[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH] target-tilegx: Implement v*add and v*sub instru
|
From: |
Chen Gang |
|
Subject: |
Re: [Qemu-devel] [PATCH] target-tilegx: Implement v*add and v*sub instructions |
|
Date: |
Wed, 23 Sep 2015 05:41:26 +0800 |
|
User-agent: |
Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 |
On 9/22/15 22:45, Richard Henderson wrote:
> On 09/21/2015 10:54 PM, Chen Gang wrote:
>> On 2015年09月19日 10:34, Richard Henderson wrote:
>>>
>>> There's a trick for this that's more efficient for 4 or more elements
>>> per vector (i.e. good for v2 and v1, but not v4):
>>>
>>> a + b = (a & 0x7f7f7f7f) + (b & 0x7f7f7f7f)) ^ ((a ^ b) & 0x80808080)
>>>
>>> a - b = (a | 0x80808080) - (b & 0x7f7f7f7f)) ^ ((a ^ ~b) & 0x80808080)
>>>
>>
>> For me, we need use "(a ^ b) & 0x80..." instead of "(a ^ ~b) & 0x80...".
>
> No. What you did wrong was not use (a | 0x80808080).
>
Oh, sorry. I shall send patch v3 for it. :-)
Thanks.
--
Chen Gang (陈刚)
Open, share, and attitude like air, water, and life which God blessed