[PATCH newlib v1 0/4] Add FreeBSD long double functions
Corinna Vinschen
vinschen@redhat.com
Fri Aug 26 17:45:40 GMT 2022
On Aug 26 10:45, Joel Sherrill wrote:
> On Fri, Aug 26, 2022 at 10:05 AM Corinna Vinschen <vinschen@redhat.com>
> wrote:
> > No, I wrote, create a *single* _fpmath.h file with the massive amount
> > of definitions (*all* seven) based on LDBL_MANT_DIG.
> >
> > There are very few special targets, like x86/x86_64 which need a tweak
> > in the macros, most of the time the macros should be the same.
> >
> > Instead of having 61 files, only have one. In theory there should be
> > only two definitions for targets with LDBL_MANT_DIG == DBL_MANT_DIG
> > to support little and big endian, more shouldn't be required.
> >
> > For all others, we already have *ieee*.h files with matching definitions
> > which can be used as role models for the various (but few) definitions of
> > union IEEEl2bits. See, for instance, newlib/libc/include/machine/ieee.h.
> >
> > > This approach works and doesn't abandon the targets which the
> > > ldbl==dbl method works for.
> >
> > I never said to abandon these targets, but fwiw, I think you're
> > overestimating the complexity to generate a single _fpmath.h
> > file with matching definitions for these targes as well. The
> > information is basically already present in newlib.
> >
> So don't preserve the FreeBSD files as close to a direct copy
> as possible?
We're only talking about the _fpmath.h files, not all the other
files.
If you like, copy over the handful of target-dependent _fpmath.h
files, but *also* add a generic _fpmath.h file for all other
targets, IMHO.
> Maybe I am overestimating it. I just don't see the single _fpmath.h
> to rule them all with confidence like you do. I am not seeing the
> set of parameters in my head which makes this generic with
> some macros.
>
> I'd appreciate help on this.
newlib/libc/include/machine/ieee.h does not help?
Kind of like this:
#if LDBL_MANT_DIG == 24
union IEEEl2bits {
long double e;
# ifdef __IEEE_LITTLE_ENDIAN
struct {
__uint32_t manl :16;
__uint32_t manh :7;
__uint32_t exp :8;
__uint32_t sign :1;
} bits;
struct {
__uint32_t manl :16;
__uint32_t manh :7;
__uint32_t expsign :9;
} xbits;
# else
struct {
__uint32_t sign :1;
__uint32_t exp :8;
__uint32_t manh :7;
__uint32_t manl :16;
} bits;
struct {
__uint32_t expsign :9;
__uint32_t manh :7;
__uint32_t manl :16;
} xbits;
# endif
};
# define LDBL_NBIT 0
# define LDBL_IMPLICIT_NBIT
# define mask_nbit_l(u) ((void)0)
# define LDBL_MANH_SIZE 7
# define LDBL_MANL_SIZE 16
# define LDBL_TO_ARRAY32(u, a) do { \
(a)[0] = (uint32_t)(u).bits.manl \
| ((uint32_t)(u).bits.manh << LDBL_MANL_SIZE) \
(a)[1] = 0; \
} while(0)
#elif LDBL_MANT_DIG == 53
union IEEEl2bits {
long double e;
# ifdef __IEEE_LITTLE_ENDIAN
struct {
__uint64_t manl :32;
__uint64_t manh :20;
__uint64_t exp :11;
__uint64_t sign :1;
} bits;
struct {
__uint64_t manl :32;
__uint64_t manh :20;
__uint64_t expsign :12;
} xbits;
# else
struct {
__uint64_t sign :1;
__uint64_t exp :11;
__uint64_t manh :20;
__uint64_t manl :32;
} bits;
