[Libclc-dev] [PATCH v2 16/16] native_powr: Switch implementation to native_exp2 and native_log2

[Jan Vesely via Libclc-dev]

On Mon, 2017-11-13 at 20:50 +0100, Jeroen Ketema wrote:
> This one is not immediately obvious to me. Maybe add some appropriate comment?

it exploits that x == 2^{log2 x} and log2 {x^y} == y * log2 x
thus x^y == 2^{log2 x^y} == 2^{y * log2 x}.
However, it only works for x > 0, which is OK since powr(<0, ...)
should return NaN anyway.
IMO powr was added to allow this kind of expansion instead of more
expensive full pow (which needs to handle negative x).

Jan

> 
> Jeroen
> 
> > On 6 Nov 2017, at 23:15, Jan Vesely via Libclc-dev <libclc-dev at lists.llvm.org> wrote:
> > 
> > Signed-off-by: Jan Vesely <jan.vesely at rutgers.edu>
> > ---
> > sent wrong patch the first time. This one passes the CTS.
> > 
> > Jan
> > 
> > generic/include/clc/math/native_powr.h | 8 +++++++-
> > generic/lib/SOURCES                    | 1 +
> > generic/lib/math/native_powr.cl        | 5 +++++
> > generic/lib/math/native_powr.inc       | 6 ++++++
> > 4 files changed, 19 insertions(+), 1 deletion(-)
> > create mode 100644 generic/lib/math/native_powr.cl
> > create mode 100644 generic/lib/math/native_powr.inc
> > 
> > diff --git a/generic/include/clc/math/native_powr.h b/generic/include/clc/math/native_powr.h
> > index e8a37d9..c31161a 100644
> > --- a/generic/include/clc/math/native_powr.h
> > +++ b/generic/include/clc/math/native_powr.h
> > @@ -1 +1,7 @@
> > -#define native_powr pow
> > +#define __CLC_BODY <clc/math/binary_decl_tt.inc>
> > +#define __CLC_FUNCTION native_powr
> > +
> > +#include <clc/math/gentype.inc>
> > +
> > +#undef __CLC_BODY
> > +#undef __CLC_FUNCTION
> > diff --git a/generic/lib/SOURCES b/generic/lib/SOURCES
> > index 355741c..ad5a743 100644
> > --- a/generic/lib/SOURCES
> > +++ b/generic/lib/SOURCES
> > @@ -127,6 +127,7 @@ math/native_exp2.cl
> > math/native_log.cl
> > math/native_log10.cl
> > math/native_log2.cl
> > +math/native_powr.cl
> > math/native_recip.cl
> > math/native_rsqrt.cl
> > math/native_sin.cl
> > diff --git a/generic/lib/math/native_powr.cl b/generic/lib/math/native_powr.cl
> > new file mode 100644
> > index 0000000..452bc6f
> > --- /dev/null
> > +++ b/generic/lib/math/native_powr.cl
> > @@ -0,0 +1,5 @@
> > +#include <clc/clc.h>
> > +
> > +#define __CLC_BODY <native_powr.inc>
> > +#define __FLOAT_ONLY
> > +#include <clc/math/gentype.inc>
> > diff --git a/generic/lib/math/native_powr.inc b/generic/lib/math/native_powr.inc
> > new file mode 100644
> > index 0000000..841b1ff
> > --- /dev/null
> > +++ b/generic/lib/math/native_powr.inc
> > @@ -0,0 +1,6 @@
> > +_CLC_OVERLOAD _CLC_DEF __CLC_GENTYPE native_powr(__CLC_GENTYPE x, __CLC_GENTYPE y) {
> > +  const __CLC_GENTYPE zero = (__CLC_GENTYPE)0.0f;
> > +  const __CLC_GENTYPE res = native_exp2(y * native_log2(x));
> > +  const __CLC_INTN condnan = isless(x, zero);
> > +  return select(res, (__CLC_GENTYPE)NAN, condnan);
> > +}
> > -- 
> > 2.13.6
> > 
> > _______________________________________________
> > Libclc-dev mailing list
> > Libclc-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/libclc-dev
> 
> 
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