[libclc] r217509 - math: Add acos implementation

[Yaron Keren]

Hi Aaron,

Math functions are usually not implemented as simple math identities, due
ot loss of accuracy and lower performance.
For example, see acos(double)

  http://www.netlib.org/fdlibm/e_acos.c

openlibm ( https://github.com/JuliaLang/openlibm ) is a good reference for
more math functions.

I don't know if this approach is appropriate or applicable for libclc
OpenCL implementation, though.

Yaron


2014-09-10 18:43 GMT+03:00 Aaron Watry <awatry at gmail.com>:

> Author: awatry
> Date: Wed Sep 10 10:43:29 2014
> New Revision: 217509
>
> URL: http://llvm.org/viewvc/llvm-project?rev=217509&view=rev
> Log:
> math: Add acos implementation
>
> Passes the tests that were submitted to the piglit list
>
> Tested on R600 (Pitcairn)
>
> Signed-off-by: Aaron Watry <awatry at gmail.com>
> Reviewed-by: Jan Vesely <jan.vesely at rutgers.edu>
>
> Added:
>     libclc/trunk/generic/include/clc/math/acos.h
>     libclc/trunk/generic/include/clc/math/acos.inc
>     libclc/trunk/generic/lib/math/acos.cl
>     libclc/trunk/generic/lib/math/acos.inc
> Modified:
>     libclc/trunk/generic/include/clc/clc.h
>     libclc/trunk/generic/lib/SOURCES
>
> Modified: libclc/trunk/generic/include/clc/clc.h
> URL:
> http://llvm.org/viewvc/llvm-project/libclc/trunk/generic/include/clc/clc.h?rev=217509&r1=217508&r2=217509&view=diff
>
> ==============================================================================
> --- libclc/trunk/generic/include/clc/clc.h (original)
> +++ libclc/trunk/generic/include/clc/clc.h Wed Sep 10 10:43:29 2014
> @@ -32,6 +32,7 @@
>  #include <clc/workitem/get_group_id.h>
>
>  /* 6.11.2 Math Functions */
> +#include <clc/math/acos.h>
>  #include <clc/math/atan.h>
>  #include <clc/math/atan2.h>
>  #include <clc/math/copysign.h>
>
> Added: libclc/trunk/generic/include/clc/math/acos.h
> URL:
> http://llvm.org/viewvc/llvm-project/libclc/trunk/generic/include/clc/math/acos.h?rev=217509&view=auto
>
> ==============================================================================
> --- libclc/trunk/generic/include/clc/math/acos.h (added)
> +++ libclc/trunk/generic/include/clc/math/acos.h Wed Sep 10 10:43:29 2014
> @@ -0,0 +1,2 @@
> +#define __CLC_BODY <clc/math/acos.inc>
> +#include <clc/math/gentype.inc>
>
> Added: libclc/trunk/generic/include/clc/math/acos.inc
> URL:
> http://llvm.org/viewvc/llvm-project/libclc/trunk/generic/include/clc/math/acos.inc?rev=217509&view=auto
>
> ==============================================================================
> --- libclc/trunk/generic/include/clc/math/acos.inc (added)
> +++ libclc/trunk/generic/include/clc/math/acos.inc Wed Sep 10 10:43:29 2014
> @@ -0,0 +1 @@
> +_CLC_OVERLOAD _CLC_DECL __CLC_GENTYPE acos(__CLC_GENTYPE x);
>
> Modified: libclc/trunk/generic/lib/SOURCES
> URL:
> http://llvm.org/viewvc/llvm-project/libclc/trunk/generic/lib/SOURCES?rev=217509&r1=217508&r2=217509&view=diff
>
> ==============================================================================
> --- libclc/trunk/generic/lib/SOURCES (original)
> +++ libclc/trunk/generic/lib/SOURCES Wed Sep 10 10:43:29 2014
> @@ -29,6 +29,7 @@ integer/sub_sat.cl
>  integer/sub_sat_if.ll
>  integer/sub_sat_impl.ll
>  integer/upsample.cl
> +math/acos.cl
>  math/atan.cl
>  math/atan2.cl
>  math/copysign.cl
>
> Added: libclc/trunk/generic/lib/math/acos.cl
> URL:
> http://llvm.org/viewvc/llvm-project/libclc/trunk/generic/lib/math/acos.cl?rev=217509&view=auto
>
> ==============================================================================
> --- libclc/trunk/generic/lib/math/acos.cl (added)
> +++ libclc/trunk/generic/lib/math/acos.cl Wed Sep 10 10:43:29 2014
> @@ -0,0 +1,8 @@
> +#include <clc/clc.h>
> +
> +#ifdef cl_khr_fp64
> +#pragma OPENCL EXTENSION cl_khr_fp64 : enable
> +#endif
> +
> +#define __CLC_BODY <acos.inc>
> +#include <clc/math/gentype.inc>
>
> Added: libclc/trunk/generic/lib/math/acos.inc
> URL:
> http://llvm.org/viewvc/llvm-project/libclc/trunk/generic/lib/math/acos.inc?rev=217509&view=auto
>
> ==============================================================================
> --- libclc/trunk/generic/lib/math/acos.inc (added)
> +++ libclc/trunk/generic/lib/math/acos.inc Wed Sep 10 10:43:29 2014
> @@ -0,0 +1,21 @@
> +/*
> + * There are multiple formulas for calculating arccosine of x:
> + * 1) acos(x) = (1/2*pi) + i * ln(i*x + sqrt(1-x^2)) (notice the 'i'...)
> + * 2) acos(x) = pi/2 + asin(-x) (asin isn't implemented yet)
> + * 3) acos(x) = pi/2 - asin(x) (ditto)
> + * 4) acos(x) = 2*atan2(sqrt(1-x), sqrt(1+x))
> + * 5) acos(x) = pi/2 - atan2(x, ( sqrt(1-x^2) ) )
> + *
> + * Options 1-3 are not currently usable, #5 generates more concise
> radeonsi
> + * bitcode and assembly than #4 (134 vs 132 instructions on radeonsi), but
> + * precision of #4 may be better.
> + */
> +
> +_CLC_OVERLOAD _CLC_DEF __CLC_GENTYPE acos(__CLC_GENTYPE x) {
> +  return (
> +    (__CLC_GENTYPE) 2.0 * atan2(
> +      sqrt((__CLC_GENTYPE) 1.0 - x),
> +      sqrt((__CLC_GENTYPE) 1.0 + x)
> +    )
> +  );
> +}
>
>
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