* [Qemu-devel] MIPS FP rounding
@ 2007-09-19 20:41 Daniel Jacobowitz
2007-09-20 17:28 ` [Qemu-devel] " Thiemo Seufer
0 siblings, 1 reply; 3+ messages in thread
From: Daniel Jacobowitz @ 2007-09-19 20:41 UTC (permalink / raw)
To: qemu-devel, Thiemo Seufer
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
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Qemu-devel] Re: MIPS FP rounding
2007-09-19 20:41 [Qemu-devel] MIPS FP rounding Daniel Jacobowitz
@ 2007-09-20 17:28 ` Thiemo Seufer
2007-09-24 13:37 ` Daniel Jacobowitz
0 siblings, 1 reply; 3+ messages in thread
From: Thiemo Seufer @ 2007-09-20 17:28 UTC (permalink / raw)
To: Daniel Jacobowitz; +Cc: qemu-devel
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
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Qemu-devel] Re: MIPS FP rounding
2007-09-20 17:28 ` [Qemu-devel] " Thiemo Seufer
@ 2007-09-24 13:37 ` Daniel Jacobowitz
0 siblings, 0 replies; 3+ messages in thread
From: Daniel Jacobowitz @ 2007-09-24 13:37 UTC (permalink / raw)
To: Thiemo Seufer; +Cc: qemu-devel
On Thu, Sep 20, 2007 at 06:28:25PM +0100, Thiemo Seufer wrote:
> It fixed an internal testcase, I'll have to check what was going
> on there, probably tomorrow.
I don't suppose you've had a chance to look at this?
--
Daniel Jacobowitz
CodeSourcery
^ permalink raw reply [flat|nested] 3+ messages in thread
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2007-09-19 20:41 [Qemu-devel] MIPS FP rounding Daniel Jacobowitz
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