Checksum generate

[yazixchi]

Dear all,

i have the problem with checksum generate array data.
This is a sample piece of my program

unsigned char data1[3];
unsigned char data2[4]={0x7F,0xA0,0x00,0x00};

void send(unsigned char *a, unsigned char b, unsigned char *b){

//I do not know what program should i write 
// in this modular, i want to display result of checksum

}

//main program

//call the modular of send
send(data1, 0x33, data2); //

//end of main program

so, how to generate checksum data in modular send?
i want to generate checksum data from array data1, array data2 and 0x33

note : i want to use XOR for checksum the data.

checksum in other words in this case is error detection.
error detection is generated by "exclusive-OR" all bytes data.

give me advice

many thanks

[quzah]

What is a checksum?


Quzah.

[yazixchi]

i mean, error detection.
error detection is generated by "exclusive-OR" all bytes data.

[quzah]

I mean you have to know what you want to do before you can know how to do it. So, what is your checksum supposed to do?


Quzah.

[yazixchi]

I mean you have to know what you want to do before you can know how to do it. So, what is your checksum supposed to do?


Quzah.

ok, i want to XOR these all data

(pseudocode)
write the data1 value
data1[0]=0xFF;
data1[1]=0x0F;
data1[2]=0xEF;

checksum=0x33^data1^data2;

or in manual
checksum=0x33^(0xFF^0x0F^0xEF)^(0x7F^0xA0^0x00^0x0 0);

[CommonTater]

Well... as Quzah is trying to tell you... you can't solve a problem you don't understand...

Generally a checksum is a 16 or 32 bit value formed by doing some sort of math on one or more bytes of data...
There are literally hundreds of different ways to do it... The simplest is to simply add everything up... but it gets way more complex than that.

So... until you understand the problem well enough to explain exactly what you need... there's not much we can do to help you.

[yazixchi]

i mean, If there is an easier method or better way of doing this I would appreciate any help.
my problem is accsess the parameter passing

[tabstop]

Are these unsigned char arrays a fixed size? If not, you will need to also pass the size of those arrays into your function, for there is no way for the function to retrieve that data once it starts. After that a big ol' loop with ^= seems indicated.

[Salem]

> my problem is accsess the parameter passing
Accessing pointers (to arrays) inside a function uses the same notation as if you had the array itself.

void send(unsigned char *a, unsigned char b, unsigned char *b){

//I do not know what program should i write 
// in this modular, i want to display result of checksum
    a[0] = 0xFF;
// or use a for loop to access b[i]
}