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[PATCH] Implement fmaf correctly
- From: Jakub Jelinek <jakub at redhat dot com>
- To: libc-alpha at sources dot redhat dot com
- Date: Thu, 7 Oct 2010 11:23:27 +0200
- Subject: [PATCH] Implement fmaf correctly
- Reply-to: Jakub Jelinek <jakub at redhat dot com>
Hi!
This patch implements precise fmaf using double arithmetics
and round to odd to avoid double rounding issues.
I guess PowerPC/IA64 should override it with multiarch or
unconditional assembler implementation (IMHO relying on GCC
to do fma if you write x * y + z is wrong).
fma could be implemented similarly using long double in
ldbl-128/, then we can have some soft-fp implementations
(bugzilla has some from Steven, perhaps we could avoid most
of the additional macros just by doing the round to odd in it),
otherwise Dekker/Knuth algorithms for exact multiplication
and addition to a pair of doubles/long doubles would need to be used,
but then we need to prevent undesirable overflows/underflows.
So, just fmaf for now...
2010-10-07 Jakub Jelinek <jakub@redhat.com>
[BZ #3268]
* math/libm-test.inc (fma_test): Add 2 fmaf tests.
* sysdeps/ieee754/dbl-64/s_fmaf.c: New file.
* sysdeps/i386/i686/multiarch/s_fmaf.c: Include
sysdeps/ieee754/dbl-64/s_fmaf.c instead of math/s_fmaf.c.
* sysdeps/x86_64/multiarch/s_fmaf.c: Likewise.
* include/fenv.h (feupdateenv, fetestexcept): Add libm_hidden_proto.
* math/feupdateenv.c (feupdateenv): Add libm_hidden_ver.
* sysdeps/i386/fpu/feupdateenv.c (feupdateenv): Likewise.
* sysdeps/powerpc/fpu/feupdateenv.c (feupdateenv): Likewise.
* sysdeps/x86_64/fpu/feupdateenv.c (feupdateenv): Likewise.
* sysdeps/sparc/fpu/feupdateenv.c (feupdateenv): Likewise.
* sysdeps/ia64/fpu/feupdateenv.c (feupdateenv): Add libm_hidden_def.
* sysdeps/s390/fpu/feupdateenv.c (feupdateenv): Likewise.
* math/ftestexcept.c (fetestexcept): Likewise.
* sysdeps/ia64/fpu/ftestexcept.c (fetestexcept): Likewise.
* sysdeps/i386/fpu/ftestexcept.c (fetestexcept): Likewise.
* sysdeps/s390/fpu/ftestexcept.c (fetestexcept): Likewise.
* sysdeps/powerpc/fpu/ftestexcept.c (fetestexcept): Likewise.
* sysdeps/x86_64/fpu/ftestexcept.c (fetestexcept): Likewise.
* sysdeps/sparc/fpu/ftestexcept.c (fetestexcept): Likewise.
* sysdeps/sh/sh4/fpu/ftestexcept.c (fetestexcept): Likewise.
--- libc/math/libm-test.inc.jj 2010-05-03 20:18:36.000000000 +0200
+++ libc/math/libm-test.inc 2010-10-07 10:42:13.000000000 +0200
@@ -2789,6 +2789,10 @@ fma_test (void)
TEST_fff_f (fma, minus_infty, minus_infty, minus_infty, nan_value, INVALID_EXCEPTION);
TEST_fff_f (fma, 1.25L, 0.75L, 0.0625L, 1.0L);
+#ifdef TEST_FLOAT
+ TEST_fff_f (fma, 0x1.7ff8p+13, 0x1.000002p+0, 0x1.ffffp-24, 0x1.7ff802p+13);
+ TEST_fff_f (fma, 0x1.fffp+0, 0x1.00001p+0, -0x1.fffp+0, 0x1.fffp-20);
+#endif
END (fma);
}
--- libc/sysdeps/ieee754/dbl-64/s_fmaf.c.jj 2010-10-07 08:20:39.000000000 +0200
+++ libc/sysdeps/ieee754/dbl-64/s_fmaf.c 2010-10-07 10:49:06.000000000 +0200
@@ -0,0 +1,50 @@
+/* Compute x * y + z as ternary operation.
+ Copyright (C) 2010 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+ Contributed by Jakub Jelinek <jakub@redhat.com>, 2010.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, write to the Free
+ Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+ 02111-1307 USA. */
+
+#include <math.h>
+#include <fenv.h>
+#include <ieee754.h>
+
+/* This implementation relies on double being more than twice as
+ precise as float and uses rounding to odd in order to avoid problems
+ with double rounding.
