As previously discussed
<https://sourceware.org/ml/libc-alpha/2013-10/msg00345.html>, it would
be desirable to be able to use the same version of the soft-fp code in
the Linux kernel as well as in glibc and libgcc (instead of an old
version in the kernel that's missing ten years of bug fixes,
performance improvements and new features), and to that end it is
useful to add to glibc's copy features in the kernel's copy, even when
they are not directly useful in glibc.
To that end, this patch adds one of those features: support for more
precise "invalid" exceptions describing the particular kind of invalid
operation. These are relevant for powerpc emulation, and are also as
described in IEEE 754-2008 as sub-exceptions.
The set of sub-exceptions here is the union of those supported on
powerpc and those from IEEE 754-2008 (the former adds a distinction
between 0/0 and Inf/Inf; the latter adds a distinction between Inf*0
from multiplication and the same from fma). This includes
sub-exceptions for sqrt, conversions to integer and comparisons that
are not supported in the kernel; I see no obvious reason for these
being missing from the kernel support, given that they are supported
on powerpc so accurate powerpc emulation should generate them.
Tested for powerpc-nofpu that the disassembly of installed shared
libraries is unchanged by this patch.
* soft-fp/soft-fp.h (FP_EX_INVALID_SNAN): New macro.
(FP_EX_INVALID_IMZ): Likewise.
(FP_EX_INVALID_IMZ_FMA): Likewise.
(FP_EX_INVALID_ISI): Likewise.
(FP_EX_INVALID_ZDZ): Likewise.
(FP_EX_INVALID_IDI): Likewise.
(FP_EX_INVALID_SQRT): Likewise.
(FP_EX_INVALID_CVI): Likewise.
(FP_EX_INVALID_VC): Likewise.
* soft-fp/op-common.h (_FP_UNPACK_CANONICAL): Specify more precise
"invalid" exceptions.
(_FP_CHECK_SIGNAN_SEMIRAW): Likewise.
(_FP_ADD_INTERNAL): Likewise.
(_FP_MUL): Likewise.
(_FP_FMA): Likewise.
(_FP_DIV): Likewise.
(_FP_CMP_CHECK_NAN): Likewise.
(_FP_SQRT): Likewise.
(_FP_TO_INT): Likewise.
(FP_EXTEND): Likewise.
Continuing the addition of soft-fp features used in the Linux kernel,
this patch adds soft-fp support for FP_DENORM_ZERO (flushing input
subnormal operands to zero of the same sign).
There are some differences from the kernel version. In the kernel,
the "inexact" exception is set when flushing to zero. This does not
appear to match the documented semantics for either of the
architectures (alpha and sh) for which the kernel uses FP_DENORM_ZERO,
so this patch does not set "inexact" in this case. More operations
now use raw or semi-raw unpacking for optimization than did in the
ten-year-old soft-fp version in the kernel, so checks of
FP_DENORM_ZERO are inserted in those operations. They are also
inserted for comparisons (which already used raw unpacking in the old
version) as I believe that's the correct thing to do when input
subnormals are flushed to zero. They are *not* inserted for _FP_NEG.
(If any processors do flush input subnormals to zero for negation, or
otherwise vary from the rules implemented when FP_DENORM_ZERO is set,
further macros for sfp-machine.h to control this may need to be
added.)
Although the addition for comparisons will cause FP_EX_DENORM to be
set in this case, it still won't be set for comparisons involving
subnormals when not flushed to zero. It's quite possible that
accurate emulation of processors that have such an exception for
subnormal operands will require further changes relating to when
FP_EX_DENORM is set (in general, the support for things defined by
IEEE should be considered more reliable and mature than the support
for things outside the scope of IEEE floating point).
Although some processors also have a mode for abrupt underflow -
producing zeroes instead of output subnormals - there is no such mode
in the kernel's soft-fp, so no such mode is added to glibc's soft-fp
(although it could be if someone wanted to emulate such processor
support).
Tested for powerpc-nofpu that the disassembly of installed shared
libraries is unchanged by this patch.
* soft-fp/soft-fp.h (FP_DENORM_ZERO): New macro.
* soft-fp/op-common.h (_FP_UNPACK_CANONICAL): Check
FP_DENORM_ZERO.
(_FP_CHECK_FLUSH_ZERO): New macro.
(_FP_ADD_INTERNAL): Call _FP_CHECK_FLUSH_ZERO.
(_FP_CMP): Likewise.
