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Re: [qemu-s390x] [Qemu-devel] [PATCH v1 09/41] s390x/tcg: Implement VECT

From: David Hildenbrand
Subject: Re: [qemu-s390x] [Qemu-devel] [PATCH v1 09/41] s390x/tcg: Implement VECTOR CHECKSUM
Date: Tue, 16 Apr 2019 11:13:07 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1

On 16.04.19 11:08, Richard Henderson wrote:
> On 4/15/19 10:58 PM, David Hildenbrand wrote:
>>> You could use
>>>   tcg_gen_add2_i32(sum, tmp, sum, zero, tmp, zero);
>>>   tcg_gen_add_i32(sum, sum, tmp);
>> That makes perfect sense, I will use that for now, thanks!
> Here's a funny one.  We can do this in one operation:
>   tcg_gen_add2_i32(tmp, sum, sum, sum, tmp, tmp);

:D I had to look at it 10 times. Very nice trick.

> The lower (sum+tmp) carries into the upper (sum+tmp).
> We take the upper result and discard the lower.
> r~



David / dhildenb

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