COBOL allows definitions of decimal numeric fields to be signed or
unsigned packed decimal or external decimal (as well as other other
formats).
I believe it had always generated Compared Packed hardware instructions
to compare signed decimal fields, ensuring that negative and positive
were properly collated. But this is relatively slow.
For speed more recent compilers could generate the faster CLC
instructions for unsigned decimal fields. However problems arise when
the data in the unsigned field came from an external source and unsigned
fields did not consistently use the C or the F nybble for the sign.
One practical effect of the F-zone or C-zone in a signed number is the
COBOL DISPLAY command, which uses the hardware Unpack instruction to
convert the number to EBCDIC but does not interpret the sign. The last
digit displayed will be numeric if an F-zone, but alphabetic if a
C-zone. For other zones, it could be alphabetic or weird.
On 2025-04-29 12:00 a.m., IBM-MAIN automatic digest system wrote:
Date: Tue, 29 Apr 2025 09:40:09 +1000
From: Andrew Rowley<[email protected]>
Subject: Re: Packed decimal sign nibbles
On 29/04/2025 9:32 am, Seymour J Metz wrote:
The decimal instructions treat F zones as positive.
That's always been my understanding. But I'm intrigued by the statement
that it means unsigned in COBOL. Is there a practical difference? Or is
it just a difference e.g. for formatting output?
Gary Weinhold
Senior Application Architect
DATAKINETICS | Data Performance & Optimization
Phone:+1.613.523.5500 x216
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