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Re: [Qemu-devel] [PATCH] arm/translate.c: Fix adc_CC/sbc_CC implementati
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From: |
Richard Henderson |
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Subject: |
Re: [Qemu-devel] [PATCH] arm/translate.c: Fix adc_CC/sbc_CC implementation |
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Date: |
Mon, 25 Feb 2013 09:44:10 -0800 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 |
On 02/25/2013 09:15 AM, Laurent Desnogues wrote:
> Looking at the new sbc_cc, it seems that if t0=t1 and CF=1,
> then CF will be cleared while the old code in the helper did
> set it.
Sigh, yes I see it. While the transform
x + ~y + cf
->
x - y + cf - 1
works for the low 32-bits, it gets the carry wrong:
x - x + (1-1) = 0
whereas
x + ~x + 1 = 0xffffffff + 1 = 0x1_00000000
I need to just do exactly what the spec says, not "optimize" it.
r~