[PATCH] Fix rounding bug in emulation for double floatoperating

[Kumar Gala]

On Dec 9, 2007, at 11:25 PM, Liu Yu wrote:

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>> -----Original Message-----
>> From: David Gibson [mailto:david at gibson.dropbear.id.au]
>> Sent: Monday, December 10, 2007 12:56 PM
>> To: Liu Yu
>> Cc: linuxppc-dev at ozlabs.org
>> Subject: Re: [PATCH] Fix rounding bug in emulation for double
>> floatoperating
>>
>>
>> On Mon, Dec 10, 2007 at 01:00:52PM +0800, Liu Yu wrote:
>>>
>>> This patch fixes rounding bug in emulation for double float
>> operating on PowerPC platform.
>>>
>>> When pack double float operand, it need to truncate the
>> tail due to the limited precision.
>>> If the truncated part is not zero, the last bit of work bit
>> (totally 3 bits) need to '|' 1.
>>>
>>> This patch is completed in _FP_FRAC_SRS_2(X,N,sz)
>> (arch/powerpc/math-emu/op-2.h).
>>> Originally the code leftwards rotates the operand to just keep the
>>> truncated part, then check whether it is zero. However, the
>> number it
>>> rotates is not correct when N is not smaller than
>> _FP_W_TYPE_SIZE, and it will cause the work bit '|' 1 in the
>> improper case.
>>>
>>> This patch fixes this issue.
>>>
>>> Signed-off-by: Liu Yu <b13201 at freescale.com>
>>
>> Wow someone deciphered the hideous macro hell of the math
>> emulation code enough to fix a bug.  I don't suppose you'd
>> care to fix the millions of warnings that the math-emu code
>> generates...?
>
> Oh, I don't like macro define either. But it's really a bug...


how did you find this?

- k