CodeSearch Entry

Title : Checksum (c++)

User : fst

A checksum is a value which is computed which allows you to check the validity of something. Typically, checksums are used in data transmission contexts to detect if the data has been transmitted successfully.

Checksum.h

class checksum {
public:
checksum() { clear(); }
void clear() { sum = 0; r = 55665; c1 = 52845; c2 = 22719;}
void add(DWORD w);
void add(BOOL w) { add((DWORD)w); }
void add(UINT w) { add((DWORD)w); }
void add(WORD w);
void add(const CString & s);
void add(LPBYTE b, UINT length);
void add(BYTE b);
DWORD get() { return sum; }
protected:
WORD r;
WORD c1;
WORD c2;
DWORD sum;
};

Checksum.cpp

#include "stdafx.h"

#include "Checksum.h"

/****************************************************************************
* checksum::add
* Inputs:
* DWORD d: word to add
* Result: void
*
* Effect:
* Adds the bytes of the DWORD to the checksum
****************************************************************************/

void checksum::add(DWORD value)
{
union { DWORD value; BYTE bytes[4]; } data;
data.value = value;
for(UINT i = 0; i < sizeof(data.bytes); i++)
add(data.bytes[i]);
} // checksum::add(DWORD)

/****************************************************************************
* checksum::add
* Inputs:
* WORD value:
* Result: void
*
* Effect:
* Adds the bytes of the WORD value to the checksum
****************************************************************************/

void checksum::add(WORD value)
{
union { WORD value; BYTE bytes[2]; } data;
data.value = value;
for(UINT i = 0; i < sizeof(data.bytes); i++)
add(data.bytes[i]);
} // checksum::add(WORD)

/****************************************************************************
* checksum::add
* Inputs:
* BYTE value:
* Result: void
*
* Effect:
* Adds the byte to the checksum
****************************************************************************/

void checksum::add(BYTE value)
{
BYTE cipher = (value ^ (r >> 8));
r = (cipher + r) * c1 + c2;
sum += cipher;
} // checksum::add(BYTE)

/****************************************************************************
* checksum::add
* Inputs:
* const CString & s: String to add
* Result: void
*
* Effect:
* Adds each character of the string to the checksum
****************************************************************************/

void checksum::add(const CString & s)
{
for(int i = 0; i < s.GetLength(); i++)
add((BYTE)s.GetAt(i));
} // checksum::add(CString)

/****************************************************************************
* checksum::add
* Inputs:
* LPBYTE b: pointer to byte array
* UINT length: count
* Result: void
*
* Effect:
* Adds the bytes to the checksum
****************************************************************************/

void checksum::add(LPBYTE b, UINT length)
{
for(UINT i = 0; i < length; i++)
add(b[i]);
} // checksum::add(LPBYTE, UINT)

Copyright © 2001 The Joseph M. Newcomer Co. All Rights Reserved.

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