From: Thiemo Seufer <ths@networkno.de>
To: Daniel Jacobowitz <drow@false.org>
Cc: qemu-devel@nongnu.org
Subject: [Qemu-devel] Re: MIPS FP rounding
Date: Thu, 20 Sep 2007 18:28:25 +0100 [thread overview]
Message-ID: <20070920172825.GU9972@networkno.de> (raw)
In-Reply-To: <20070919204154.GA13366@caradoc.them.org>
Daniel Jacobowitz wrote:
> Thiemo, in May you added this:
>
> - update_fcr31(); \
> + update_fcr31(); \
> + if (GET_FP_CAUSE(env->fcr31) & FP_INVALID) \
> + FST2 = 0x7fbfffff; \
> + else if (GET_FP_CAUSE(env->fcr31) & FP_UNDERFLOW) { \
> + if ((env->fcr31 & 0x3) == 0) \
> + FST2 &= 0x80000000ULL; \
> + } \
>
> That last bit says that if underflow is detected and the rounding mode
> is round-to-nearest, return an signed appropriate signed zero. Why?
> The MIPS ISA docs say a rounded result is returned in this case, and
> that's what's in FST2 if that code is removed.
It fixed an internal testcase, I'll have to check what was going
on there, probably tomorrow.
Thiemo
next prev parent reply other threads:[~2007-09-20 17:28 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-09-19 20:41 [Qemu-devel] MIPS FP rounding Daniel Jacobowitz
2007-09-20 17:28 ` Thiemo Seufer [this message]
2007-09-24 13:37 ` [Qemu-devel] " Daniel Jacobowitz
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