UCD3138A64: UCD3138A64 checksum calculation.

To speed up the code, we did it a 32 bit word at a time. It takes them as unsigned 32 bit ints. Here's the code:

void calculate_checksum(register Uint32 *start_address, register Uint32 *end_address)
{
register unsigned long long lcs = long_checksum; //use local register variable for speed.

while(start_address < end_address)
{
lcs = lcs + *start_address ;
lcs = lcs + (Uint32)*(start_address + 1) ;
start_address = start_address + 2;
}
long_checksum = lcs;
}
We do them 2 at a time to speed things up a bit - reduces the loop overhead by a factor of 2.
Note that the result is a long long - 64 bits. So we use 8 bytes to store the checksum.

It gets sped up by a factor of 4. The 32K checksum on the UCD3138 takes about 10 msec, while the 64K one here takes about 5.