(_FP_CMP_EQ): Likewise.
(_FP_TO_INT): Do not set inexact for subnormal arguments if
FP_DENORM_ZERO.
(FP_EXTEND): Call _FP_CHECK_FLUSH_ZERO.
(FP_TRUNC): Likewise.
This patch fixes a soft-fp corner case I previously noted in
<https://sourceware.org/ml/libc-alpha/2013-10/msg00349.html>: when
trapping on underflow is enabled, extensions of subnormals from XFmode
to TFmode need to signal underflow because the result is tiny (but
exact, so the underflow flag is not raised unless trapping is
enabled).
To avoid any excess initialization or tests for other cases of
floating-point extensions, a new FP_INIT_TRAPPING_EXCEPTIONS is added
that does the initialization required for this particular case (more
than FP_INIT_EXCEPTIONS, less than FP_INIT_ROUNDMODE, in general), and
FP_NO_EXACT_UNDERFLOW is added to stub out FP_TRAPPING_EXCEPTIONS
tests for those cases of extensions where the test would be dead code,
to avoid any uninitialized variable warnings.
As the relevant case only applies in libgcc, not to any use of soft-fp
in glibc, there is no bug report in Bugzilla and no non-default
definitions of FP_INIT_TRAPPING_EXCEPTIONS are added by the patch. A
testcase will be added to GCC as part of an update of soft-fp in
libgcc once this patch is in libc.
Tested for powerpc-nofpu that the disassembly of installed shared
libraries is unchanged by this patch. Bootstrapped GCC with updated
soft-fp with no regressions on x86_64-unknown-linux-gnu and verified
that a test of the relevant case passes where it failed before.
* soft-fp/op-common.h (FP_EXTEND): When a subnormal input produces
a subnormal result, set the underflow exception if trapping on
underflow is enabled.
* soft-fp/soft-fp.h (FP_INIT_TRAPPING_EXCEPTIONS): New macro.
(FP_INIT_EXCEPTIONS): Default to FP_INIT_TRAPPING_EXCEPTIONS.
[FP_NO_EXACT_UNDERFLOW] (FP_TRAPPING_EXCEPTIONS): Undefine and
redefine to 0.
* soft-fp/extenddftf2.c (FP_NO_EXACT_UNDERFLOW): Define.
* soft-fp/extendsfdf2.c (FP_NO_EXACT_UNDERFLOW): Likewise.
* soft-fp/extendsftf2.c (FP_NO_EXACT_UNDERFLOW): Likewise.
* soft-fp/extendxftf2.c (__extendxftf2): Use
FP_INIT_TRAPPING_EXCEPTIONS instead of FP_INIT_ROUNDMODE.
As noted in
<https://sourceware.org/ml/libc-alpha/2013-10/msg00516.html>, the
soft-fp macro FP_CLEAR_EXCEPTIONS should not be necessary, as soft-fp
code should never set an exception and later clear it.
In fact, all four uses in glibc (for SPARC) are indeed unnecessary:
they appear in files that convert 32-bit or 64-bit integers to IEEE
binary128, an operation that can never raise any exceptions. If this
was intended to enable the compiler to optimize away any FP_FROM_INT
code testing for exceptional cases, we now have a better way of doing
this: defining FP_NO_EXCEPTIONS before including soft-fp.h causes all
code handling exceptions to be stubbed out, and the rounding mode to
be hardwired for round-to-zero, to allow such optimizations for source
files where (a) the operation in question, for the particular types in
question, can never raise exceptions, but (b) some instances of the
operation for other types can, so the macros used in the file do
contain references to rounding or exceptions, albeit dead in that
particular file.
The uses in the Linux kernel are also unnecessary (clearing exceptions
at a point where they are already cleared).
This patch duly removes FP_CLEAR_EXCEPTIONS, making the SPARC code in
question use FP_NO_EXCEPTIONS and stop using exception-related macros.
* soft-fp/soft-fp.h (FP_CLEAR_EXCEPTIONS): Remove macro.
* sysdeps/sparc/sparc32/soft-fp/q_itoq.c: Define FP_NO_EXCEPTIONS.
(_Q_itoq): Do not use FP_DECL_EX, FP_CLEAR_EXCEPTIONS or
FP_HANDLE_EXCEPTIONS.
* sysdeps/sparc/sparc32/soft-fp/q_lltoq.c: Define FP_NO_EXCEPTIONS.
