10. december 2002 - 10:01
#3
Du har ret!!! - stupid me, det burde jeg have set...
Men chries, så forholder det sig sådan, at jeg har haft præcis det samme problem med en anden CRC16! - jeg har nu kigget koden igennem efter steder, hvor jeg burde initialisere min variable, men kan ikke se fejlen! - kan du evt. hjælpe?
Koden ser således ud:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "headere.h"
int getChecksum(struct standardheader* pakke){
char up,low;
char result[2];
int tempchecksum=pakke->checksum; //gemmer den gamle checksum
char buf[65000];
pakke->checksum=0;
memcpy(buf, pakke, sizeof(struct standardheader));
memcpy(buf+sizeof(struct standardheader), pakke->payload, pakke->payloadlaengde);
beregnChecksum(buf,sizeof(struct standardheader)+pakke->payloadlaengde, &up, &low);
result[0]=low;
result[1]=up;
pakke->checksum=tempchecksum;
return *((int*)result);
}
//*************************************************************
//Konstruerer en CRC lookup tabel
//*************************************************************
int crctab[] = /* CRC lookup table */
{
0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,
0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,
0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,
0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,
0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,
0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040
};
//*************************************************************************
int beregnChecksum(char *buf, int len ,char *crc1, char *crc2)
// Udregner CRC16 på en given buffer
// Input :
// *buf : Pointer til en char buffer som der skal udregnes cheksum på
// len : Antal chars i buf
// Output:
// crc1 : Her retuneres mest betydende byte af den udregnede crc
// crc2 : Her retuneres mindst betydende byte af den udregnede crc
//*************************************************************************
{
int i,crc;
for (i=0; i<len; i++)
crc = ((crc >> 8) & 0xff) ^ crctab[(crc ^ *buf++) & 0xff];
//opdel 16 bit crc i 2 bytes
*crc1 = crc / 256;
*crc2 = crc % 256;
return 0;
}
/*kun til test
**************
*int main (void){
* char buffer[100];
* int resultat,i;
* struct standardheader header;
* header.version=1;
* header.pakketype=1;
* header.kvitteret=1;
* header.krypteret=2;
* header.dataid=1;
* header.checksum=0;
* header.payloadlaengde=10;
* header.fragmentnummer=1;
* header.timestamp=1000;
* header.totalstoerrelse=500;
* header.payload=malloc(10);
* strcpy(header.payload,"hjghygtdf");
* memcpy(buffer,(char*)&header,sizeof(struct standardheader));
* memcpy(buffer+sizeof(struct standardheader),header.payload,header.payloadlaengde);
* resultat=getChecksum((struct standardheader*)buffer);
* printf("resultat: %d \n", resultat);
*return 0;
* }
*/
Ellers tusind tak for hjælpen....
