Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!spool.mu.edu!sdd.hp.com!swrinde!ucsd!ucbvax!CS.NIU.EDU!rickert
From: rickert@CS.NIU.EDU ("Neil Rickert, N Illinois U, CS")
Newsgroups: comp.lang.asm370
Subject: Re: MVCL (was Re: why code in 370 Assembler)
Message-ID: <9104261742.AA22162@ucbvax.Berkeley.EDU>
Date: 26 Apr 91 17:40:41 GMT
References: <9104261709.AA04987@mp.cs.niu.edu>
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: IBM 370 Assembly Programming Discussion List
              <ASM370@OHSTVMA.BITNET>
Distribution: inet
Organization: The Internet
Lines: 22

>Invariably, registers 0, 1, 14, and 15 are available for use in an MVCL

  I usually avoid writing that type of program if I can.

  What if you have a reentrant subroutine, R15 is your base reg, R1 has
parameters, R2-12 are tied up for your computationally intense algorithm, and
the routine will be used heavily enough that you cannot afford the cost of
a GETMAIN?

>instruction -- with no saving/restoring of previous contents.  In fact,
>I rarely see Real Programmers using any other registers with an MVCL!
>
>Practical rule-of-thumb:
>
 Another practical rule of thumb:  If there is any chance whatsoever that
the move will violate the MVCL restrictions on destructive overlap, use
an MVC loop or a Load and Store loop (for aligned numeric data).

 Don't assume that just because the instruction is MVC or MVCL you are dealing
with characters.  It might just be an array of numbers.

 -Neil Rickert