The easy one is the LPD/MVCOS comparison. It has more to do with the function of the instruction than the format of the instruction.
LPD, or LOAD PAIR DISJOINT, if you think about it and say it in English is LOAD a register pair from location A and location B MVCOS said in English is Move to location A from location B for a length in the register These are consistent with other LOAD or MOVE instructions, so I think their goal was consistency in the format of the function, rather than consistency with the instruction hardware format. I don't have any personal knowledge about this, but as an outsider, that is my take on it. Chris Blaicher Principal Software Engineer, Software Development Syncsort Incorporated 50 Tice Boulevard, Woodcliff Lake, NJ 07677 P: 201-930-8260 | M: 512-627-3803 E: [email protected] -----Original Message----- From: IBM Mainframe Assembler List [mailto:[email protected]] On Behalf Of Farley, Peter x23353 Sent: Thursday, March 26, 2015 4:45 PM To: MVS List Server 2 Subject: HLASM operand order vs. instruction operand order I guess this question is mostly for John Ehrman, but others may have insight as well. For the same machine instruction format, there are sometimes two different HLASM operand orders used for the operands of instructions. For example, LOC has HLASM operands in order 1,2,3 while STMCH operands are in order 1,3,2 and the machine instruction operands are in order 1,3,2: LOC R1,D2(B2),M3 [RSY-b] 'EB' R1 M3 B2 DL2 DH2 'F2' 0 8 12 16 20 32 40 47 STCMH R1,M3,D2(B2) [RSY-b] 'EB' R1 M3 B2 DL2 DH2 '2D' 0 8 12 16 20 32 40 47 Here is a second example, LPD has HLASM order 3,1,2 while MVCOS has HLASM order 1,2,3 and the machine operands are in order 3,1,2: LPD R3,D1(B1),D2(B2) [SSF] 'C8' R3 '4' B1 D1 B2 D2 0 8 12 16 20 32 36 47 MVCOS D1(B1),D2(B2),R3 [SSF] 'C8' R3 '0' B1 D1 B2 D2 0 8 12 16 20 32 36 47 Am I the only one to whom the inconsistency seems arbitrary? Or am I missing some salient characteristic that explains the differences? Peter -- This message and any attachments are intended only for the use of the addressee and may contain information that is privileged and confidential. If the reader of the message is not the intended recipient or an authorized representative of the intended recipient, you are hereby notified that any dissemination of this communication is strictly prohibited. If you have received this communication in error, please notify us immediately by e-mail and delete the message and any attachments from your system.
