= 0) {
 79             sum += *w++;
 80         }
 81         if (byte_swapped) {
 82             REDUCE;
 83             sum <<= 8;
 84             byte_swapped = 0;
 85             if (mlen == -1) {
 86                 s_util.c[1] = *(const guint8 *)w;
 87                 sum += s_util.s;
 88                 mlen = 0;
 89             } else
 90                 mlen = -1;
 91         } else if (mlen == -1)
 92             s_util.c[0] = *(const guint8 *)w;
 93     }
 94     if (mlen == -1) {
 95         /* The last mbuf has odd # of bytes. Follow the
 96            standard (the odd byte may be shifted left by 8 bits
 97            or not as determined by endian-ness of the machine) */
 98         s_util.c[1] = 0;
 99         sum += s_util.s;
100     }
101     REDUCE;
102     return (~sum & 0xffff);
103 }