In the patch that I applied on March 2nd, I had code to provide support for
Decimal/_Float128 conversions if the user did not use at least GLIBC 2.32. It
did this by using __ibm128 as an intermediate type. The trouble is __ibm128
cannot represent all of the numbers that _Float128 can, and you lose if you do
this conversion.
This patch removes this support. The dfp-bit.c functions now call the the
__sprintfieee128 and __strtoieee128 functions to do the conversion. If the
user does not have GLIBC, they will get a linker error that these functions do
not exist.
The float128 support functions are only built into the static libgcc, so there
isn't an issue with having references to __strtoieee128 and __sprintfieee128
with older GLIBC libraries.
As an added bonus, this patch eliminates the __sprintfkf function which
included stdio.h to get a definition for the sprintf library function. This
allows for building cross compilers without having to have a target stdio.h
available.
libgcc/
2021-03-29 Michael Meissner <meissner@linux.ibm.com>
* config/rs6000/t-float128 (fp128_decstr_funcs): Delete.
(fp128_ppc_funcs): Do not add $(fp128_decstr_funcs).
(fp128_decstr_objs): Delete.
* dfp-bit.h: Call __sprintfieee128 to do conversions from
_Float128 to a Decimal type. Call __strtoieee128 to do
conversions from a Decimal type to _Float128.
* config/rs6000/_sprintfkf.c: Delete file.
* config/rs6000/_sprintfkf.h: Delete file.
* config/rs6000/_strtokf.c: Delete file.
* config/rs6000/_strtokf.h: Delete file.
This patch implements conversions between _Float128 and the 3 Decimal floating
types. It does this by extendending the dfp-bit conversions to add a new
binary floating point type (KF), and doing the conversions in the same manner
as the other binary/decimal conversions.
For conversions from _Float128 to Decimal, this patch uses a function
(__sprintfkf) instead of the sprintf function to convert long double values to
strings. The __sprintfkf function determines if GLIBC 2.32 or newer is used
and calls the IEEE 128-bit version of sprintf (__sprintfieee128). If the GLIBC
is earlier than 2.32, the code will convert _Float128 to __ibm128 and then use
the normal sprintf to convert this value.
For conversions from Decimal to _Float128, this patch uses a function
(__strtokf) instead of strtold to convert the strings from the Decimal
conversion to long double. The __strtokf function determines if GLIBC 2.32 or
newer is used, and if it is, calls the IEEE 128-bit version (__strtoieee128).
If the GLIBC is earlier than 2.32, the code will call strtold and convert the
__ibm128 value to _Float128.
These functions will primarily be used if/when the default PowerPC long double
type is changed to IEEE 128-bit, but they could also be used if the user
explicitly converts _Float128 to/from a Decimal type.
libgcc/
2021-02-22 Michael Meissner <meissner@linux.ibm.com>
* config/rs6000/_dd_to_kf.c: New file.
* config/rs6000/_kf_to_dd.c: New file.
* config/rs6000/_kf_to_sd.c: New file.
* config/rs6000/_kf_to_td.c: New file.
* config/rs6000/_sd_to_kf.c: New file.
* config/rs6000/_sprintfkf.c: New file.
* config/rs6000/_sprintfkf.h: New file.
* config/rs6000/_strtokf.h: New file.
* config/rs6000/_strtokf.c: New file.
* config/rs6000/_td_to_kf.c: New file.
* config/rs6000/quad-float128.h: Add new declarations.
* config/rs6000/t-float128 (fp128_dec_funcs): New macro.
(fp128_decstr_funcs): New macro.
(ibm128_dec_funcs): New macro.
(fp128_ppc_funcs): Add the new conversions.
(fp128_dec_objs): Force Decimal <-> __float128 conversions to be
compiled with -mabi=ieeelongdouble.
(fp128_decstr_objs): Force __float128 <-> string conversions to be
compiled with -mabi=ibmlongdouble.
(ibm128_dec_objs): Force Decimal <-> __float128 conversions to be
compiled with -mabi=ieeelongdouble.
(FP128_CFLAGS_DECIMAL): New macro.
(IBM128_CFLAGS_DECIMAL): New macro.
* dfp-bit.c (DFP_TO_BFP): Add PowerPC _Float128 support.
(BFP_TO_DFP): Add PowerPC _Float128 support.
* dfp-bit.h (BFP_KIND): Add new binary floating point kind for
IEEE 128-bit floating point.
(DFP_TO_BFP): Add PowerPC _Float128 support.
(BFP_TO_DFP): Add PowerPC _Float128 support.
(BFP_SPRINTF): New macro.
This patch removes the target macro LIBGCC2_LONG_DOUBLE_TYPE_SIZE.
After recent changes, this macro was used in two ways in libgcc: to
determine the mode of long double in dfp-bit.h, and to determine
whether a particular mode has excess precision for use in complex
multiplication.
