checksum sender vs reciever?

This is a discussion on checksum sender vs reciever? within the C Programming forums, part of the General Programming Boards category; Have the written this one program & unsure of how to reverse it so that it will have a sum ...

  1. #1
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    Join Date
    Nov 2007
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    checksum sender vs reciever?

    Have the written this one program & unsure of how to reverse it so that it will have a sum check for the reciever & then sum check for sender and compare the 2 sum that will return zero.

    Code:
    /*	Demonstrate the calculation of a checksum using one's
    	complement arithmetic.
    	   Written by:
    	   Date:
    */
    #include <stdio.h>
    #include <string.h>
    #include <pstdint.h>
    
    int main (void)
    {
    //	Local Declarations
    	uint32_t sum      = 0x00000000;
    	uint16_t checksum = 0x0000; 
    
    	char*    str      = "ABCDEFGHI";
    	int      len;
    	int i = 0;
    
    //	Statements
    	len = strlen (str);
    	if (len % 2  == 1)
    	   // Make the number of characters even
    	   len++;
    	for (i = 0; i < len; i += 2)
    	    sum = (sum + str[i] * 256 + str[i + 1]);
    	
    	// Add carries into lower 16 bits
    	while (sum >> 16)
    	   sum = (sum & 0xffff) + (sum >> 16);
    
    	// Complement
    	checksum = ~sum;
    
    	printf ("str:      %s\n",   str);
    	printf ("checksum: %#06X\n", checksum);
    	system("Pause");
    
    	return 0;
    }	// main
    
    /*	Results:
    str:      ABCDEFGHI
    checksum: 0XA5EA
    Please help.
    thank you.

  2. #2
    and the Hat of Guessing tabstop's Avatar
    Join Date
    Nov 2007
    Posts
    14,185
    If you want a comparison that will return 0 when the two numbers are equal, just use subtraction. I don't know what you're asking with the first part: presumably the sender will calculate the checksum and send it, the receiver will calculate the checksum of what was received and will compare that with the received checksum.

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