From: Daniel Jacobowitz <drow@false.org>
To: qemu-devel@nongnu.org, Thiemo Seufer <ths@networkno.de>
Subject: [Qemu-devel] MIPS FP rounding
Date: Wed, 19 Sep 2007 16:41:54 -0400 [thread overview]
Message-ID: <20070919204154.GA13366@caradoc.them.org> (raw)
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.
This shows up in the mul-subnormal-single-1.c test from GCC's ieee.exp.
--
Daniel Jacobowitz
CodeSourcery
next reply other threads:[~2007-09-19 20:41 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-09-19 20:41 Daniel Jacobowitz [this message]
2007-09-20 17:28 ` [Qemu-devel] Re: MIPS FP rounding Thiemo Seufer
2007-09-24 13:37 ` Daniel Jacobowitz
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