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Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix
From: |
Mark Cave-Ayland |
Subject: |
Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix |
Date: |
Wed, 04 Nov 2015 23:36:45 +0000 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.8.0 |
On 04/11/15 11:05, Richard Henderson wrote:
> On 11/04/2015 11:45 AM, Paolo Bonzini wrote:
>>>>>>>> int32_t src = rs2 >> (word * 32);
>>>>>>>> - int64_t scaled = src << scale;
>>>>>>>> + int64_t scaled = (int64_t)src << scale;
>>>>>>>> int64_t from_fixed = scaled >> 16;
> ...
>>>
>>> I do think we'd be better served by casting to uint64_t on that line.
>>> Note that fpackfix requires the same correction. And it wouldn't hurt
>>> to cast to uint32_t in fpack16, lest we anger the self-same shifting
>>> gods.
>>
>> Hmmm.. say src = -0x80000000, scale = 1;
>>
>> scaled = (uint64_t)-0x8000000 << 1 = 0xffffffff00000000
>> from_fixed = 0xffffffff00000000 >> 16 = 0x0000ffffffff0000
>>
>> Now from_fixed is positive and you get 32767 instead of -32768. In
>> other words, we would have to cast to uint64_t on the scaled assignment,
>> and back to int64_t on the from_fixed assignment. I must be
>> misunderstanding your suggestion.
>
> int64_t scaled = (uint64_t)src << scale;
>
> I.e. one explicit conversion and one implicit conversion.
I suspect Richard knows more about this part of SPARC emulation than I
do, so I'd be fine with a solution similar to the above if everyone
agress. Let me know if you need me to send a SPARC pull request,
although it will probably be quicker coming from Paolo/Richard at the
moment.
ATB,
Mark.
- Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, (continued)
- Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, Peter Maydell, 2015/11/02
- Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, Paolo Bonzini, 2015/11/02
- Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, Richard Henderson, 2015/11/04
- Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, Paolo Bonzini, 2015/11/04
- Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, Richard Henderson, 2015/11/04
- Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, Paolo Bonzini, 2015/11/04
- Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, Markus Armbruster, 2015/11/04
- Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, Paolo Bonzini, 2015/11/04
- Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, Markus Armbruster, 2015/11/04
- Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, Paolo Bonzini, 2015/11/05
- Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix,
Mark Cave-Ayland <=
- Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, Paolo Bonzini, 2015/11/05
- Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, Richard Henderson, 2015/11/05
- Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, Paolo Bonzini, 2015/11/05
- Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, Richard Henderson, 2015/11/05
- Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, Paolo Bonzini, 2015/11/05
- Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, Mark Cave-Ayland, 2015/11/06
- Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, Paolo Bonzini, 2015/11/06