alpha: Remove s_trunc{f} implementation (BZ#22666)
Commit Message
As discussed in libc-alpha [1], alpha trunc{f} implementation uses
addt/suc and subt/suc and although the Alpha Architecture
Handbook version 3 states that that ADDx SUBx OUTPUT Exceptions
(B.3 Mapping to IEEE Standard) should not generate Inexact if INE
bit is set, the Alpha 21264 [2] chip manual (A.8 IEEE Floating-Point
Conformance) states that ADDx SUBx OUTPUT does generate inexact
exception for inexact result regardless.
As Joseph noted [3] to correctly fix it on alpha we need to either
avoid the instruction or avoid any inexact bit from it being set
on return from the function (while preserving the inexact bit that
might be set on the entry to the function). The later will result
mf_fpcr followed by a mt_fpcr to get and set the fpcr which will
defeat the optimization itself.
So the patch just remove the alpha optimized and rely on generic
implementation. It fixes the math/test-*-{trunc} on alpha.
[BZ #15479]
[BZ #22666]
* sysdeps/alpha/fpu/s_trunc.c: Remove file.
* sysdeps/alpha/fpu/s_truncf.c: Likewise.
[1] https://sourceware.org/ml/libc-alpha/2018-01/msg00114.html
[2] https://www.star.bnl.gov/public/daq/HARDWARE/21264_data_sheet.pdf
[3] https://sourceware.org/ml/libc-alpha/2018-01/msg00086.html
---
ChangeLog | 5 +++++
sysdeps/alpha/fpu/s_trunc.c | 45 --------------------------------------------
sysdeps/alpha/fpu/s_truncf.c | 44 -------------------------------------------
3 files changed, 5 insertions(+), 89 deletions(-)
delete mode 100644 sysdeps/alpha/fpu/s_trunc.c
delete mode 100644 sysdeps/alpha/fpu/s_truncf.c
Comments
On 01/03/2018 11:14 AM, Adhemerval Zanella wrote:
> As discussed in libc-alpha [1], alpha trunc{f} implementation uses
> addt/suc and subt/suc and although the Alpha Architecture
> Handbook version 3 states that that ADDx SUBx OUTPUT Exceptions
> (B.3 Mapping to IEEE Standard) should not generate Inexact if INE
> bit is set, the Alpha 21264 [2] chip manual (A.8 IEEE Floating-Point
> Conformance) states that ADDx SUBx OUTPUT does generate inexact
> exception for inexact result regardless.
>
> As Joseph noted [3] to correctly fix it on alpha we need to either
> avoid the instruction or avoid any inexact bit from it being set
> on return from the function (while preserving the inexact bit that
> might be set on the entry to the function). The later will result
> mf_fpcr followed by a mt_fpcr to get and set the fpcr which will
> defeat the optimization itself.
>
> So the patch just remove the alpha optimized and rely on generic
> implementation. It fixes the math/test-*-{trunc} on alpha.
>
> [BZ #15479]
> [BZ #22666]
> * sysdeps/alpha/fpu/s_trunc.c: Remove file.
> * sysdeps/alpha/fpu/s_truncf.c: Likewise.
ACK.
r~
deleted file mode 100644
@@ -1,45 +0,0 @@
-/* Copyright (C) 2007-2018 Free Software Foundation, Inc.
- This file is part of the GNU C Library.
- Contributed by Richard Henderson.
-
- 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, see
- <http://www.gnu.org/licenses/>. */
-
-#include <math.h>
-#include <math_ldbl_opt.h>
-#include <libm-alias-double.h>
-
-
-/* Use the chopped rounding mode conversion instructions to implement trunc. */
-
-double
-__trunc (double x)
-{
- double two52 = copysign (0x1.0p52, x);
- double r, tmp;
-
- if (isgreaterequal (fabs (x), 0x1.0p52))
- return x;
-
- __asm (
- "addt/suc %2, %3, %1\n\tsubt/suc %1, %3, %0"
- : "=&f"(r), "=&f"(tmp)
- : "f"(x), "f"(two52));
-
- /* trunc(-0) == -0, and in general we'll always have the same
- sign as our input. */
- return copysign (r, x);
-}
-
-libm_alias_double (__trunc, trunc)
deleted file mode 100644
@@ -1,44 +0,0 @@
-/* Copyright (C) 2007-2018 Free Software Foundation, Inc.
- This file is part of the GNU C Library.
- Contributed by Richard Henderson.
-
- 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, see
- <http://www.gnu.org/licenses/>. */
-
-#include <math.h>
-#include <libm-alias-float.h>
-
-
-/* Use the chopped rounding mode conversion instructions to implement trunc. */
-
-float
-__truncf (float x)
-{
- float two23 = copysignf (0x1.0p23, x);
- float r, tmp;
-
- if (isgreaterequal (fabsf (x), 0x1.0p23))
- return x;
-
- __asm (
- "adds/suc %2, %3, %1\n\tsubs/suc %1, %3, %0"
- : "=&f"(r), "=&f"(tmp)
- : "f"(x), "f"(two23));
-
- /* trunc(-0) == -0, and in general we'll always have the same
- sign as our input. */
- return copysignf (r, x);
-}
-
-libm_alias_float (__trunc, trunc)