RPG II

From MidrangeWiki
Jump to: navigation, search

RPG II is a version of the RPG programming language. It was developed in the late 1960s and was offered on a number of different computers, including the IBM System/3, System/32, System/34, System/36, System/370 and the Wang VSSeries.

RPG stands for Report Program Generator. RPG is a fixed-format programming language, which means that code must be placed in exact column locations in order to generate correct results. COBOL and BASIC are considered free-format to some extent because the code can be placed variously and still generate correct results.

RPG also incorporates fixed logic, which means that files are opened when the program begins and closed when the program ends, even though this is not explicitly stated; special variables such as UDATE, UYEAR, PAGE, and so forth, are filled when the program begins or when page overflow occurs, even though there is no explicit instruction for these activities. Total calculations and output are done at "total time," after the detail cycle when L1/LR has been set on by fixed logic.

The concept of RPG fitted neatly with a cyclical machine that read cards, summarised their contents and prints a result, rather like a tabulating machine. The language was extended to handle other input and output devices and provides a fast and efficient method of programming.

Devices such as the workstation (WORKSTN), the keyboard (KEYBORD), or the console (CONSOLE) do not have a fixed number of records at the beginning of the job and therefore, in order to incorporate the fixed-logic RPG "Last Record" cycle, the LR indicator can be set on with a SETON instruction. LR cannot be set off.

While RPG II itself did not evolve much from the 1977 implementation on the System/34 to 2000 when the Advanced/36 was discontinued from marketing, third-party providers sold more than 200 different assembler subroutines that could be used by System/36 and Advanced/36 programmers to exceed RPG II limitations. By using RPG subroutines, programmers could close and re-open printer files, directly access devices, library members, and system areas, and perform true program calls. The "keys to the kingdom" of advanced RPG II programming are contained in these subroutines.

Contents

RPGII Specifications

 In the popular System/36 implementation of RPG II, there are 8 different specification
 types:
 
 (1) The U or Auto Report spec is only required for Auto Report programs.
 
 (2) The H or Header spec is at the top of the program and describes compiler options such as
 maximum compile size, whether the program is a MRT or Multiple Requestor Terminal program,
 and what type of listing is generated when the program is compiled.  The object name of the
 program created is located in columns 75-80;if a source does not have an H spec, the name
 RPGOBJ is used.
 
 (3) The F or File spec(s) are next, and describes the files used in the program.  Files may be
 disk files (DISK) or may be devices such as a printer (PRINTER), the workstation (WORKSTN),
 keyboard (KEYBORD), unformatted display (CRT or DISPLAY), or user-defined (SPECIAL).  Record
 size, block size, overflow indicators, and external indicators are described.  It is possible
 that an RPG program will not use any F specs.
 
 (4) The E or Extension spec(s) are next, and describe arrays and tables, which may be
 prefetched from disk files (an Input table), drawn from constants placed at the end of the
 source between ** and /* symbols, or built from calculations.
 
 (5) The L or Line Counter spec(s) are next, and if present, describe the form to be printed.
 It defines the number of lines in a page and the positions where printing begins and ends.
 
 (6) The I or Input specs are next, and describe the data areas within files.  RPG II permits
 redefinition of data areas so that a field named FLDA might occupy the same area as an array
 AR that contains 8 elements of 1 character each.  Non-record areas such as data structures can
 be described.  Depending on the values of the input record, indicators may be conditioned.
 
 (7) The C or Calculation spec(s) are next.  Total fields may be described and accumulated.
 Complex computations and string manipulations are possible.  Indicators may be conditioned.
 
 (8) The last specification(s) are O or Output specifications, which describe the output record
 in terms of fields and output positions.
 
 
 OPERATION CODES appear in columns 28-32 of an RPG-II calculation specification.
 
 ADD     Add
 SUB     Subtract
 MULT    Multiply
 DIV     Divide
 Z-ADD   Zero and Add
 Z-SUB   Zero and Subtract
 MVR     Move Remainder 
  
 MOVE    Move
 MOVEL   Move Left
 
 MHLZO   Move High to Low Zone
 MLHZO   Move Low to High Zone
 MLLZO   Move Low to Low Zone
 MHHZO   Move High to High Zone
 
 BITON   Bit On
 BITOF   Bit Off
 TESTB   Test Bit
 
 GOTO    Go To
 TAG     Tag (Object of a GOTO)
 EXSR    Execute Subroutine
 BEGSR   Begin Subroutine
 ENDSR   End Subroutine
 
 SETON   Set On
 SETOF   Set Off
 
 EXCPT   Exception
 
 EXIT    Exit
 RLABL   Redefine Label
 ULABL   User Label
 
 CALL(*) Call
 PARM(*) Parameter
 
 CHAIN   Chain
 READ    Read
 READE   Read Equal
 READP   Read Previous
 REDPE   Read Previous Equal
 SETLL   Set Lower Limits
 
 SET     Set
 TIME    Time of day (000000-235959)
 DSPLY   Display
 SORTA   Sort Array
 XFOOT   Crossfoot
 MOVEA   Move Array
 LOKUP   Lookup (find in array)
 
  • CALL/PARM was added to RPG II with Release 6.0 (also known as the VASP.)

CHAIN retrieves the record in the indexed file named in Factor 2 that matches the exact key specified by the value in Factor 1.

SETLL causes the index pointer for the file named in Factor 2 to be positioned at the location specified by the value in Factor 1.

SORTA causes the named array to be sorted in place; that is, the elements appear in order.

Z-SUB calculates Factor 2 with opposite sign and moved to result field.

XFOOT causes an array to be summed and the result moved to result field.

MVR must follow a DIV operation. The integer remainder of the DIV operation is placed in the result field. MVR following the DIV operation for "56 divided by 3" would place the value 2 in the result field.

I N D I C A T O R S

 Standard
 
 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90
 91 92 93 94 95 96 97 98 99
 
 
 Halt Indicators
 
 H1 H2 H3 H4 H5 H6 H7 H8 H9
 
 
 Matching Indicators
 
 M1 M2 M3 M4 M5 M6 M7 M8 M9 MR
 
 
 Control-Level Indicators
 
 L1 L2 L3 L4 L5 L6 L7 L8 L9
 
 
 Command Key Indicators
 
 KA KB KC KD KE KF KG KH KI KJ KK KL KM KN KP KQ KR KS KT KU KV KW KX KY
 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
 
   (These indicators refer to command keys 1 to 24.  Note there is no "KO" indicator.)
 
 
 First Cycle Indicator
 
 1P
   
 Last Record Indicator
 
 LR
 
 
 Overflow Indicators
 
 OA OB OC OD OE OF OG OV
 
 
 External Indicators
 
 U1 U2 U3 U4 U5 U6 U7 U8
 System/36 SEU templates
 
 3=H
 5=F/files
 6=F/extensions
 7=E
 8=L
 10=I/header
 11=I/fields
 12=C
 13=O/header
 14=O/fields

See Also

IBM System/34 IBM System/36 IBM Advanced/36 IBM AS/400


External links

Categories