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

[Aaron Watry]

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