Tony Thigpen wrote:
I always like to use a second register with a value of +1
QMGREX01 CSECT ,
STM R14,R12,12(R13)
LR R11,R15
LA R14,1
USING QMGREX01,R11,R12
LA R12,4095(R14,R11)
LR R8,R1
USING WORKAREA,R13
It is even move meaningful if using more base registers.
QMGREX01 CSECT ,
STM R14,R12,12(R13)
LR R10,R15
LA R14,1
USING QMGREX01,R10,R11,R12
LA R11,4095(R14,R10)
LA R12,4095(R14,R11)
LR R8,R1
USING WORKAREA,R13
I always use R14 because I always pick it up using LM before branching
back to the caller so it's always fair game at this point in the
program. Any other register would have to be reloaded because the
program might be expecting them to contain something important.
Tony Thigpen
In our beginning Assembler class we present the student with
three models for setting up multiple base registers:
THEPROG CSECT
STM 14,12,12(13)
LR 12,15
USING THEPROG,12,11,10
LM 10,11,ADCON
B AROUND
ADCON DC A(THEPROG+8192,THEPROG+4096)
AROUND DS 0H
----------------
THEPROG CSECT
STM 14,12,12(13)
LR 12,15
USING THEPROG,12,11,10
LA 11,4095(12)
LA 11,1(11)
LA 10,4095(11)
LA 10,1(10)
--------------
THEPROG CSECT
STM 14,12,12(13)
LR 12,15
USING THEPROG,12,11,10
BAS 2,*+8
DC F'4096'
L 2,0(2)
LA 11,0(2,12)
LA 10,0(2,11)
-------------
Each of these works fine, and has its unique set
of teaching points. Next I ask them how to modify
each of these approaches to add an additional
base register: some interesting points about
maintenance come up.
But in the class on programming for z/Architecture
we recommend using LARL for initializing the first
base register; then you may use LAY for subsequent
base registers, although at this point we emphasize
using long-displacement instructions to minimize
the need for multiple base registers.
--
Kind regards,
-Steve Comstock
The Trainer's Friend, Inc.
303-393-8716
http://www.trainersfriend.com
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