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Re: [Qemu-devel] QEMU state of ARM NEON support.
From: |
Juha.Riihimaki |
Subject: |
Re: [Qemu-devel] QEMU state of ARM NEON support. |
Date: |
Thu, 25 Mar 2010 12:04:33 +0100 |
On Mar 25, 2010, at 12:27, ext Dmitry Zhurikhin wrote:
> address@hidden wrote:
>> - vqdmlsl yields different results for some specific input values, however I
>> think QEMU is producing correct results. For example,
>> 1431655765-(2*-32768*-32768)=-715827883 but your reference hardware results
>> say it should be -715827882.
> From what I understand hardware gets such result because saturation occurs on
> the (2*-32768*-32768) step. The result is not 0x80000000 as expected but
> because of overflow is set as the largest 32-bit signed integer 0x7FFFFFFF.
> It
> seems that QEMU just doesn't perform saturation (in this particular case at
> least).
Yes I see, I overlooked the fact that -32768*-32768 changes the sign and so
doubling the result of that overflows the signed 32-bit integer even if the
result still fits in 32 bits. Thanks, I'll fix that as well.
Regards,
Juha