Assembler Concepts Copyright 2008 by David Woolbright

Packed field must match the edit “word”

X’402020202120’ 5 digits

X’4020202021204B2020’ 7 digits

X’40202020’ 3 digits

Editing

• Create an edit word in memory that matches the packed field

• XWORD DC X’40202120’

• XPK DS PL2

• Move the edit word to the output area (must match the edit word)

• XOUT DS CL4
• MVC XOUT,XWORD

• Edit the packed field into the output area

• ED XOUT,XPK

Internal Subroutines

• BAS R7,SUB

• …

• BAS R7,SUB

• …

• SUB EQU *

• ___

• ___

• ___

• BR R7

Practice Exercise #2

• Greatest Common Divisor Computation for A and B

• Let rem = remainder of dividing the larger number by the smaller number

• Replace the larger number with rem

• Stop if A or B = 0, print A + B. Otherwise go to step 1

• Example A B

• 84 24

• 12 24

• 12 0 GCD = 12 + 0 = 12

Practice Exercise #2

• Create a file of records with two integers per record stored in a character format in columns 1-8

• Print each integer and the gcd. Print one record for each record in the input file

Practice Exercise #3

• Read a file that contains 3 5-byte fields in character format (cols 1-5,6-10, 11-15)

• Call the three fields A, B, C

• Assume A has 2 decimals, B has 3, and C has 4

• For each record in the file, print a record on a report

• Print A, B, C, A+B, (A+B)/C

• All answers should be good to one decimal rounded

• Don’t divide by 0

Binary Data

• Binary data is stored in 2’s complement format for signed arithmetic

• Binary data usually occurs as halfwords, fullwords, and doublewords

• Data can be defined as binary

• Data can be converted to binary from packed

• Some data is binary by nature (addresses)

You might need one of these

Defining Binary Data

• A DC F’1’

• B DC H’-30’

• C DC D’50’

• D DC B’10100000’

• E DC A(B)

• F DC X’0040’

Converting To Binary

Convert to Binary

• CVB

• RX

• Operand 1 – Register – target

• Operand 2 – Doubleword in memory – contains packed data

• Packed data is converted to binary and placed in the register

• Some doubleword values will not fit in a register

CVB Example

• XPK DC P’70’

• DBLWD DS D

• ZAP DBLDW,XPK

• CVB R8,DBLWD

• REG 8 = 00000046

Convert to Decimal

• CVD

• RX

• Operand 1 – Register - Source

• Operand 2 – Target is a Doubleword in memory – contains packed data afterward

• Binary data is converted to packed and placed in the doubleword

CVD Example

• ASSUME R9 = 00000032

• DBLWD DS D

• XPK DS PL3

• CVD R9,DBLWD

• ZAP XPK,DBLWD

• XPK = 00050C

Load and Store

• RX

• L – Loads a fullword from memory into a register

• ST – Copies the contents of a register into a fullword in memory

• Op 1 – a Register

• Op 2 – a fullword in memory

• X DS F’20’

• Y DS F

• L R8,X

• ST R4,Y

Load Register, Load and Test Register

• RR

• LR – Load Register

• LTR – Load and Test Register

• Both Load the contents of Op-2 into Op-1

• LTR sets the condition code

• Op-1 – a target register

• Op-2 – a source register

Types of RX Instructions

• Fullword Halfword Register

• L LH LR

• ST STH ---

• A AH AR

• S SH SR

• C CH CR

• M MH MR

• D --- DR

Add, Subtract, Compare Fullword

• RX

• A - Add Fullword

• S - Subtract Fullword

• C - Compare Fullword

• Operand 1 – Target Register

• Operand 2 – Fullword in memory (source)

•