gcc 11.1.0: printf("%.43f\n", 0x1.52f8a8e32e982p-140): printed value is incorrectly rounded

[Takashi Yano]

On Sun, 28 Nov 2021 21:38:39 +0900
Takashi Yano wrote:
> On Sun, 28 Nov 2021 16:43:11 +0900
> Takashi Yano wrote:
> > On Thu, 4 Nov 2021 13:24:42 +0100
> > Corinna Vinschen wrote:
> > > However, a much better fix would be to switch to gdtoa, as the BSDs and
> > > Mingw64 do.
> > 
> > I have tried to import gdtoa into newlib from OpenBSD.
> > 
> > gdtoa seems to use malloc much, so it may not work in some of
> > platforms due to insufficient heap. Therefore, new ldtoa.c tries
> > gdtoa first and fallbacks to legacy ldtoa if gdtoa fails.
> > 
> > To import gdtoa to newlib, I did:
> > 1) Create "machine/ieee.h" which conditionally defines ieee_ext
> >    structure and EXT_TO_ARRAY32() macro depend on architecture.
> > 2) Create arith.h which reflects endian of architecture.
> > 3) Merge gdtoa.h with OpenBSD's gdtoa.h. __BEGIN_HIDDEN_DECLS,
> >    __END_HIDDEN_DECLS, PROTO_NORMAL() and DEF_STRONG() are
> >    defined as dummy in this header.
> > 4) Replace malloc()/free() with _malloc_r()/_free_r().
> > 5) Implement ACQUIRE_DTOA_LOCK() and FREE_DTOA_LOCK() macros
> >    using "sys/lock.h" for multi-threading environment.
> > 6) Remove inclusion of "gd_qnan.h" which is not used.
> > 
> > Please see attached patch for more details.
> > 
> > I confirmed this works nicely with cygwin. Moreover, it is much
> > faster than legacy ldtoa (more than 4 times faster).
> > 
> > However, this may break some other supported platforms.
> > 
> > Could anyone please check this?
> 
> Ah, in "machine/ieee.h", struct ieee_ext definition for
> LDBL_MANT_DIG==64 and __IEEE_BIG_ENDIAN case, is obviously
> wrong. 

Fixed.

-- 
Takashi Yano <takashi.yano@nifty.ne.jp>
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