CODEWITHSUNDEEP
cchecksum
SoftWick
SoftWick

Reputation: 43

What checksum is it and how does it work? [Checksum 32bit]

I'm trying to implement the checksum from the WinHex program, in WinHex and in 010 editor its called

Checksum Uint 32bit

For example, we calculate the checksum of 32byte (represented in HEX) data:

1122334455667788991122334455667711223344556677889911223344556677

The WinHex gives us checksum32 value:

EE65DE86

I was thinking it's just about summing each byte to the previous one:

    unsigned char checksum(unsigned char data[]){
        unsigned char sum = 0;
        int i;
        for(i=0; sizeof(data); i++){
            sum += data[i];
        }
        return -sum;
       }

I tried it, and it gave me the wrong checksum. It is clearly not crc, maybe its Adler or Fletcher or smh else, it's so many checksums variation that kinda difficult to find correct one

Upvotes: 1

Views: 777

Answers (3)

Errorist
Errorist

Reputation: 224

function seems to never returns
it's an infinite loop, or crush
i keeps on increasing till overlaps
besides sizeof(data) is 4, data is a pointer

unsigned char checksum(unsigned char data[]){
    unsigned char sum = 0;
    int i;
    for(i=0; sizeof(data); i++){ // equivalent for(i=0; 4; i++), for(i=0; true; i++)
        sum += data[i];
    }
    return -sum;
   }

also we need data length

unsigned char checksum(unsigned char data[], int data_length){  //<-- added data_length
    int sum = 0; // <-- int instead of unsigned char
    int i;
    for(i=0; i<data_length; i++){  //  as long as i is less than data_length
        sum += data[i];
    }
    return -sum;
   }

Upvotes: 1

SoftWick
SoftWick

Reputation: 43

I have found the solution, thanks to Gerhardh, we need to convert 4bytes into int32 then sum it up

unsigned int checksum( int  data[])
{
    unsigned int sum = 0;
    int i;
    int size;
        
    for(i=0; sizeof(data); i++) {
        sum += data[i];
    }
    return sum;
}

Upvotes: 0

chux
chux

Reputation: 153303

At least this problem:

sizeof(data) below is the size of a pointer and not 0 --> Infinite loop.

unsigned char checksum(unsigned char data[]){
    unsigned char sum = 0;
    int i;
    for(i=0; sizeof(data); i++){
        sum += data[i];
    }
    return -sum;
   }

Function only returns value 0-0xFF, never 0xEE65DE86

Upvotes: 0

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