Assembler Concepts Copyright 2008 by David Woolbright

RECFM=(FB)

• The record format
• FB – fixed blocked
• VB – variable blocked
• F – fixed unblocked
• V – variable unblocked

EODAD=label

• End of Data Address. Branch here when EOF.

LRECL=length

• Logical Record Length. Take default blocksize.

Opening and Closing Files

• OPEN (FILEIN,(INPUT)) THE INPUT FILE

• OPEN (FILEOUT,(OUTPUT)) MY REPORT

• ... (process the files)

• CLOSE FILEIN

• CLOSE FILEOUT

Reading and Writing Records

• * MOVE MODE IO

• GET FILEIN,RECIN

• WSPC1 EQU X’09’

• MVI RECOUT,WSPC1

• MVC MESSAGEO,MESSAGEI

• PUT FILEOUT,RECOUT

Standard Entry and Exit

• SKELAD4 CSECT

• * STANDARD ENTRY

• STM R14,R12,12(R13) STANDARD ENTRY

• BASR R12,R0

• USING *,R12

• ST R13,SAVE+4

• LA R13,SAVE

• L R13,SAVE+4

• …

• * STANDARD EXIT

• LM R14,R12,12(R13)

• LA R15,0

• BR R14

Save Area (18F)

Practice Exercise #1

• Create a PDS member with dates in the following format:

• YYYYMMDD (columns 1-8)

• One date per record. Assume valid data.

• Print Three records for each input record read.

• Reformat the data in the following format:

• Year: 2004

• Month: January

• Day: 23

Packed Decimal Data

• Two decimal digits per byte

• Sign occurs in the numeric portion of the rightmost byte

• Valid signs: A,C,F are +

• B, D are -

• Preferred signs: C (+), D (-)

• XPK DC PL3’54’

• Generates: 00054C

Example Packed Data Fields

• APK DC P’12345’ 12345C

• BPK DC PL2’12345’ 345C

• CPK DC PL4’123.45’ 0012345C

• DPK DC P’-345’ 345D

• EPK DC P’0’ 0C

• FPK DC P’-1’ 1D

Zoned Decimal Data

• One decimal digit per byte

• Sign occurs in the zone portion of the rightmost byte

• Valid signs: A,C,F are +

• B, D are -

• Preferred signs: C (+), D (-)

• XPK DC ZL5’-354’

• Generates: F0F0F3F5D4

• Some character fields qualify as zoned:

• X DC C’12345’

• Generates: F1F2F3F4F5

Example Zoned Data Fields

• AZD DC Z’12345’ F1F2F3F4C5

• BZD DC ZL2’-12345’ F4D5

• CZD DC Z’-12345’ F1F2F3F4D5

• DZD DC ZL4’-345’ F0F3F4D5

• EZD DC Z’0’ C0

• FZD DC Z’-1’ D1

• GC DC C’12345’ F1F2F3F4F5

Packed Instructions - Pack

• SS2

• The PACK instruction converts from zoned decimal to packed decimal

• XZD DC Z’-1234’ F1F2F3D4

• XPK DS PL4 0001234D

• …

• PACK XPK,XZD

Packed Instructions - Pack

• The receiving field can be too short

• XZD DC Z’-12345’ F1F2F3F4D5

• XPK DS PL2 345D

• …

• PACK XPK,XZD

• Any data can be packed – results not always good

Packed Decimal Arithmetic Issues

• Each operand contains at most 16 bytes – 31 digits plus a sign

• Data Exceptions occur when performing arithmetic on data that is not packed

• Loss of precision can occur on ZAP, AP, SP – no notification

Packed Arithmetic - ZAP

• SS2

• Use ZAP to move packed data (not MVC)

• XPK DS PL4

• YPK DC P’54’ 054C

• ZAP XPK,YPK

• MVC XPK,YPK WHY NOT?

• Final result in XPK: 0000054C

• Sets the condition code to Positive, Minus, or equal

• Test with BP, BM, BE, BNP, BNM, BNE

Packed Arithmetic - AP

• SS2 – Add packed

• Op1 – Target Field (max 16 bytes)

• Op2 – Source Field (max 16 bytes)

• The target contains the arithmetic sum of Op1 and Op2

• Sets the condition code:

• High – result > 0 Test with BP, BNP
• Low – result < 0 Test with BM, BNM
• Equal – result = 0 Test with BZ, BNZ

Packed Arithmetic - SP

• SS2 – Subtract packed

• Op1 – Target Field (max 16 bytes)

• Op2 – Source Field (max 16 bytes)

• The target contains the arithmetic result of subtracting Op2 from Op1

•