2013-04-02 13:51:02 +02:00
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/* Internal math stuff. MIPS version.
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2014-01-01 12:03:15 +01:00
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Copyright (C) 2013-2014 Free Software Foundation, Inc.
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2013-04-02 13:51:02 +02:00
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#ifndef _MATH_PRIVATE_H
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MIPS: IEEE 754-2008 NaN encoding support
It has been a long practice for software using IEEE 754 floating-point
arithmetic run on MIPS processors to use an encoding of Not-a-Number
(NaN) data different to one used by software run on other processors.
And as of IEEE 754-2008 revision [1] this encoding does not follow one
recommended in the standard, as specified in section 6.2.1, where it
is stated that quiet NaNs should have the first bit (d1) of their
significand set to 1 while signalling NaNs should have that bit set to
0, but MIPS software interprets the two bits in the opposite manner.
As from revision 3.50 [2][3] the MIPS Architecture provides for
processors that support the IEEE 754-2008 preferred NaN encoding format.
As the two formats (further referred to as "legacy NaN" and "2008 NaN")
are incompatible to each other, tools have to provide support for the
two formats to help people avoid using incompatible binary modules.
The change is comprised of two functional groups of features, both of
which are required for correct support.
1. Dynamic linker support.
To enforce the NaN encoding requirement in dynamic linking a new ELF
file header flag has been defined. This flag is set for 2008-NaN
shared modules and executables and clear for legacy-NaN ones. The
dynamic linker silently ignores any incompatible modules it
encounters in dependency processing.
To avoid unnecessary processing of incompatible modules in the
presence of a shared module cache, a set of new cache flags has been
defined to mark 2008-NaN modules for the three ABIs supported.
Changes to sysdeps/unix/sysv/linux/mips/readelflib.c have been made
following an earlier code quality suggestion made here:
http://sourceware.org/ml/libc-ports/2009-03/msg00036.html
and are therefore a little bit more extensive than the minimum
required.
Finally a new name has been defined for the dynamic linker so that
2008-NaN and legacy-NaN binaries can coexist on a single system that
supports dual-mode operation and that a legacy dynamic linker that
does not support verifying the 2008-NaN ELF file header flag is not
chosen to interpret a 2008-NaN binary by accident.
2. Floating environment support.
IEEE 754-2008 features are controlled in the Floating-Point Control
and Status (FCSR) register and updates are needed to floating
environment support so that the 2008-NaN flag is set correctly and
the kernel default, inferred from the 2008-NaN ELF file header flag
at the time an executable is loaded, respected.
As the NaN encoding format is a property of GCC code generation that is
both a user-selected GCC configuration default and can be overridden
with GCC options, code that needs to know what NaN encoding standard it
has been configured for checks for the __mips_nan2008 macro that is
defined internally by GCC whenever the 2008-NaN mode has been selected.
This mode is determined at the glibc configuration time and therefore a
few consistency checks have been added to catch cases where compilation
flags have been overridden by the user.
The 2008 NaN set of features relies on kernel support as the in-kernel
floating-point emulator needs to be aware of the NaN encoding used even
on hard-float processors and configure the FPU context according to the
value of the 2008 NaN ELF file header flag of the executable being
started. As at this time work on kernel support is still in progress
and the relevant changes have not made their way yet to linux.org master
repository.
Therefore the minimum version supported has been artificially set to
10.0.0 so that 2008-NaN code is not accidentally run on a Linux kernel
that does not suppport it. It is anticipated that the version is
adjusted later on to the actual initial linux.org kernel version to
support this feature. Legacy NaN encoding support is unaffected, older
kernel versions remain supported.
[1] "IEEE Standard for Floating-Point Arithmetic", IEEE Computer
Society, IEEE Std 754-2008, 29 August 2008
[2] "MIPS Architecture For Programmers, Volume I-A: Introduction to the
MIPS32 Architecture", MIPS Technologies, Inc., Document Number:
MD00082, Revision 3.50, September 20, 2012
[3] "MIPS Architecture For Programmers, Volume I-A: Introduction to the
MIPS64 Architecture", MIPS Technologies, Inc., Document Number:
MD00083, Revision 3.50, September 20, 2012
2013-09-18 22:04:27 +02:00
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#ifdef __mips_nan2008
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/* MIPS aligned to IEEE 754-2008. */
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#else
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2013-04-02 13:51:02 +02:00
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/* One of the few architectures where the meaning of the quiet/signaling bit is
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inverse to IEEE 754-2008 (as well as common practice for IEEE 754-1985). */
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MIPS: IEEE 754-2008 NaN encoding support
It has been a long practice for software using IEEE 754 floating-point
arithmetic run on MIPS processors to use an encoding of Not-a-Number
(NaN) data different to one used by software run on other processors.
