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Message-ID: <alpine.LRH.2.02.2002231819190.25353@key0.esi.com.au>
Date: Sun, 23 Feb 2020 19:35:03 +1100 (AEDT)
From: Damian McGuckin <damianm@....com.au>
To: musl@...ts.openwall.com
Subject: Re: Considering x86-64 fenv.s to C
On Sun, 23 Feb 2020, Rich Felker wrote:
> On Sun, Feb 23, 2020 at 04:41:31PM +1100, Damian McGuckin wrote:
>> On Sat, 22 Feb 2020, Rich Felker wrote:
>>
>>> First comment: I couldn't find (maybe I missed?) what you intend fore
>>> the contents of fenv-generic.c and fenv-trivial.c to be, but I don't
>>> see what you want them for. fenv.c should just use the macros/inlines
>>> the fenv_arch.h defines, naturally collapsing to empty functions when
>>> they do nothing (for softfloat archs).
>>
>> I agree. I was seduced by what I thought was a better way.
>>
>> I assume that I can also have a
>>
>> fenv_arch_soft_float.h
>
> I don't follow what this would be for. Presumably
> arch/generic/fenv_arch.h would be empty and the internal header that
> includes fenv_arch.h would define dummy fenv accessor helpers in the
> absence of any defined by fenv_arch.h, or similar.
In
arch/generic/bits/fenv.h
You have
#define FE_ALL_EXCEPT 0
#define FE_TONEAREST 0
typedef unsigned long fexcept_t;
typedef struct { unsigned long __cw; } fenv_t;
#define FE_DFL_ENV ((const fenv_t *) -1)
If you effectively #include this file into the generic code, it should do
as you suggest. I think. See below. It does rely on FE_INVALID not being
defined.
If I fudge it on my X86_64, every routine just does
xorl %eax, %eax
i.e.
return 0
except for
fesetround:
.LFB12:
.cfi_startproc
cmpl $1, %edi
sbbl %eax, %eax
notl %eax
ret
fegetexceptflag:
.LFB18:
.cfi_startproc
movq $0, (%rdi)
xorl %eax, %eax
ret
Also
__flt_rounds()
returns 1 which means round to nearest style which it should.
Regards - Damian
Pacific Engineering Systems International, 277-279 Broadway, Glebe NSW 2037
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