+ See a paper by Boldo and Melquiond:
+ http://www.lri.fr/~melquion/doc/08-tc.pdf */
+
+float
+__fmaf (float x, float y, float z)
+{
+ fenv_t env;
+ /* Multiplication is always exact. */
+ double temp = (double) x * (double) y;
+ union ieee754_double u;
+ feholdexcept (&env);
+ fesetround (FE_TOWARDZERO);
+ /* Perform addition with round to odd. */
+ u.d = temp + (double) z;
+ if ((u.ieee.mantissa1 & 1) == 0 && u.ieee.exponent != 0xff)
+ u.ieee.mantissa1 |= fetestexcept (FE_INEXACT) != 0;
+ feupdateenv (&env);
+ /* And finally truncation with round to nearest. */
+ return (float) u.d;
+}
+#ifndef __fmaf
+weak_alias (__fmaf, fmaf)
+#endif
--- libc/sysdeps/i386/i686/multiarch/s_fmaf.c.jj 2010-05-03 20:18:36.000000000 +0200
+++ libc/sysdeps/i386/i686/multiarch/s_fmaf.c 2010-10-07 10:20:29.000000000 +0200
@@ -33,4 +33,4 @@ weak_alias (__fmaf, fmaf)
# define __fmaf __fmaf_ia32
#endif
-#include <math/s_fmaf.c>
+#include <sysdeps/ieee754/dbl-64/s_fmaf.c>
--- libc/sysdeps/x86_64/multiarch/s_fmaf.c.jj 2009-09-03 12:12:45.000000000 +0200
+++ libc/sysdeps/x86_64/multiarch/s_fmaf.c 2010-10-07 10:20:52.000000000 +0200
@@ -1,5 +1,5 @@
/* FMA version of fmaf.
- Copyright (C) 2009 Free Software Foundation, Inc.
+ Copyright (C) 2009, 2010 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
@@ -39,4 +39,4 @@ weak_alias (__fmaf, fmaf)
# define __fmaf __fmaf_sse2
#endif
-#include <math/s_fmaf.c>
+#include <sysdeps/ieee754/dbl-64/s_fmaf.c>
--- libc/include/fenv.h.jj 2010-02-25 22:43:24.000000000 +0100
+++ libc/include/fenv.h 2010-10-07 10:51:15.000000000 +0200
@@ -17,5 +17,7 @@ libm_hidden_proto (fegetenv)
libm_hidden_proto (fesetenv)
libm_hidden_proto (fesetround)
libm_hidden_proto (feholdexcept)
+libm_hidden_proto (feupdateenv)
+libm_hidden_proto (fetestexcept)
#endif
--- libc/math/feupdateenv.c.jj 2009-05-16 19:23:36.000000000 +0200
+++ libc/math/feupdateenv.c 2010-10-07 10:55:17.000000000 +0200
@@ -1,5 +1,5 @@
/* Install given floating-point environment and raise exceptions.
- Copyright (C) 1997, 1999, 2000 Free Software Foundation, Inc.
+ Copyright (C) 1997, 1999, 2000, 2010 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
@@ -31,6 +31,7 @@ __feupdateenv (const fenv_t *envp)
strong_alias (__feupdateenv, __old_feupdateenv)
compat_symbol (libm, __old_feupdateenv, feupdateenv, GLIBC_2_1);
#endif
+libm_hidden_ver (__feupdateenv, feupdateenv)
versioned_symbol (libm, __feupdateenv, feupdateenv, GLIBC_2_2);
stub_warning (feupdateenv)
--- libc/math/ftestexcept.c.jj 2009-05-16 19:23:36.000000000 +0200
+++ libc/math/ftestexcept.c 2010-10-07 11:00:03.000000000 +0200
@@ -1,5 +1,5 @@
/* Test exception in current environment.
- Copyright (C) 1997 Free Software Foundation, Inc.
+ Copyright (C) 1997, 2010 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
@@ -25,5 +25,6 @@ fetestexcept (int excepts)
{
return 0;
}
+libm_hidden_def (fetestexcept)
stub_warning (fetestexcept)
#include <stub-tag.h>
--- libc/sysdeps/ia64/fpu/feupdateenv.c.jj 2009-05-16 19:23:38.000000000 +0200
+++ libc/sysdeps/ia64/fpu/feupdateenv.c 2010-10-07 10:56:02.000000000 +0200
@@ -1,5 +1,5 @@
/* Install given floating-point environment and raise exceptions.
- Copyright (C) 1997, 2000, 2007 Free Software Foundation, Inc.
+ Copyright (C) 1997, 2000, 2007, 2010 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Christian Boissat <Christian.Boissat@cern.ch>, 1999.
