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Date:      Sun, 10 Nov 2013 10:05:18 +0000
From:      David Chisnall <theraven@FreeBSD.org>
To:        David Schultz <das@FreeBSD.org>
Cc:        "freebsd-numerics@FreeBSD.org" <freebsd-numerics@FreeBSD.org>, Steve Kargl <sgk@troutmask.apl.washington.edu>, Bruce Evans <brde@optusnet.com.au>
Subject:   Re: MUSL math functions
Message-ID:  <15792BD0-C47C-4DCA-A112-D3C54F211E67@FreeBSD.org>
In-Reply-To: <20131108085039.GA1821@zim.MIT.EDU>
References:  <DFD5EA35-ABDA-4A09-BFC7-9452D650C7FE@FreeBSD.org> <20131031133352.GA59918@troutmask.apl.washington.edu> <20131101072032.P1002@besplex.bde.org> <20131108085039.GA1821@zim.MIT.EDU>

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On 8 Nov 2013, at 08:50, David Schultz <das@FreeBSD.ORG> wrote:

> However, several things have happened since then. For one, years
> have passed and there's still quite a bit of work to do. For two,
> the only ld128 platform, sparc64, doesn't look as important as it
> used to be. For a long time, we had trouble even finding a viable
> test machine. Therefore, I think any incremental improvement would
> be welcome -- even if it means doing ld80 only.

The PowerPC SysV ABI says that it's ld128 - we only use 64 bit because of lack of compiler support when the architecture was brought up, every other OS uses 128 bit (although I think PPC 128-bit floats are not quite the same as IEEE 128-bit floats, which may cause some problems).  It's quite likely that we'll change it to ld128 at some point, although that will involve some ABI breakage which is unfortunate.  

ARMv8 is ld128 and, although it support hasn't landed yet (it's under development), it is likely to be a very important platform for FreeBSD in coming years.

MIPS is also ld128 on most systems, but the fact that there is no 128-bit floating point hardware for MIPS (except in one ASE, where there is one 128-bit floating point accumulator register) makes this quite a silly choice, so it will probably stay ld64.

David




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