Thread: Correct way to pass arguments to this function

Hi,

I have a standard Internet Checksum function as follows:

Code:

uint16_t checksum_f(uint16_t *addr, uint32_t length) {

register long sum = 0;
while (length > 1) {
sum += * (unsigned short *) addr++;
length -= 2;
}

if (length > 0)
sum += * (unsigned char *) addr;
while (sum >> 16)
sum = (sum & 0xFFFF) + (sum >> 16);
return ~sum
}

If I wanted to calculate a checksum for the following two things, how would I correctly pass in the parameters to the checksum function:

Code:

typedef struct DATE {

uint16_t year;
uint8_t month;
uint8_t day;
}

Code:

int main () {

DATE tx *txPtr
DATE *rxPtr
uint8_t rx_buffer[100];
uint16_t checksum1, checksum2;

txPtr = &tx; // this will get filled with date information at some point

rxPtr = (DATE *)rx_buffer; // rx buffer contains a date

// now assume there is data in each

// what do you pass in to get the checksum of the data contained in the rx and tx structs?
checksum1 = checksum_f(?, ?);
checksum2 = checksum_f(?, ?);

}

Thanks!

checksum_f(rxPtr , sizeof (DATE));

I suppose

why do you need memcpy? Just a waste of CPU power moreover - if DATE has some padding - you are getting a buffer overrun

Originally Posted by vart

why do you need memcpy? Just a waste of CPU power moreover - if DATE has some padding - you are getting a buffer overrun

Because this will NOT work...

checksum_f(rxPtr , sizeof (DATE));

I suppose

You're trying to use a DATE variable for the 1st parm of the function which requires an unsigned int pointer. Thus, I used memcpy to convert the DATE variable to a variable that is compatible with the function.

You're trying to use a DATE variable

Not DATE but pointer to DATE - so simple casting will be enogh

memcpy just overcomplicates things, and potentially (not very likely but still) could have some side effects due to padding