Hi,
I posted this question on stackoverflow but I thought this might be a good place to ask as well. integer overflow - openCL Long Overflowing - Stack Overflow
Before I start I am a C beginner and I am trying to do some openCL work which might have been a mistake. Below is my kernel code:
__kernel void collatz(__global int* in, __global int* out)
{
uint id = get_global_id(0);
unsigned long n = (unsigned long)id;
uint count = 0;
while (n > 1) {
if (n % 2 == 0) {
n = n / 2;
} else {
if(n == 1572066143) {
unsigned long test = n;
printf("BEFORE - %lu\n", n);
test = (3 * test) + 1;
printf("AFTER - %lu\n", test);
n = (3 * n) + 1;
} else {
n = (3 * n) + 1;
}
}
count = count + 1;
}
out[id] = count;
}
and the output:
BEFORE - 1572066143
AFTER - 421231134
To me it looks like n is overflowing but I can't figure out why it is happening.
The interesting thing is if I create a new variable to store the same value as n then it seems to work correctly.
unsigned long test = 1572066143;
printf("BEFORE - %lu\n", test);
test = (3 * test) + 1; p
printf("AFTER - %lu\n", test);
Output:
BEFORE - 1572066143
AFTER - 4716198430
As I said I am a C beginner so I could be doing something very stupid!
Any help would be appreciated as I have been pulling my hair out for hours now!
Thanks,
Stephen
