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Re: [PATCH] ARM: Optimize IEEE-754 sqrt implementation

From: "Richard Earnshaw (lists)" <Richard dot Earnshaw at arm dot com>
To: Sebastian Huber <sebastian dot huber at embedded-brains dot de>, newlib at sourceware dot org
Date: Tue, 21 Mar 2017 10:08:09 +0000
Subject: Re: [PATCH] ARM: Optimize IEEE-754 sqrt implementation
Authentication-results: sourceware.org; auth=none
References: <1490082540-22841-1-git-send-email-sebastian.huber@embedded-brains.de>

On 21/03/17 07:49, Sebastian Huber wrote:
> Use the vsqrt.f64 and vsqrt.f32 instructions if available.

This is OK (and good catch on the VFP9 erratum).

Thanks.

R.

> ---
>  newlib/libm/machine/arm/Makefile.am |  2 ++
>  newlib/libm/machine/arm/Makefile.in | 17 +++++++++++++-
>  newlib/libm/machine/arm/e_sqrt.c    | 45 +++++++++++++++++++++++++++++++++++++
>  newlib/libm/machine/arm/ef_sqrt.c   | 45 +++++++++++++++++++++++++++++++++++++
>  4 files changed, 108 insertions(+), 1 deletion(-)
>  create mode 100644 newlib/libm/machine/arm/e_sqrt.c
>  create mode 100644 newlib/libm/machine/arm/ef_sqrt.c
> 
> diff --git a/newlib/libm/machine/arm/Makefile.am b/newlib/libm/machine/arm/Makefile.am
> index f0ab84f..1f10a7a 100644
> --- a/newlib/libm/machine/arm/Makefile.am
> +++ b/newlib/libm/machine/arm/Makefile.am
> @@ -6,6 +6,8 @@ INCLUDES = -I $(newlib_basedir)/../newlib/libm/common $(NEWLIB_CFLAGS) \
>  	$(CROSS_CFLAGS) $(TARGET_CFLAGS)
>  
>  LIB_SOURCES = \
> +	e_sqrt.c \
> +	ef_sqrt.c \
>  	s_ceil.c \
>  	s_floor.c \
>  	s_nearbyint.c \
> diff --git a/newlib/libm/machine/arm/Makefile.in b/newlib/libm/machine/arm/Makefile.in
> index 9b27356..5088db8 100644
> --- a/newlib/libm/machine/arm/Makefile.in
> +++ b/newlib/libm/machine/arm/Makefile.in
> @@ -70,7 +70,8 @@ LIBRARIES = $(noinst_LIBRARIES)
>  ARFLAGS = cru
>  lib_a_AR = $(AR) $(ARFLAGS)
>  lib_a_LIBADD =
> -am__objects_1 = lib_a-s_ceil.$(OBJEXT) lib_a-s_floor.$(OBJEXT) \
> +am__objects_1 = lib_a-e_sqrt.$(OBJEXT) lib_a-ef_sqrt.$(OBJEXT) \
> +	lib_a-s_ceil.$(OBJEXT) lib_a-s_floor.$(OBJEXT) \
>  	lib_a-s_nearbyint.$(OBJEXT) lib_a-s_rint.$(OBJEXT) \
>  	lib_a-s_round.$(OBJEXT) lib_a-s_trunc.$(OBJEXT) \
>  	lib_a-sf_ceil.$(OBJEXT) lib_a-sf_floor.$(OBJEXT) \
> @@ -202,6 +203,8 @@ INCLUDES = -I $(newlib_basedir)/../newlib/libm/common $(NEWLIB_CFLAGS) \
>  	$(CROSS_CFLAGS) $(TARGET_CFLAGS)
>  
>  LIB_SOURCES = \
> +	e_sqrt.c \
> +	ef_sqrt.c \
>  	s_ceil.c \
>  	s_floor.c \
>  	s_nearbyint.c \
> @@ -291,6 +294,18 @@ distclean-compile:
>  .c.obj:
>  	$(COMPILE) -c `$(CYGPATH_W) '$<'`
>  
> +lib_a-e_sqrt.o: e_sqrt.c
> +	$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(AM_CPPFLAGS) $(CPPFLAGS) $(lib_a_CFLAGS) $(CFLAGS) -c -o lib_a-e_sqrt.o `test -f 'e_sqrt.c' || echo '$(srcdir)/'`e_sqrt.c
> +
> +lib_a-e_sqrt.obj: e_sqrt.c
> +	$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(AM_CPPFLAGS) $(CPPFLAGS) $(lib_a_CFLAGS) $(CFLAGS) -c -o lib_a-e_sqrt.obj `if test -f 'e_sqrt.c'; then $(CYGPATH_W) 'e_sqrt.c'; else $(CYGPATH_W) '$(srcdir)/e_sqrt.c'; fi`
> +
> +lib_a-ef_sqrt.o: ef_sqrt.c
> +	$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(AM_CPPFLAGS) $(CPPFLAGS) $(lib_a_CFLAGS) $(CFLAGS) -c -o lib_a-ef_sqrt.o `test -f 'ef_sqrt.c' || echo '$(srcdir)/'`ef_sqrt.c
> +
> +lib_a-ef_sqrt.obj: ef_sqrt.c
> +	$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(AM_CPPFLAGS) $(CPPFLAGS) $(lib_a_CFLAGS) $(CFLAGS) -c -o lib_a-ef_sqrt.obj `if test -f 'ef_sqrt.c'; then $(CYGPATH_W) 'ef_sqrt.c'; else $(CYGPATH_W) '$(srcdir)/ef_sqrt.c'; fi`
> +
>  lib_a-s_ceil.o: s_ceil.c
>  	$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(AM_CPPFLAGS) $(CPPFLAGS) $(lib_a_CFLAGS) $(CFLAGS) -c -o lib_a-s_ceil.o `test -f 's_ceil.c' || echo '$(srcdir)/'`s_ceil.c
>  
> diff --git a/newlib/libm/machine/arm/e_sqrt.c b/newlib/libm/machine/arm/e_sqrt.c
