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Subject: Re: [Qemu-devel] [PATCH 1/6 v6] target-tilegx: Firstly add TILE-Gx
 with minimized features
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To: Chen Gang <xili_gchen_5257@hotmail.com>, Peter Maydell <peter.maydell@linaro.org>, Chris Metcalf <cmetcalf@ezchip.com>, =?UTF-8?B?QW5kcmVhcyBGw6RyYmVy?= <afaerber@suse.de>, Riku Voipio <riku.voipio@iki.fi>, "walt@tilera.com" <walt@tilera.com>
Cc: qemu-devel <qemu-devel@nongnu.org>

On 03/18/2015 07:04 PM, Chen Gang wrote:
> For me, I am not quite sure about it, the related functional description
> is:
> 
>   rf[Dest] = signExtend32 ((int32_t) rf[SrcA] * (int32_t) rf[SrcB]);
> 
> Do you mean it is equal to:
> 
>   rf[Dest] = signExtend32 (rf[SrcA] * rf[SrcB]);

Yes, of course.

Think about how multiplication works.  Bit N of the input cannot affect any
output bit in [N-1,0].  Thus the first sign-extend cannot affect the output.


r~