And as of IEEE 754-2008 revision [1] this encoding does not follow one
recommended in the standard, as specified in section 6.2.1, where it
is stated that quiet NaNs should have the first bit (d1) of their
significand set to 1 while signalling NaNs should have that bit set to
0, but MIPS software interprets the two bits in the opposite manner.
As from revision 3.50 [2][3] the MIPS Architecture provides for
processors that support the IEEE 754-2008 preferred NaN encoding format.
As the two formats (further referred to as "legacy NaN" and "2008 NaN")
are incompatible to each other, tools have to provide support for the
two formats to help people avoid using incompatible binary modules.
The change is comprised of two functional groups of features, both of
which are required for correct support.
1. Dynamic linker support.
To enforce the NaN encoding requirement in dynamic linking a new ELF
file header flag has been defined. This flag is set for 2008-NaN
shared modules and executables and clear for legacy-NaN ones. The
dynamic linker silently ignores any incompatible modules it
encounters in dependency processing.
To avoid unnecessary processing of incompatible modules in the
presence of a shared module cache, a set of new cache flags has been
defined to mark 2008-NaN modules for the three ABIs supported.
Changes to sysdeps/unix/sysv/linux/mips/readelflib.c have been made
following an earlier code quality suggestion made here:
http://sourceware.org/ml/libc-ports/2009-03/msg00036.html
and are therefore a little bit more extensive than the minimum
required.
Finally a new name has been defined for the dynamic linker so that
2008-NaN and legacy-NaN binaries can coexist on a single system that
supports dual-mode operation and that a legacy dynamic linker that
does not support verifying the 2008-NaN ELF file header flag is not
chosen to interpret a 2008-NaN binary by accident.
2. Floating environment support.
IEEE 754-2008 features are controlled in the Floating-Point Control
and Status (FCSR) register and updates are needed to floating
environment support so that the 2008-NaN flag is set correctly and
the kernel default, inferred from the 2008-NaN ELF file header flag
at the time an executable is loaded, respected.
As the NaN encoding format is a property of GCC code generation that is
both a user-selected GCC configuration default and can be overridden
with GCC options, code that needs to know what NaN encoding standard it
has been configured for checks for the __mips_nan2008 macro that is
defined internally by GCC whenever the 2008-NaN mode has been selected.
This mode is determined at the glibc configuration time and therefore a
few consistency checks have been added to catch cases where compilation
flags have been overridden by the user.
The 2008 NaN set of features relies on kernel support as the in-kernel
floating-point emulator needs to be aware of the NaN encoding used even
on hard-float processors and configure the FPU context according to the
value of the 2008 NaN ELF file header flag of the executable being
started. As at this time work on kernel support is still in progress
and the relevant changes have not made their way yet to linux.org master
repository.
Therefore the minimum version supported has been artificially set to
10.0.0 so that 2008-NaN code is not accidentally run on a Linux kernel
that does not suppport it. It is anticipated that the version is
adjusted later on to the actual initial linux.org kernel version to
support this feature. Legacy NaN encoding support is unaffected, older
kernel versions remain supported.