The former is concerned specifically with long double: it relates to
use of strtold for converting between decimal and binary floating
point. This is replaced by comparing __LDBL_MANT_DIG__ with the
appropriate __LIBGCC_*_MANT_DIG__ macro. The latter is replaced
__LIBGCC_*_EXCESS_PRECISION__ predefined macros.
Remarks:
* Comparing (__LDBL_MANT_DIG__ == __LIBGCC_XF_MANT_DIG__) is more
fragile than it looks; it's possible for XFmode to have 53-bit
mantissa (TARGET_96_ROUND_53_LONG_DOUBLE, on FreeBSD and
DragonFlyBSD 32-bit), in which case such a comparison would not
distinguish XFmode and DFmode as possible modes for long double.
Fortunately, no target supporting that form of XFmode also supports
long double = double (but if some target did, we'd need e.g. an
additional macro giving the exponent range of each mode).
Furthermore, this code doesn't actually get used for x86 (or any
other target with XFmode support), because x86 uses BID not DPD and
BID has its own conversion code (which handles conversions for both
XFmode and TFmode without needing to go via strtold). And FreeBSD
and DragonFlyBSD aren't among the targets with DFP support. So
while in principle this code is fragile and it's a deficiency that
it can't support both XFmode and TFmode at once (something that
can't be solved with the string conversion approach without libc
having TS 18661 functions such as strtof128), all these issues
should not be a problem in practice.
* If other cases of excess precision are supported in future, the code
for defining __LIBGCC_*_EXCESS_PRECISION__ may need updating.
Although the most likely such cases might not actually involve
excess precision for any mode used in libgcc - FLT_EVAL_METHOD being
32 to do _Float16 arithmetic on _Float32 should have the effect of
_Complex _Float16 arithmetic using __mulsc3 and __divsc3, rather
than currently nonexistent __mulhc3 and __divhc3 as in bug 63250 for
ARM.
* As has been noted in the context of simultaneous support for
__float128 and __ibm128 on Power, the semantics of macros such as
LONG_DOUBLE_TYPE_SIZE are problematic because they rely on a
poorly-defined precision value for floating-point modes (which seems
to be intended as the number of significant bits in the
representation, e.g. 80 for XFmode which may be either 12 or 16
bytes) uniquely identifying a mode (although defining an arbitrarily
different value for one of the modes you wish to distinguish may
work as a hack). It would be cleaner to have a target hook that
gives a machine mode directly for float, double and long double,
rather than going via these precision values. By eliminating all
use of these macros (FLOAT_TYPE_SIZE, DOUBLE_TYPE_SIZE,
LONG_DOUBLE_TYPE_SIZE) from code built for the target, this patch
facilitates such a conversion to a hook (which I suppose would take
some suitable enum as an argument to identify which of the three
types to return a mode for).
(The issue of multiple type support for DFP conversions would apply
in that Power case.
<https://gcc.gnu.org/ml/gcc-patches/2014-07/msg01084.html> doesn't
seem to touch on it, but it would seem reasonable to punt on it
initially as hard to fix. There would also be the issue of getting
functions such as __powikf2, __mulkc3, __divkc3 defined, but that's
rather easier to address.)
Bootstrapped with no regressions on x86_64-unknown-linux-gnu.
gcc:
* doc/tm.texi.in (LIBGCC2_LONG_DOUBLE_TYPE_SIZE): Remove.
* doc/tm.texi: Regenerate.
* system.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE): Poison.
* config/alpha/alpha.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE): Remove.
* config/i386/i386-interix.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE):
Remove.
* config/i386/i386.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE): Remove.
* config/i386/rtemself.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE): Remove.
* config/ia64/ia64.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE): Remove.
* config/m68k/m68k.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE): Remove.
* config/m68k/netbsd-elf.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE):
Remove.
* config/mips/mips.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE): Remove.
* config/mips/n32-elf.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE): Remove.
* config/msp430/msp430.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE): Remove.
* config/rl78/rl78.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE): Remove.
* config/rs6000/rs6000.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE): Remove.
* config/rx/rx.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE): Remove.
* config/s390/s390.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE): Remove.
* config/sparc/freebsd.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE): Remove.
* config/sparc/linux.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE): Remove.
* config/sparc/linux64.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE): Remove.
* config/sparc/netbsd-elf.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE):
Remove.
gcc/c-family:
* c-cppbuiltin.c (c_cpp_builtins): Define
__LIBGCC_*_EXCESS_PRECISION__ macros for supported floating-point
modes.
libgcc:
* dfp-bit.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE): Remove.
(__LIBGCC_XF_MANT_DIG__): Define if not already defined.
(LONG_DOUBLE_HAS_XF_MODE): Define in terms of
__LIBGCC_XF_MANT_DIG__.
(__LIBGCC_TF_MANT_DIG__): Define if not already defined.
(LONG_DOUBLE_HAS_TF_MODE): Define in terms of
__LIBGCC_TF_MANT_DIG__.
* libgcc2.c (NOTRUNC): Define in terms of
__LIBGCC_*_EXCESS_PRECISION__, not LIBGCC2_LONG_DOUBLE_TYPE_SIZE.
* libgcc2.h (LIBGCC2_LONG_DOUBLE_TYPE_SIZE): Remove.
From-SVN: r215491
