Yokogawa µR20000 - Manual (Page 80)

5-4
IM 04P01B01-17E
If the data length of the buffer is odd, a “0” is padded so that it is even. (1) through (6)
are summed as unsigned two-byte integers (unsigned short). If the digit overflows a “1”
is added. Finally, the result is bit-wise inverted.
Sample Program
The sum value is determined using the following sample program, and the calculated
result is returned. The sum determined by the sample program can be compared with
the header sum of the output BINARY header section and the data sum of the output
BINARY footer section.
/*
* Sum Calculation Function (for a 32-bit CPU)
*
* Parameters buff: Pointer to the top of the data on which the sum is calculated
*
len: Length of the data on which the sum is calculated
* Return value: Calculated sum
*/
int cksum(unsigned char *buff, int len)
{
unsigned short *p; /* Pointer to the next two-byte data word in the buffer
that is to be summed. */
unsigned int csum; /* Checksum value */
int i;
int odd;
csum = 0;
/* Initialize. */
odd = len%2; /* Check whether or not the number of data points is
even. */
len >>= 1; /* Determine the number of data points using a “short”
data type. */
p = (unsigned short *)buff;
for(i=0;i /* Sum using an unsigned short data type. */
csum += *p++;
if(odd){ /* When the data length is odd */
union tmp{ /* Pad with a 0, and add to the unsigned short data.
*/
unsigned short s;
unsigned char c[2];
}tmp;
tmp.c[1] = 0;
tmp.c[0] = *((unsigned char *)p);
csum += tmp.s;
}
if((csum = (csum & 0xffff) + ((csum>>16) & 0xffff)) > 0xffff)
/* Add the overflowed digits */
csum = csum - 0xffff; /* If the digit overflows again, add a 1. */
return((~csum) & 0xffff); /* bit inversion */
}
5.1 Response Syntax