Signed overpunch
A signed overpunch is a code used to store the sign of a number by changing the last digit. It is used in character data on IBM mainframes by languages such as COBOL, PL/I, and RPG.[1] Its purpose is to save a character that would otherwise be used by the sign digit.[2] The code is derived from the Hollerith Punched Card Code, where both a digit and a sign can be entered in the same card column. Character data which may contain overpunches is called zoned decimal.
The PACK instruction on IBM System/360 architecture machines converts the sign of a zoned decimal number when converting to packed decimal,
and the corresponding UNPK instruction will set the correct overpunched sign of its zoned decimal output.[3]
Language support
PL/I
PL/I uses the PICTURE attribute to declare zoned decimal data with a signed overpunch. Each character in a numeric picture except V, which indicates the position of the assumed decimal point, represents a digit. A picture character of T, I, or R indicates a digit position which may contain an overpunch. T indicates that the position will contain {–I if positive and }–R if negative. I indicates that the position will contain {–I if positive and 0-9 if negative. R indicates that the position will contain 0–9 if positive and }–R if negative.
For example PICTURE 'Z99R' describes a four-character numeric field. The first position may be blank or will contain a digit 0–9. The next two positions will contain digits, and the fourth position will contain 0–9 for a positive number and }–R for negative.[4]
Assigning the value 1021 to the above picture will store the characters "1021" in memory; assigning -1021 will store "102J".
The codes
| Code | Digit | Sign |
|---|---|---|
| } | 0 | − |
| J | 1 | − |
| K | 2 | − |
| L | 3 | − |
| M | 4 | − |
| N | 5 | − |
| O | 6 | − |
| P | 7 | − |
| Q | 8 | − |
| R | 9 | − |
| { | 0 | + |
| A | 1 | + |
| B | 2 | + |
| C | 3 | + |
| D | 4 | + |
| E | 5 | + |
| F | 6 | + |
| G | 7 | + |
| H | 8 | + |
| I | 9 | + |
Examples
10} is -100
45A is 451
Decimal points are usually implied and not explicitly stated in the text. Using numbers with two decimal digits:
1000} is -100.00
References
- ↑ IBM Corporation (June 1994). RPG/400 Reference (PDF). p. 403. Retrieved Aug 7, 2018.
- ↑ "Tech Talk, COBOL Tutorials, EBCDIC to ASCII Conversion of Signed Fields". Retrieved 2008-03-15.
- ↑ IBM Corporation (Oct 2001). z/Architecture Principles of Operation (2nd ed.). pp. 7–112, 7–158. Retrieved August 7, 2018.
- ↑ IBM Corporation (June 1995). IBM PL/I for MVS & VM Language Reference (PDF). pp. 294–296. Retrieved Aug 2, 2018.