OBS Framework: Checksum.cpp Source File

00001 // 00002 // Copyright 2004 P&P Software GmbH - All Rights Reserved 00003 // 00004 // Checksum.cpp 00005 // 00006 // Version 1.0 00007 // Date 13.01.04 00008 // Author A. Pasetti (P&P Software) 00009 00010 #include "../GeneralInclude/CompilerSwitches.h" 00011 #include "../GeneralInclude/DebugSupport.h" 00012 #include "../GeneralInclude/Constants.h" 00013 #include "../Utilities/Checksum.h" 00014 00015 unsigned short doChecksum(unsigned char* item, unsigned int n) { 00016 assert( item!=pNULL ); 00017 assert( n>0 ); 00018 00019 C0 = 0; 00020 C1 = 0; 00021 00022 for (unsigned int i=0; i<n; i++) { 00023 C0 = C0 + (int)item[i]; 00024 C1 = C1 + C0; 00025 } 00026 00027 CK1 = (unsigned char)(255-((C0+C1)%255)); 00028 CK2 = (unsigned char)(C1%255); 00029 00030 if (CK1==0) 00031 CK1=255; 00032 00033 if (CK2==0) 00034 CK2=255; 00035 00036 return (CK1*256+CK2); 00037 } 00038 00039 bool verifyChecksum(unsigned char* item, unsigned int n, unsigned short checksum) { 00040 assert( item!=pNULL ); 00041 assert( n>0 ); 00042 00043 CK1 = (unsigned char)(checksum/256); 00044 CK2 = (unsigned char)(checksum%256); 00045 00046 if ( ((CK1==0)&&(CK2!=0)) || ((CK1!=0)&&(CK2==0)) ) 00047 return false; 00048 00049 C0 = 0; 00050 C1 = 0; 00051 00052 for (unsigned int i=0; i<n; i++) { 00053 C0 = C0 + (unsigned short)item[i]; 00054 C1 = C1 + C0; 00055 } 00056 00057 C0 = C0 + CK1; 00058 C1 = C1 + C0; 00059 00060 C0 = C0 + CK2; 00061 C1 = C1 + C0; 00062 00063 if ( ( (C0%255)==0) && ( (C1%255)==0) ) 00064 return true; 00065 else 00066 return false; 00067 }