Wirt - 

Interestig mnemonic for the sign nibbles.  Hadn't heard it described that
way before.

I feel certain that the choice of x'C' and x'D' as sign characters has its
roots in the way signed zoned numbers are stored.  And the method we use for
storing signed zoned numbers has its roots in Hollerith card codes (punch
cards).  Numbers punched on Hollerith cards were signed by overpunching the
last digit with either a '+' (zone 12) or a '-' (zone 11) punch giving us
the possibly familiar ( {, A, B, ..., I and }, J, K, ..., S ) sign
characters.  The EBCDIC values for those character ranges start with x'C'
and x'D' respectively. Creating hardware to pack and unpack numbers while
retaining the sign was made relatively easy by simply using the last
high-order nibble (whatever it was) as the sign.

Regards.

Glenn
-----Original Message-----
From: HP-3000 Systems Discussion [mailto:[log in to unmask]] On Behalf
Of Wirt Atmar
Sent: Friday, November 25, 2005 2:41 PM
To: [log in to unmask]
Subject: Re: [HP3000-L] Packed Fields

...

I would expect that the data is packed in the standard manner: each nibble
(4
bits) in the pattern is a binary encoded decimal ranging from 0 ("0000") to
9 ("1001"), except for the last nibble, which is the sign of the number. If
no sign value is specified, the last nibble is the hex value"F" ("1111"). 
Otherwise, it's a "C" (credit; "1100") for a positive value, "D" (debit;
"1101") for a negative value.

Wirt Atmar

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