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Hi,
This is my first OpenCL project so I might be doing something wrong but I am having a very strange issue.
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) { printf("BEFORE - %lu\n", n); n = (3 * n) + 1; printf("AFTER - %lu\n", n); } else { n = (3 * n) + 1; } } count = count + 1; } out[id] = count; }
And here is the output:
BEFORE - 1572066143 AFTER - 421231134
To me it looks as if the "n" variable is overflowing but I can't figure out why that is happening as it is a unsigned long.
The really strange thing is if I update the kernel to set the value of 'n' to 1572066143 then it works correctly.
__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) { n = 1572066143; printf("BEFORE - %lu\n", n); n = (3 * n) + 1; printf("AFTER - %lu\n", n); } else { n = (3 * n) + 1; } } count = count + 1; } out[id] = count; }
Output:
BEFORE - 1572066143 AFTER - 4716198430
In addition if I run the exact same code on my AMD GPU then I get the correct value.
Please let us know what Processor, Operating System, Graphics Driver Version, and Tool Version you are using:
Processor: i5 4670K (HD Graphics 4600)
Operating System: Windows 10
Graphics Driver Version: 20.19.15.4300
Tool Version: Intel SDK for OpenCL 5.3.0.713
I have attached a zip file containing the host and kernel code.
Any assistance would be great!
Thanks,
Stephen
- If code is involved, it is great to create a small "Reproducer" sample and attach it to the message in the form of a zip file
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Hi Stephen,
This looks like a bug in the compiler. Thanks for reporting! I will let the driver people know.
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