I noticed the COBOL compile generated two MVHHI's to set a fullword field with
a constant value, but did an MVC with an 8-byte constant when setting two
adjacent fullwords.
-----Original Message-----
From: IBM Mainframe Assembler List <ASSEMBLER-LIST@LISTSERV.UGA.EDU> On Behalf
Of Jon Perryman
Sent: Friday, August 22, 2025 00:47
To: ASSEMBLER-LIST@LISTSERV.UGA.EDU
Subject: Re: Execute-Type Instructions
On Fri, 22 Aug 2025 00:27:22 +0000, Ngan, Robert <robert.n...@dxc.com> wrote:
>I noticed this too a while back (wow! 2017),
>>1. The two MVHHI (move halfword immediate to halfword storage)
>>instructions are setting up the edit mask.
>>Note: In my code if I had to move > 2 bytes, I just define a constant. This
>>code is more efficient at the expense of understandability for humans reading
>>it.
You're making this far more difficult than necessary. MVHHI moves exactly 1 by
Here's how I would code it to improve performance and make it readable.
macro ,
&L MOVELIT &DEST,&SOURCE
AIF ('&source'(1,1) NE '''').MVC_&DEST_&SOURCE
AIF (L'&DEST EQ 0).NOMOVE
AIF (L'&DEST EQ 1).MVI
AIF (L'&DEST EQ 2).MVHHI
AIF (L'&DEST GT #).MVC_CONSTANT
&L JAL R1,L&SYSNDX
D&SYSNDX DC CL(L'&DEST)&SOURCE
DS 0H
L&SYSNDX MVC &DEST,0(R1)
MEND ,
Your intention is to efficiently move a constant. Moving an inline constant
avoids the fetch for the constant. Is using a 256 byte inline constant wise?
Someone else will need to advise you on the max acceptable length and accept
the cost of the fetch from the litpool.
