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Re: expand and truncate and 387
- To: moshier at mediaone dot net
- Subject: Re: expand and truncate and 387
- From: Jeffrey A Law <law at cygnus dot com>
- Date: Wed, 18 Nov 1998 09:59:38 -0700
- cc: egcs at cygnus dot com, Marc Lehmann <pcg at goof dot com>
- Reply-To: law at cygnus dot com
In message <Pine.LNX.4.03.9811091738520.15420-100000@moshier.ne.mediaone.net>
you write:
>
> > I don't think the x86 backend worries about rounding and truncation on
> > fp->fp conversions.
>
> Assuming the usual long-double precision control setting,
> converting from lower to higher precision is a no-op.
Is that something we can safely assume? I don't think so.
> Converting from higher to lower precision requires the value to
> be stored out to memory and read back in. This actually does
> truncate both the exponent and the significand to the format of the
> narrower width.
OK.
So it seems to me that it really is not safe to ignore extensions & truncations
on the x86, at least it it is not safe to do by default.
jeff