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From: rickert@CS.NIU.EDU (Neil Rickert)
Newsgroups: comp.lang.asm370
Subject: Re: MVCL (was Re: why code in 370 Assembler)
Message-ID: <9104261340.AA14703@ucbvax.Berkeley.EDU>
Date: 26 Apr 91 13:36:22 GMT
References: <9104260659.AA07567@ucbvax.Berkeley.EDU>
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Reply-To: IBM 370 Assembly Programming Discussion List
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In article <9104260659.AA07567@ucbvax.Berkeley.EDU> LDW@USCMVSA.BITNET writes:
>
>I've been known to remark that MVCL is an 18 byte RR instruction.
>Let's see now:
>    LA    Rx,source                 4
>    LA    R(x+1),source_length      4
>    LA    Ry,target                 4
>    LA    R(y+1),target_length      4
>    MVCL  Ry,Rx                     2
>                                   ---
>                                   18

 This is why I sometimes prefer an MVC or an MVC/EX loop.

 But of course your 18 bytes is a serious underestimate.  After all you must
first save the current contents of the registers, and later restore them.
If something is really worth doing in assembler, you are probably going to
have all registers tied up, so there just aren't two even/odd pairs readily
available.  MVCL is mostly useful when you need its feature of padding the
destination.


--
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  Neil W. Rickert, Computer Science               <rickert@cs.niu.edu>
  Northern Illinois Univ.
  DeKalb, IL 60115                                   +1-815-753-6940