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Subject: Re: [boost] [compute] Review period starts today December 15, 2014, ends on December 24, 2014
From: Thomas M (firespot71_at_[hidden])
Date: 20141222 03:01:43
On 21/12/2014 23:24, Asbjørn wrote:
> On 21.12.2014 20:39, Kyle Lutz wrote:
>> Strongly disagree, the floatingpoint operations on the device are
>> well defined and their output should be identical to the host results
>> (barring optimizations like "clfastrelaxedmath").
>
> While I agree, I've found Intel's OpenCL CPU device to return results
> which make me think it uses some relaxed math regardless. With NVIDIA
> and AMD I can get (essentially) the same results as reference CPU
> calculations, but with Intel I sometimes get quite large discrepancies.
> Of course, it's possible I'm just doing it wrong...
Intel's OpenCL CPU implementation (it was SDK 2013) is exactly the one
from which I am used to that results normally deviate, quite
considerably indeed.
I don't have it installed on this machine, but Kyle could you run some
kernel code on doubles yourself? My code used basic arithmetic operands,
summed values up (up to tensofthousands) and there were several exp /
log / sqrt along the way. I hadn't set any special compiler flag, surely
not clfastrelaxedmath.
My suspicion was that they use their own math library which provides
highly optimized calculation variants. FWIW I am not even sure if a
plain C++ program compiled with the Intel C++ compiler and linking in
their math library will produce the same results as e.g. MSVC.
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