@@ -38,3 +38,4 @@ feupdateenv (const fenv_t *envp)
/* Success. */
return 0;
}
+libm_hidden_def (feupdateenv)
--- libc/sysdeps/ia64/fpu/ftestexcept.c.jj 2009-05-16 19:23:38.000000000 +0200
+++ libc/sysdeps/ia64/fpu/ftestexcept.c 2010-10-07 11:00:12.000000000 +0200
@@ -1,5 +1,5 @@
/* Test exception in current environment.
- Copyright (C) 1997, 1999, 2000 Free Software Foundation, Inc.
+ Copyright (C) 1997, 1999, 2000, 2010 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Christian Boissat <Christian.Boissat@cern.ch>, 1999.
@@ -30,3 +30,4 @@ fetestexcept (int excepts)
return (fpsr >> 13) & excepts & FE_ALL_EXCEPT;
}
+libm_hidden_def (fetestexcept)
--- libc/sysdeps/i386/fpu/feupdateenv.c.jj 2009-05-16 19:23:38.000000000 +0200
+++ libc/sysdeps/i386/fpu/feupdateenv.c 2010-10-07 10:56:54.000000000 +0200
@@ -1,5 +1,5 @@
/* Install given floating-point environment and raise exceptions.
- Copyright (C) 1997,99,2000,01,07 Free Software Foundation, Inc.
+ Copyright (C) 1997,99,2000,01,07,2010 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
@@ -57,4 +57,5 @@ strong_alias (__feupdateenv, __old_feupd
compat_symbol (libm, BP_SYM (__old_feupdateenv), BP_SYM (feupdateenv), GLIBC_2_1);
#endif
+libm_hidden_ver (__feupdateenv, feupdateenv)
versioned_symbol (libm, BP_SYM (__feupdateenv), BP_SYM (feupdateenv), GLIBC_2_2);
--- libc/sysdeps/i386/fpu/ftestexcept.c.jj 2009-05-16 19:23:38.000000000 +0200
+++ libc/sysdeps/i386/fpu/ftestexcept.c 2010-10-07 11:00:19.000000000 +0200
@@ -1,5 +1,5 @@
/* Test exception in current environment.
- Copyright (C) 1997, 2003, 2004 Free Software Foundation, Inc.
+ Copyright (C) 1997, 2003, 2004, 2010 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
@@ -38,3 +38,4 @@ fetestexcept (int excepts)
return (temp | xtemp) & excepts & FE_ALL_EXCEPT;
}
+libm_hidden_def (fetestexcept)
--- libc/sysdeps/s390/fpu/feupdateenv.c.jj 2009-05-16 19:23:42.000000000 +0200
+++ libc/sysdeps/s390/fpu/feupdateenv.c 2010-10-07 10:57:17.000000000 +0200
@@ -1,5 +1,5 @@
/* Install given floating-point environment and raise exceptions.
- Copyright (C) 2000 Free Software Foundation, Inc.
+ Copyright (C) 2000, 2010 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Denis Joseph Barrow (djbarrow@de.ibm.com).
@@ -38,3 +38,4 @@ feupdateenv (const fenv_t *envp)
/* Success. */
return 0;
}
+libm_hidden_def (feupdateenv)
--- libc/sysdeps/s390/fpu/ftestexcept.c.jj 2009-05-16 19:23:42.000000000 +0200
+++ libc/sysdeps/s390/fpu/ftestexcept.c 2010-10-07 11:00:26.000000000 +0200
@@ -1,5 +1,5 @@
/* Test exception in current environment.
- Copyright (C) 2000 Free Software Foundation, Inc.
+ Copyright (C) 2000, 2010 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Denis Joseph Barrow (djbarrow@de.ibm.com).
@@ -31,3 +31,4 @@ fetestexcept (int excepts)
temp = (temp >> FPC_DXC_SHIFT) | (temp >> FPC_FLAGS_SHIFT);
return temp & excepts & FE_ALL_EXCEPT;
}
+libm_hidden_def (fetestexcept)
--- libc/sysdeps/powerpc/fpu/feupdateenv.c.jj 2009-05-16 19:23:39.000000000 +0200
+++ libc/sysdeps/powerpc/fpu/feupdateenv.c 2010-10-07 10:58:01.000000000 +0200
@@ -1,5 +1,5 @@
/* Install given floating-point environment and raise exceptions.
