[Libclc-dev] [PATCH] math: Add fmod implementation

[Matt Arsenault]

On Sep 10, 2014, at 1:46 PM, Aaron Watry <awatry at gmail.com> wrote:

> On Wed, Sep 10, 2014 at 12:17 PM, Matt Arsenault
> <Matthew.Arsenault at amd.com> wrote:
>> On 09/10/2014 11:59 AM, Aaron Watry wrote:
>>> 
>>> Passes piglit tests on evergreen (sent to piglit list).
>>> 
>>> Signed-off-by: Aaron Watry <awatry at gmail.com>
>>> ---
>>>  generic/include/clc/clc.h       |  1 +
>>>  generic/include/clc/math/fmod.h |  7 +++++++
>>>  generic/lib/SOURCES             |  1 +
>>>  generic/lib/math/fmod.cl        | 15 +++++++++++++++
>>>  4 files changed, 24 insertions(+)
>>>  create mode 100644 generic/include/clc/math/fmod.h
>>>  create mode 100644 generic/lib/math/fmod.cl
>>> 
>>> diff --git a/generic/include/clc/clc.h b/generic/include/clc/clc.h
>>> index b8c1cb9..94557a1 100644
>>> --- a/generic/include/clc/clc.h
>>> +++ b/generic/include/clc/clc.h
>>> @@ -47,6 +47,7 @@
>>>  #include <clc/math/fma.h>
>>>  #include <clc/math/fmax.h>
>>>  #include <clc/math/fmin.h>
>>> +#include <clc/math/fmod.h>
>>>  #include <clc/math/hypot.h>
>>>  #include <clc/math/log.h>
>>>  #include <clc/math/log2.h>
>>> diff --git a/generic/include/clc/math/fmod.h
>>> b/generic/include/clc/math/fmod.h
>>> new file mode 100644
>>> index 0000000..737679f
>>> --- /dev/null
>>> +++ b/generic/include/clc/math/fmod.h
>>> @@ -0,0 +1,7 @@
>>> +#define __CLC_BODY <clc/math/binary_decl.inc>
>>> +#define __CLC_FUNCTION fmod
>>> +
>>> +#include <clc/math/gentype.inc>
>>> +
>>> +#undef __CLC_BODY
>>> +#undef __CLC_FUNCTION
>>> diff --git a/generic/lib/SOURCES b/generic/lib/SOURCES
>>> index e4ba1d1..45e12aa 100644
>>> --- a/generic/lib/SOURCES
>>> +++ b/generic/lib/SOURCES
>>> @@ -39,6 +39,7 @@ math/exp.cl
>>>  math/exp10.cl
>>>  math/fmax.cl
>>>  math/fmin.cl
>>> +math/fmod.cl
>>>  math/hypot.cl
>>>  math/mad.cl
>>>  math/mix.cl
>>> diff --git a/generic/lib/math/fmod.cl b/generic/lib/math/fmod.cl
>>> new file mode 100644
>>> index 0000000..091035b
>>> --- /dev/null
>>> +++ b/generic/lib/math/fmod.cl
>>> @@ -0,0 +1,15 @@
>>> +#include <clc/clc.h>
>>> +
>>> +#ifdef cl_khr_fp64
>>> +#pragma OPENCL EXTENSION cl_khr_fp64 : enable
>>> +#endif
>>> +
>>> +#define FUNCTION fmod
>>> +#define FUNCTION_IMPL(x, y) ( (x) - (y) * trunc((x) / (y)))
>>> +
>>> +#define __CLC_BODY <binary_impl.inc>
>>> +#include <clc/math/gentype.inc>
>>> +
>>> +#undef __CLC_BODY
>>> +#undef FUNCTION
>>> +#undef FUNCTION_IMPL
>>> \ No newline at end of file
>> 
>> 
>> I think this can use the LLVM frem instruction instead, and would be better
>> expanded in the backend. I have most of a patch that expands ISD::FREM for
>> SI that I forgot about somewhere
>> 
> 
> Hi Matt,
> 
> There's both fmod and remainder functions in the CL built-in library,
> and as near as I can tell, they just differ in how to treat the result
> of x/y:
> 
> From the CL 1.2 spec (6.12.12):
> gentype fmod (gentype x, gentype y) => Modulus. Returns x – y * trunc (x/y).
> 
> gentype remainder (gentype x, gentype y) => Compute the value r such
> that r = x - n*y, where n
> is the integer nearest the exact value of x/y. If there
> are two integers closest to x/y, n shall be the even
> one. If r is zero, it is given the same sign as x.
> 
> Do you happen to know which behavior the frem instruction gives us?
> Truncate or Round half to nearest even?  I'm guessing that one of
> these will be able to use the frem instruction, and the other won't,
> but I haven't checked which is which yet.
> 
> —Aaron

I’m not sure. I was operating under the assumption that frem matches food’s behavior, but I haven’t tested it particularly carefully. x86 lowers frem into calls to fmod, and I assume the OpenCL version behaves the same as libm's

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