(_Q_lltoq): Do not use FP_DECL_EX, FP_CLEAR_EXCEPTIONS or
FP_HANDLE_EXCEPTIONS.
* sysdeps/sparc/sparc32/soft-fp/q_ulltoq.c: Define FP_NO_EXCEPTIONS.
(_Q_ulltoq): Do not use FP_DECL_EX, FP_CLEAR_EXCEPTIONS or
FP_HANDLE_EXCEPTIONS.
* sysdeps/sparc/sparc32/soft-fp/q_utoq.c: Define FP_NO_EXCEPTIONS.
(_Q_utoq): Do not use FP_DECL_EX, FP_CLEAR_EXCEPTIONS or
FP_HANDLE_EXCEPTIONS.
This patch fixes formatting of comments in soft-fp (in particular, the
normal style in glibc does not have a leading '*' on each line, and
comments should start with capital letters and end with ". */").
Tested for powerpc-nofpu that the disassembly of installed shared
libraries is unchanged by this patch.
* soft-fp/extended.h: Fix comment formatting.
* soft-fp/op-1.h: Likewise.
* soft-fp/op-2.h: Likewise.
* soft-fp/op-4.h: Likewise.
* soft-fp/op-8.h: Likewise.
* soft-fp/op-common.h: Likewise.
* soft-fp/soft-fp.h: Likewise.
IEEE 754-2008 defines two ways in which tiny results can be detected,
"before rounding" (based on the infinite-precision result) and "after
rounding" (based on the result when rounded to normal precision as if
the exponent range were unbounded). All binary operations on an
architecture must use the same choice of how tininess is detected.
soft-fp has so far implemented only before-rounding tininess
detection. This patch adds support for after-rounding tininess
detection. A new macro _FP_TININESS_AFTER_ROUNDING is added that
sfp-machine.h must define (soft-fp is meant to be self-contained so
the existing tininess.h files aren't used here, though the information
going in sfp-machine.h has been taken from them). The soft-fp macros
dealing with raising underflow exceptions then handle the cases where
the choice matters specially, rounding a copy of the input to the
appropriate precision to see if a value that's tiny before rounding
isn't tiny after rounding.
Tested for mips64 using GCC trunk (which now uses soft-fp on MIPS, so
supporting exceptions and rounding modes for long double where not
previously supported - this is the immediate motivation for doing this
patch now) together with (a) a patch to sysdeps/mips/math-tests.h to
enable exceptions / rounding modes tests for long double for GCC 4.9
and later, and (b) corresponding changes applied to libgcc's soft-fp
and sfp-machine.h files. In the libgcc context this is also tested on
x86_64 (also an after-rounding architecture) with testcases for
__float128 that I intend to add to the GCC testsuite when updating
soft-fp there.
(To be clear: this patch does not fix any glibc bugs that were
user-visible in past releases, since after-rounding architectures
didn't use soft-fp in any affected case with support for
floating-point exceptions - so there is no corresponding Bugzilla bug.
Rather, it works together with the GCC changes to use soft-fp on MIPS
to allow previously absent long double functionality to work properly,
and allows soft-fp to be used in glibc on after-rounding architectures
in cases where it couldn't previously be used.)
* soft-fp/op-common.h (_FP_DECL): Mark exponent as possibly
unused.
(_FP_PACK_SEMIRAW): Determine tininess based on rounding shifted
value if _FP_TININESS_AFTER_ROUNDING and unrounded value is in
subnormal range.
(_FP_PACK_CANONICAL): Determine tininess based on rounding to
normal precision if _FP_TININESS_AFTER_ROUNDING and unrounded
value has largest subnormal exponent.
* soft-fp/soft-fp.h [FP_NO_EXCEPTIONS]
(_FP_TININESS_AFTER_ROUNDING): Undefine and redefine to 0.
* sysdeps/aarch64/soft-fp/sfp-machine.h
(_FP_TININESS_AFTER_ROUNDING): New macro.
* sysdeps/alpha/soft-fp/sfp-machine.h
(_FP_TININESS_AFTER_ROUNDING): Likewise.
* sysdeps/arm/soft-fp/sfp-machine.h (_FP_TININESS_AFTER_ROUNDING):
Likewise.
* sysdeps/mips/mips64/soft-fp/sfp-machine.h
(_FP_TININESS_AFTER_ROUNDING): Likewise.
* sysdeps/mips/soft-fp/sfp-machine.h
(_FP_TININESS_AFTER_ROUNDING): Likewise.
