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Re: [Qemu-devel] [PATCH 1/6 v6] target-tilegx: Firstly add TILE-Gx with
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From: |
Richard Henderson |
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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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Date: |
Fri, 20 Mar 2015 10:03:51 -0700 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 |
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~