I was looking at this very thing recently. This response is in multiple parts
due to listserv restrictions.
I got curious about what the compiler was doing for this line of code:
10 SEQ-NUMBER-PCER PIC S9(4) COMP.
10 sequence-convert-1-w pic zz9.
move seq-number-pcer to sequence-convert-1-w
This is moving a halfword binary field to 3 bytes zoned decimal, but edited
with zero suppression.
The way I was taught to do it was how it does it in z/OS Enterprise COBOL v4:
LH 0,1494(0,7) SEQ-NUMBER-PCER
CVD 0,1536(0,13) TS2=16
ZAP 1528(2,13),1542(2,13) TS2=8
MVC 1520(4,13),2073(5) TS2=0
ED 1520(4,13),1528(13) TS2=0
MVC 915(3,7),1521(13) SEQUENCE-CONVERT-1-W
1. LH loads the halfword binary field into register 0.
2. CVD converts it from binary to packed decimal.
3. ZAP copies it; I'm not sure why.
Maybe the ED instruction is restrictive on what are allowable sign nibbles, and
the ZAP is ensuring that they are valid: x'0D' or x'0C'
4. MVC is setting up for the ED command: it is establishing an edit mask
that will tell the ED command how to edit the field.
5. ED is applying the edit mask to the (copied) packed field, resulting in
the edited display field.
6. MVC is moving (copying) the result to the destination field.
Seems pretty simple.
[to be continued, the listserv 250 line limit is brutal]
-----Original Message-----
From: IBM Mainframe Assembler List <ASSEMBLER-LIST@LISTSERV.UGA.EDU> On Behalf
Of Ngan, Robert
Sent: Wednesday, August 20, 2025 1:51 PM
To: ASSEMBLER-LIST@LISTSERV.UGA.EDU
Subject: Re: Execute-Type Instructions
Speaking of optimizations, a while back I noticed the COBOL compiler generated
the following code to edit a PIC 9(4) BINARY value into a PIX ZZZZ9 field
MVC 496(6,R13),1851(R3) # TS2=119 +185
LLH R2,8(,R2) # U010-CO-ID
VCVD VRF16,R2,0x85,0
VUPKZ VRF16,1005(,R13),0x4 #
CDZT FP0,1005(5,R13),0x8 #
ESDTR R2,FP0
VL VRF17,2224(,R3),0 #
VL VRF18,2240(,R3),0 #
VLRL VRF20,1005(,R13),0x4 #
VGBM VRF19,0x0
VLEIB VRF19,0xf0,15
VO VRF20,VRF20,VRF19
VPERM VRF16,VRF17,VRF20,VRF18
LHI R4,0x5
VSTL VRF16,R4,496(,R13) # TS2=119
VREPIB VRF20,0x40
LLC R4,2256(R2,R3) #
LTR R4,R4
JE L0642
AHI R4,0xffff
VSTL VRF20,R4,497(,R13) # TS2=119
L0642: EQU *
L R2,108(,R8) # BLL_9
MVC 8(5,R2),497(R13) # U016-CO-ID-DISPLAY TS2=119
I thought "All those vector instructions are better than an a single ED? I'd
better learn what that's doing so I can use that technique myself".
Today, I decided to recompile the module to see if it generates better code
since I noticed some of the above code could be further optimized. Our current
COBOL 6.4 compiler generated:
MVC 536(6,R13),2403(R3) # TS2=119 +2403
LLH R2,8(,R2) # U010-CO-ID
CVD R2,1050(,R13) #
ED 536(6,R13),1055(R13) # TS2=119
L R2,88(,R8) # BLL_9
MVC 8(5,R2),537(R13) # U016-CO-ID-DISPLAY TS2=119
Robert Ngan
DXC Luxoft
