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Definitions |
Packed decimal | specifies a method of encoding decimal
numbers by using each byte to represent two decimal digits. Packed decimal
representation stores decimal data with exact precision. The fractional part
of the number is determined by the informat or format because there is no
separate mantissa and exponent.
An advantage of using packed decimal data is that exact precision can be maintained. However, computations involving decimal data may become inexact due to the lack of native instructions. |
Zoned decimal | specifies a method of encoding decimal numbers in which each digit requires one byte of storage. The last byte contains the number's sign as well as the last digit. Zoned decimal data produces a printable representation. |
Nibble | specifies 1/2 of a byte. |
Types of Data |
The sign indication is dependent on your operating environment. On IBM mainframes, the sign is indicated by the last nibble. With formats, C indicates a positive value, and D indicates a negative value. With informats, A, C, E, and F indicate positive values, and B and D indicate negative values. Any other nibble is invalid for signed packed decimal data. In all other operating environments, the sign is indicated in its own byte. If the high-order bit is 1, then the number is negative. Otherwise, it is positive.
The following applies to packed decimal data representation:
The following applies to zoned decimal data representation:
The following applies to packed Julian dates:
Platforms Supporting Packed Decimal and Zoned Decimal Data |
Languages Supporting Packed Decimal and Zoned Decimal Data |
IBM VS COBOL II clauses | Corresponding S370Fxxx formats/informats |
---|---|
PIC S9(X) PACKED-DECIMAL | S370FPDw. |
PIC 9(X) PACKED-DECIMAL | S370FPDUw. |
PIC S9(W) DISPLAY | S370FZDw. |
PIC 9(W) DISPLAY | S370FZDUw. |
PIC S9(W) DISPLAY SIGN LEADING | S370FZDLw. |
PIC S9(W) DISPLAY SIGN LEADING SEPARATE | S370FZDSw. |
PIC S9(W) DISPLAY SIGN TRAILING SEPARATE | S370FZDTw. |
For the packed decimal representation listed
above,
X indicates the number of digits represented, and W is the number of bytes.
For PIC S9(X) PACKED-DECIMAL, W is
ceil((x+1)/2)
. For PIC 9(X) PACKED-DECIMAL, W is
ceil (x/2)
. For example, PIC S9(5) PACKED-DECIMAL
represents five digits. If a sign is included, six nibbles are needed.
ceil((5+1)/2)
has a length of
three bytes, and the value of W is 3.
Note that you can substitute COMP-3 for PACKED-DECIMAL.
In IBM assembly language, the P directive indicates packed decimal, and the Z directive indicates zoned decimal. The following shows an excerpt from an assembly language listing, showing the offset, the value, and the DC statement:
offset value (in hex) inst label directive +000000 00001C 2 PEX1 DC PL3'1' +000003 00001D 3 PEX2 DC PL3'-1' +000006 F0F0C1 4 ZEX1 DC ZL3'1' +000009 F0F0D1 5 ZEX2 DC ZL3'1'
In PL/I, the FIXED DECIMAL attribute is used in conjunction with packed decimal data. You must use the PICTURE specification to represent zoned decimal data. There is no standardized representation of decimal data for the FORTRAN or the C languages.
Summary of Packed Decimal and Zoned Decimal Formats and Informats |
Format | Type of data representation | Corresponding informat | Comments |
---|---|---|---|
PD | Packed decimal | PD | Local signed packed decimal |
PK | Packed decimal | PK | Unsigned packed decimal; not specific to your operating environment |
ZD | Zoned decimal | ZD | Local zoned decimal |
none | Zoned decimal | ZDB | Translates EBCDIC blank (hex 40) to EBCDIC zero (hex F0), then corresponds to the informat as zoned decimal |
none | Zoned decimal | ZDV | Non-IBM zoned decimal representation |
S370FPD | Packed decimal | S370FPD | Last nibble C (positive) or D (negative) |
S370FPDU | Packed decimal | S370FPDU | Last nibble always F (positive) |
S370FZD | Zoned decimal | S370FZD | Last byte contains sign in upper nibble: C (positive) or D (negative) |
S370FZDU | Zoned decimal | S370FZDU | Unsigned; sign nibble always F |
S370FZDL | Zoned decimal | S370FZDL | Sign nibble in first byte in informat; separate leading sign byte of hex C0 (positive) or D0 (negative) in format |
S370FZDS | Zoned decimal | S370FZDS | Leading sign of - (hex 60) or + (hex 4E) |
S370FZDT | Zoned decimal | S370FZDT | Trailing sign of - (hex 60) or + (hex 4E) |
PDJULI | Packed decimal | PDJULI | Julian date in packed representation - IBM computation |
PDJULG | Packed decimal | PDJULG | Julian date in packed representation - Gregorian computation |
none | Packed decimal | RMFDUR | Input layout is: mmsstttF |
none | Packed decimal | SHRSTAMP | Input layout is: yyyydddFhhmmssth, where yyyydddF is the packed Julian date; yyyy is a 0-based year from 1900 |
none | Packed decimal | SMFSTAMP | Input layout is: xxxxxxxxyyyydddF, where yyyydddF is the packed Julian date; yyyy is a 0-based year from 1900 |
none | Packed decimal | PDTIME | Input layout is: 0hhmmssF |
none | Packed decimal | RMFSTAMP | Input layout is: 0hhmmssFyyyydddF, where yyyydddF is the packed Julian date; yyyy is a 0-based year from 1900 |
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