- Copyright (C) 1997, 1999, 2000, 2001, 2007, 2008
+ Copyright (C) 1997, 1999, 2000, 2001, 2007, 2008, 2010
Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
@@ -66,4 +66,5 @@ strong_alias (__feupdateenv, __old_feupd
compat_symbol (libm, BP_SYM (__old_feupdateenv), BP_SYM (feupdateenv), GLIBC_2_1);
#endif
+libm_hidden_ver (__feupdateenv, feupdateenv)
versioned_symbol (libm, BP_SYM (__feupdateenv), BP_SYM (feupdateenv), GLIBC_2_2);
--- libc/sysdeps/powerpc/fpu/ftestexcept.c.jj 2009-05-16 19:23:39.000000000 +0200
+++ libc/sysdeps/powerpc/fpu/ftestexcept.c 2010-10-07 11:00:32.000000000 +0200
@@ -1,5 +1,5 @@
/* Test exception in current environment.
- Copyright (C) 1997 Free Software Foundation, Inc.
+ Copyright (C) 1997, 2010 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
@@ -31,3 +31,4 @@ fetestexcept (int excepts)
just: */
return u.l[1] & excepts;
}
+libm_hidden_def (fetestexcept)
--- libc/sysdeps/x86_64/fpu/feupdateenv.c.jj 2009-05-16 19:23:47.000000000 +0200
+++ libc/sysdeps/x86_64/fpu/feupdateenv.c 2010-10-07 10:58:19.000000000 +0200
@@ -1,5 +1,5 @@
/* Install given floating-point environment and raise exceptions.
- Copyright (C) 1997,99,2000,01,07 Free Software Foundation, Inc.
+ Copyright (C) 1997,99,2000,01,07,2010 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
@@ -48,4 +48,5 @@ strong_alias (__feupdateenv, __old_feupd
compat_symbol (libm, __old_feupdateenv, feupdateenv, GLIBC_2_1);
#endif
+libm_hidden_ver (__feupdateenv, feupdateenv)
versioned_symbol (libm, __feupdateenv, feupdateenv, GLIBC_2_2);
--- libc/sysdeps/x86_64/fpu/ftestexcept.c.jj 2009-05-16 19:23:47.000000000 +0200
+++ libc/sysdeps/x86_64/fpu/ftestexcept.c 2010-10-07 11:00:38.000000000 +0200
@@ -1,5 +1,5 @@
/* Test exception in current environment.
- Copyright (C) 2001 Free Software Foundation, Inc.
+ Copyright (C) 2001, 2010 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
@@ -31,3 +31,4 @@ fetestexcept (int excepts)
return (temp | mxscr) & excepts & FE_ALL_EXCEPT;
}
+libm_hidden_def (fetestexcept)
--- libc/sysdeps/sparc/fpu/feupdateenv.c.jj 2009-05-16 19:23:43.000000000 +0200
+++ libc/sysdeps/sparc/fpu/feupdateenv.c 2010-10-07 10:58:35.000000000 +0200
@@ -1,5 +1,5 @@
/* Install given floating-point environment and raise exceptions.
- Copyright (C) 1997, 1999, 2000 Free Software Foundation, Inc.
+ Copyright (C) 1997, 1999, 2000, 2010 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
@@ -46,4 +46,5 @@ strong_alias (__feupdateenv, __old_feupd
compat_symbol (libm, __old_feupdateenv, feupdateenv, GLIBC_2_1);
#endif
+libm_hidden_ver (__feupdateenv, feupdateenv)
versioned_symbol (libm, __feupdateenv, feupdateenv, GLIBC_2_2);
--- libc/sysdeps/sparc/fpu/ftestexcept.c.jj 2009-05-16 19:23:43.000000000 +0200
+++ libc/sysdeps/sparc/fpu/ftestexcept.c 2010-10-07 11:00:45.000000000 +0200
@@ -1,5 +1,5 @@
/* Test exception in current environment.
- Copyright (C) 1997 Free Software Foundation, Inc.
+ Copyright (C) 1997, 2010 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
@@ -28,3 +28,4 @@ fetestexcept (int excepts)
return tmp & excepts & FE_ALL_EXCEPT;
}
+libm_hidden_def (fetestexcept)
--- libc/sysdeps/sh/sh4/fpu/ftestexcept.c.jj 2009-05-16 19:23:43.000000000 +0200
+++ libc/sysdeps/sh/sh4/fpu/ftestexcept.c 2010-10-07 11:00:52.000000000 +0200
@@ -1,5 +1,5 @@
/* Test exception in current environment.
- Copyright (C) 1997, 1998, 2000 Free Software Foundation, Inc.
+ Copyright (C) 1997, 1998, 2000, 2010 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
@@ -30,3 +30,4 @@ fetestexcept (int excepts)
return temp & excepts & FE_ALL_EXCEPT;
}
+libm_hidden_def (fetestexcept)
Jakub