C51 COMPILER V7.06   CKSUM                                                                 07/29/2006 13:15:57 PAGE 1   


C51 COMPILER V7.06, COMPILATION OF MODULE CKSUM
OBJECT MODULE PLACED IN Cksum.OBJ
COMPILER INVOKED BY: c:\KEIL\C51\BIN\C51.exe Cksum.c DB OE

stmt level    source

   1          /*
   2          ;-------------------------------------------------------------------------
   3          ; Copyright (c) 2002 Jim Brady
   4          ; Do not use commercially without author's permission
   5          ; Last revised August 2002
   6          ; CKSUM.A51
   7          ;
   8          ; This computes the internet checksum on an 8051
   9          ;
  10          ; Call from C program: UINT cksum(UCHAR xdata * buf, UINT length);
  11          ; Where * buf is pointer to first char (must be in xdata space)
  12          ; and "length" is number of bytes (not words) to sum over
  13          ;-------------------------------------------------------------------------
  14          */
  15          #include "net.h"
  16          
  17          UINT cksum(UCHAR xdata *check,UINT length) //計(jì)算校驗(yàn)和
  18          {
  19   1              LONG sum=0;
  20   1              UINT i;
  21   1              UINT xdata *ptr; 
  22   1          ptr=(UINT xdata *)check;
  23   1              for (i=0;i<(length)/2;i++)
  24   1              {
  25   2                      sum+=*ptr++;
  26   2              }
  27   1              if (length&0x01)//表示長度為單數(shù)
  28   1              {
  29   2                      sum=sum+((*ptr)&0xff00);
  30   2              }
  31   1              sum=(sum&0xffff)+((sum>>16)&0xffff);//高16位和低16位相加
  32   1              if(sum&0xffff0000)
  33   1              {//表示有進(jìn)位
  34   2                      sum++;
  35   2              }
  36   1              return ( (UINT)((sum)&0xffff));
  37   1      //      return ( (UINT)(~((sum)&0xffff)));
  38   1      }
  39          


MODULE INFORMATION:   STATIC OVERLAYABLE
   CODE SIZE        =    202    ----
   CONSTANT SIZE    =   ----    ----
   XDATA SIZE       =   ----    ----
   PDATA SIZE       =   ----    ----
   DATA SIZE        =   ----       8
   IDATA SIZE       =   ----    ----
   BIT SIZE         =   ----    ----
END OF MODULE INFORMATION.


C51 COMPILATION COMPLETE.  0 WARNING(S),  0 ERROR(S)