[1] "IEEE Standard for Floating-Point Arithmetic", IEEE Computer
Society, IEEE Std 754-2008, 29 August 2008
[2] "MIPS Architecture For Programmers, Volume I-A: Introduction to the
MIPS32 Architecture", MIPS Technologies, Inc., Document Number:
MD00082, Revision 3.50, September 20, 2012
[3] "MIPS Architecture For Programmers, Volume I-A: Introduction to the
MIPS64 Architecture", MIPS Technologies, Inc., Document Number:
MD00083, Revision 3.50, September 20, 2012
2013-09-18 22:04:27 +02:00
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# define HIGH_ORDER_BIT_IS_SET_FOR_SNAN
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#endif
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2013-04-02 13:51:02 +02:00
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2013-09-23 18:58:30 +02:00
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/* Inline functions to speed up the math library implementation. The
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default versions of these routines are in generic/math_private.h
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and call fesetround, feholdexcept, etc. These routines use inlined
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code instead. */
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#ifdef __mips_hard_float
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# include <fenv.h>
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# include <fenv_libc.h>
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# include <fpu_control.h>
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2014-02-26 23:19:20 +01:00
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# define _FPU_MASK_ALL (_FPU_MASK_V | _FPU_MASK_Z | _FPU_MASK_O \
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|_FPU_MASK_U | _FPU_MASK_I | FE_ALL_EXCEPT)
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2013-09-23 18:58:30 +02:00
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static __always_inline void
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libc_feholdexcept_mips (fenv_t *envp)
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{
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fpu_control_t cw;
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/* Save the current state. */
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_FPU_GETCW (cw);
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envp->__fp_control_register = cw;
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/* Clear all exception enable bits and flags. */
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2014-02-26 23:19:20 +01:00
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cw &= ~(_FPU_MASK_ALL);
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2013-09-23 18:58:30 +02:00
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_FPU_SETCW (cw);
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}
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# define libc_feholdexcept libc_feholdexcept_mips
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# define libc_feholdexceptf libc_feholdexcept_mips
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# define libc_feholdexceptl libc_feholdexcept_mips
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static __always_inline void
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libc_fesetround_mips (int round)
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{
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fpu_control_t cw;
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/* Get current state. */
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_FPU_GETCW (cw);
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/* Set rounding bits. */
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cw &= ~_FPU_RC_MASK;
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cw |= round;
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/* Set new state. */
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_FPU_SETCW (cw);
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}
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# define libc_fesetround libc_fesetround_mips
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# define libc_fesetroundf libc_fesetround_mips
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# define libc_fesetroundl libc_fesetround_mips
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static __always_inline void
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libc_feholdexcept_setround_mips (fenv_t *envp, int round)
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{
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fpu_control_t cw;
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/* Save the current state. */
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_FPU_GETCW (cw);
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envp->__fp_control_register = cw;
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/* Clear all exception enable bits and flags. */
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2014-02-26 23:19:20 +01:00
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cw &= ~(_FPU_MASK_ALL);
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2013-09-23 18:58:30 +02:00
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/* Set rounding bits. */
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cw &= ~_FPU_RC_MASK;
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cw |= round;
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/* Set new state. */
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_FPU_SETCW (cw);
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}
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# define libc_feholdexcept_setround libc_feholdexcept_setround_mips
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# define libc_feholdexcept_setroundf libc_feholdexcept_setround_mips
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# define libc_feholdexcept_setroundl libc_feholdexcept_setround_mips
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2014-02-26 23:19:20 +01:00
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# define libc_feholdsetround libc_feholdexcept_setround_mips
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# define libc_feholdsetroundf libc_feholdexcept_setround_mips
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# define libc_feholdsetroundl libc_feholdexcept_setround_mips
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2013-09-23 18:58:30 +02:00
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static __always_inline void
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libc_fesetenv_mips (fenv_t *envp)
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{
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fpu_control_t cw;
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/* Read current state to flush fpu pipeline. */
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_FPU_GETCW (cw);
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_FPU_SETCW (envp->__fp_control_register);
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}
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# define libc_fesetenv libc_fesetenv_mips
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# define libc_fesetenvf libc_fesetenv_mips
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# define libc_fesetenvl libc_fesetenv_mips
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2014-02-26 23:19:20 +01:00
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static __always_inline int
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libc_feupdateenv_test_mips (fenv_t *envp, int excepts)
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2013-09-23 18:58:30 +02:00
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{
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2014-02-26 23:19:20 +01:00
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/* int ret = fetestexcept (excepts); feupdateenv (envp); return ret; */
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int cw, temp;
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2013-09-23 18:58:30 +02:00
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2014-02-26 23:19:20 +01:00
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/* Get current control word. */
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_FPU_GETCW (cw);
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2013-09-23 18:58:30 +02:00
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/* Set flag bits (which are accumulative), and *also* set the
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cause bits. The setting of the cause bits is what actually causes
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the hardware to generate the exception, if the corresponding enable
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bit is set as well. */
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2014-02-26 23:19:20 +01:00