> new file mode 100644
> index 0000000..8754b9f
> --- /dev/null
> +++ b/newlib/libm/machine/arm/e_sqrt.c
> @@ -0,0 +1,45 @@
> +/*-
> + * Copyright (c) 2017 embedded brains GmbH
> + * All rights reserved.
> + *
> + * Redistribution and use in source and binary forms, with or without
> + * modification, are permitted provided that the following conditions
> + * are met:
> + * 1. Redistributions of source code must retain the above copyright
> + *    notice, this list of conditions and the following disclaimer.
> + * 2. Redistributions in binary form must reproduce the above copyright
> + *    notice, this list of conditions and the following disclaimer in the
> + *    documentation and/or other materials provided with the distribution.
> + *
> + * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
> + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
> + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
> + * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
> + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
> + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
> + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
> + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
> + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
> + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
> + * SUCH DAMAGE.
> + */
> +
> +#if __ARM_FP & 0x8
> +#include <math.h>
> +
> +double
> +__ieee754_sqrt(double x)
> +{
> +	double result;
> +#if __ARM_ARCH >= 6
> +	asm ("vsqrt.f64 %P0, %P1" : "=w" (result) : "w" (x));
> +#else
> +	/* VFP9 Erratum 760019, see GCC sources "gcc/config/arm/vfp.md" */
> +	asm ("vsqrt.f64 %P0, %P1" : "=&w" (result) : "w" (x));
> +#endif
> +	return result;
> +}
> +
> +#else
> +#include "../../math/e_sqrt.c"
> +#endif
> diff --git a/newlib/libm/machine/arm/ef_sqrt.c b/newlib/libm/machine/arm/ef_sqrt.c
> new file mode 100644
> index 0000000..81c29f1
> --- /dev/null
> +++ b/newlib/libm/machine/arm/ef_sqrt.c
> @@ -0,0 +1,45 @@
> +/*-
> + * Copyright (c) 2017 embedded brains GmbH
> + * All rights reserved.
> + *
> + * Redistribution and use in source and binary forms, with or without
> + * modification, are permitted provided that the following conditions
> + * are met:
> + * 1. Redistributions of source code must retain the above copyright
> + *    notice, this list of conditions and the following disclaimer.
> + * 2. Redistributions in binary form must reproduce the above copyright
> + *    notice, this list of conditions and the following disclaimer in the
> + *    documentation and/or other materials provided with the distribution.
> + *
> + * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
> + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
> + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
> + * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
> + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
> + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
> + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
> + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
> + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
> + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
> + * SUCH DAMAGE.
> + */
> +
> +#if __ARM_FP & 0x4
> +#include <math.h>
> +
> +float
> +__ieee754_sqrtf(float x)
> +{
> +	float result;
> +#if __ARM_ARCH >= 6
> +	asm ("vsqrt.f32 %0, %1" : "=w" (result) : "w" (x));
> +#else
> +	/* VFP9 Erratum 760019, see GCC sources "gcc/config/arm/vfp.md" */
> +	asm ("vsqrt.f32 %0, %1" : "=&w" (result) : "w" (x));
> +#endif
> +	return result;
> +}
> +
> +#else
> +#include "../../math/ef_sqrt.c"
> +#endif
>

References:
- [PATCH] ARM: Optimize IEEE-754 sqrt implementation
  - From: Sebastian Huber

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