struct {
__uint64_t expsign :12;
__uint64_t manh :20;
__uint64_t manl :32;
} xbits;
# endif
};
# define LDBL_NBIT 0
# define LDBL_IMPLICIT_NBIT
# define mask_nbit_l(u) ((void)0)
# define LDBL_MANH_SIZE 20
# define LDBL_MANL_SIZE 32
# define LDBL_TO_ARRAY32(u, a) do { \
(a)[0] = (uint32_t)(u).bits.manl; \
(a)[1] = (uint32_t)(u).bits.manh; \
} while(0)
#elif LDBL_MANT_DIG == 64
union IEEEl2bits {
long double e;
# ifdef __IEEE_LITTLE_ENDIAN
struct {
__uint64_t manl :32;
__uint64_t manh :32;
__uint64_t exp :15;
__uint64_t sign :1;
__uint64_t junk :16
} bits;
struct {
__uint64_t man :64;
__uint64_t expsign :16;
__uint64_t junk :16
} xbits;
# else
struct {
__uint64_t junk :16
__uint64_t sign :1;
__uint64_t exp :15;
__uint64_t manh :32;
__uint64_t manl :32;
} bits;
struct {
__uint64_t junk :16
__uint64_t expsign :16;
__uint64_t man :64;
} xbits;
# endif
};
# define LDBL_NBIT 0x80000000
# define mask_nbit_l(u) ((u).bits.manh &= ~LDBL_NBIT)
# define LDBL_MANH_SIZE 32
# define LDBL_MANL_SIZE 32
# define LDBL_TO_ARRAY32(u, a) do { \
(a)[0] = (uint32_t)(u).bits.manl; \
(a)[1] = (uint32_t)(u).bits.manh; \
} while(0)
#elif LDBL_MANT_DIG == 113
union IEEEl2bits {
long double e;
# ifdef __IEEE_LITTLE_ENDIAN
struct {
__uint64_t manl :64;
__uint64_t manh :48;
__uint64_t exp :15;
__uint64_t sign :1;
} bits;
struct {
__uint64_t manl :64;
__uint64_t manh :48;
__uint64_t expsign :16;
} xbits;
# else
struct {
__uint64_t sign :1;
__uint64_t exp :15;
__uint64_t manh :48;
__uint64_t manl :64;
} bits;
struct {
__uint64_t expsign :16;
__uint64_t manh :48;
__uint64_t manl :64;
} xbits;
# endif
};
# define LDBL_NBIT 0
# define LDBL_IMPLICIT_NBIT
# define mask_nbit_l(u) ((void)0)
# define LDBL_MANH_SIZE 48
# define LDBL_MANL_SIZE 64
# define LDBL_TO_ARRAY32(u, a) do { \
(a)[0] = (uint32_t)(u).bits.manl; \
(a)[1] = (uint32_t)((u).bits.manl >> 32); \
(a)[2] = (uint32_t)(u).bits.manh; \
(a)[3] = (uint32_t)((u).bits.manh >> 32); \
} while(0)
#endif
There's also a ___IEEE_BYTES_LITTLE_ENDIAN definition which I ignored
for now. Also, the LDBL_MANT_DIG == 64 is defined for x86-only and the
manl/manh fields for LDBL_MANT_DIG == 23 are faked on a 16 bit border
just to have a manl and a manh definition.
I don't claim that it works OOTB with the above, but apart from
the LDBL_NBIT/mask_nbit_l values which differ for x86/x86_64 CPUs,
it should be a good start, I think.
> > Jeff, ping? Your POV would be much appreciated here.
> >
>
> +1
>
> I also have come across there needs to be a way to pick between ld80
> and ld128 headers and implementation files. FreeBSD has them in
> separate directories. Apparently their build system builds common
> plus an architecture specific _fpmath.h and a choice of ld80/ld128
> which adds at least two other header files
But then again, FreeBSD supports ARM and PowerPC, both of which come
with 64 bit long double. So, besides ld80/ld128, there's apparently a
generic implementation, too, to support non-ld80 and non-ld128 long
double, right?
Corinna
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