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temp = cw & FE_ALL_EXCEPT;
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2013-09-23 18:58:30 +02:00
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temp |= envp->__fp_control_register | (temp << CAUSE_SHIFT);
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/* Set new state. */
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_FPU_SETCW (temp);
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2014-02-26 23:19:20 +01:00
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return cw & excepts & FE_ALL_EXCEPT;
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}
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# define libc_feupdateenv_test libc_feupdateenv_test_mips
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# define libc_feupdateenv_testf libc_feupdateenv_test_mips
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# define libc_feupdateenv_testl libc_feupdateenv_test_mips
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static __always_inline void
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libc_feupdateenv_mips (fenv_t *envp)
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{
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libc_feupdateenv_test_mips (envp, 0);
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2013-09-23 18:58:30 +02:00
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}
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# define libc_feupdateenv libc_feupdateenv_mips
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# define libc_feupdateenvf libc_feupdateenv_mips
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# define libc_feupdateenvl libc_feupdateenv_mips
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2014-02-26 23:19:20 +01:00
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# define libc_feresetround libc_feupdateenv_mips
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# define libc_feresetroundf libc_feupdateenv_mips
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# define libc_feresetroundl libc_feupdateenv_mips
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static __always_inline int
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libc_fetestexcept_mips (int excepts)
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{
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int cw;
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/* Get current control word. */
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_FPU_GETCW (cw);
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return cw & excepts & FE_ALL_EXCEPT;
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}
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# define libc_fetestexcept libc_fetestexcept_mips
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# define libc_fetestexceptf libc_fetestexcept_mips
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# define libc_fetestexceptl libc_fetestexcept_mips
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/* Enable support for rounding mode context. */
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# define HAVE_RM_CTX 1
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static __always_inline void
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libc_feholdexcept_setround_mips_ctx (struct rm_ctx *ctx, int round)
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{
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fpu_control_t old, new;
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/* Save the current state. */
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_FPU_GETCW (old);
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ctx->env.__fp_control_register = old;
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/* Clear all exception enable bits and flags. */
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new = old & ~(_FPU_MASK_ALL);
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/* Set rounding bits. */
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new = (new & ~_FPU_RC_MASK) | round;
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if (__glibc_unlikely (new != old))
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{
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_FPU_SETCW (new);
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ctx->updated_status = true;
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}
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else
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ctx->updated_status = false;
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}
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# define libc_feholdexcept_setround_ctx libc_feholdexcept_setround_mips_ctx
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# define libc_feholdexcept_setroundf_ctx libc_feholdexcept_setround_mips_ctx
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# define libc_feholdexcept_setroundl_ctx libc_feholdexcept_setround_mips_ctx
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static __always_inline void
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libc_fesetenv_mips_ctx (struct rm_ctx *ctx)
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{
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libc_fesetenv_mips (&ctx->env);
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}
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# define libc_fesetenv_ctx libc_fesetenv_mips_ctx
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# define libc_fesetenvf_ctx libc_fesetenv_mips_ctx
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# define libc_fesetenvl_ctx libc_fesetenv_mips_ctx
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static __always_inline void
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libc_feupdateenv_mips_ctx (struct rm_ctx *ctx)
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{
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if (__glibc_unlikely (ctx->updated_status))
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libc_feupdateenv_test_mips (&ctx->env, 0);
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}
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# define libc_feupdateenv_ctx libc_feupdateenv_mips_ctx
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# define libc_feupdateenvf_ctx libc_feupdateenv_mips_ctx
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# define libc_feupdateenvl_ctx libc_feupdateenv_mips_ctx
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2014-03-11 23:30:40 +01:00
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# define libc_feresetround_ctx libc_feupdateenv_mips_ctx
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# define libc_feresetroundf_ctx libc_feupdateenv_mips_ctx
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# define libc_feresetroundl_ctx libc_feupdateenv_mips_ctx
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2014-02-26 23:19:20 +01:00
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static __always_inline void
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libc_feholdsetround_mips_ctx (struct rm_ctx *ctx, int round)
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{
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fpu_control_t old, new;
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/* Save the current state. */
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_FPU_GETCW (old);
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ctx->env.__fp_control_register = old;
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/* Set rounding bits. */
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new = (old & ~_FPU_RC_MASK) | round;
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if (__glibc_unlikely (new != old))
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{
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_FPU_SETCW (new);
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ctx->updated_status = true;
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}
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else
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ctx->updated_status = false;
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}
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# define libc_feholdsetround_ctx libc_feholdsetround_mips_ctx
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# define libc_feholdsetroundf_ctx libc_feholdsetround_mips_ctx
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# define libc_feholdsetroundl_ctx libc_feholdsetround_mips_ctx
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2013-09-23 18:58:30 +02:00
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#endif
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2013-04-02 13:51:02 +02:00
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#include_next <math_private.h>
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#endif
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