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 Post subject: D0/D1用途整理
PostPosted: Fri Feb 08, 2013 6:11 pm 
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Joined: Fri Mar 04, 2011 9:36 pm
Posts: 500
(1) D0/D1的V1乘法指令,MULT64,在V2 compiler不會用到,
由MULR64 rt5, ra5, rb5 取代。
Andes Compiler不會產生MULT64指令,這已經被關掉了。也無法由使用者切換。
所以D0/D1在純乘法上,V2之後,其實是用不到的。
(也就是其實MULT64已經phase out了)

(2) D0/D1在V2上,會用到的只有乘加指令。
MADDS64及MADD64等,需要用到D0/D1
簡單的說,如果user只會用到64bit乘法,不會用到64bit乘加,就不用打開D0/D1。
V2有1個32 bit的乘加指令可用,叫MADDR32,
它不會用到D0/D1,不過64bit的MADD64,無對應的GPR指令。
所以若需要MADD64,要打開D0/D1


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