* sysdeps/powerpc/soft-fp/sfp-machine.h
(_FP_TININESS_AFTER_ROUNDING): Likewise.
* sysdeps/sh/soft-fp/sfp-machine.h (_FP_TININESS_AFTER_ROUNDING):
Likewise.
* sysdeps/sparc/sparc32/soft-fp/sfp-machine.h
(_FP_TININESS_AFTER_ROUNDING): Likewise.
* sysdeps/sparc/sparc64/soft-fp/sfp-machine.h
(_FP_TININESS_AFTER_ROUNDING): Likewise.
* sysdeps/tile/sfp-machine.h (_FP_TININESS_AFTER_ROUNDING):
Likewise.
* soft-fp/soft-fp.h (FP_CUR_EXCEPTIONS): Define.
(FP_TRAPPING_EXCEPTIONS): Provide default implementation.
* sysdeps/sparc/sparc32/soft-fp/sfp-machine.h
(FP_TRAPPING_EXCEPTIONS): Define.
* sysdeps/sparc/sparc64/soft-fp/sfp-machine.h
(FP_TRAPPING_EXCEPTIONS): Define.
* soft-fp/op-common.h (_FP_PACK_SEMIRAW): Signal underflow for
subnormals only when inexact has been signalled or underflow
exceptions are enabled.
(_FP_PACK_CANONICAL): Likewise.
New macros.
* sysdeps/x86_64/soft-fp/sfp-machine.h: Likewise.
* soft-fp/soft-fp.h: Allow sfp-machine.h to define FP_RND_NEAREST
without defining FP_ROUNDMODE.
2001-07-06 Paul Eggert <eggert@twinsun.com>
* manual/argp.texi: Remove ignored LGPL copyright notice; it's
not appropriate for documentation anyway.
* manual/libc-texinfo.sh: "Library General Public License" ->
"Lesser General Public License".
2001-07-06 Andreas Jaeger <aj@suse.de>
* All files under GPL/LGPL version 2: Place under LGPL version
2.1.
* configure.in: Compute sizeof-long-double.
* configure: Regenerated.
* config.make.in: Make sizeof-long-double available to sub-makes.
In libc/soft-fp/:
* soft-fp.h (_FP_ROUND_ZERO): Cast 0 to void before using it
as a statement.
* sysdeps/powerpc/Makefile (routines): New file.
* sysdeps/powerpc/q_*: New files.
2000-03-03 Geoff Keating <geoffk@cygnus.com>
* configure.in: Compute sizeof-long-double.
* configure: Regenerated.
* config.make.in: Make sizeof-long-double available to sub-makes.
2000-01-04 Andreas Jaeger <aj@suse.de>
* nss/nss_db/dummy-db.h (struct db24): Add missing field flags.
(struct db27): Add missing fields byteswapped, join and flags;
remove wrong member handleq.
(struct dbc27): Correct lock field.
* nss/makedb.c: Remove __P.
2000-01-04 Andreas Jaeger <aj@suse.de>
* nss/nss_db/db-open.c (internal_setent): Check for db_open for
success, fix a memory leak and clean up function.
2000-01-04 Ulrich Drepper <drepper@cygnus.com>
* Makefile (install): Pass $(install_root) to ldconfig.
Patch by Akira YOSHIYAMA <yosshy@tkf.att.ne.jp>.
2000-01-03 Jakub Jelinek <jakub@redhat.com>
* soft-fp/op-1.h: Fix division for machines using not normalizing
version of udiv_qrnnd in longlong.h.
* soft-fp/sysdeps/mips/sfp-machine.h: Likewise.
* soft-fp/sysdeps/mips/mips64/sfp-machine.h: Likewise.
* soft-fp/sysdeps/sparc/sparc64/sfp-machine.h: Likewise.
Patch by Eddie C. Dost <ecd@skynet.be>.
* soft-fp/soft-fp.h (QItype, UQItype): New types used by longlong.h.
2000-01-03 Andreas Schwab <schwab@suse.de>
* sysdeps/generic/dl-sysdep.c: Initialize __libc_multiple_libcs,
needed for change in common symbol handing in newer binutils.
1999-12-29 Ulrich Drepper <drepper@cygnus.com>
* soft-fp/*: Tons of new files to implement floating-point arithmetic
in software.
Contributed by Richard Henderson, Jakub Jelinek and others.
