Re: [PATCH newlib v1 0/4] Add FreeBSD long double functions

[Jeff Johnston <jjohnstn@redhat.com>]

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On Fri, Aug 26, 2022 at 1:45 PM Corinna Vinschen <vinschen@redhat.com>
wrote:

> 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.
> > >
>

Sorry for the late reply.  I agree with your proposal Corinna.

>
> > +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
>
>