If
no
indirect
addressing
or
indexing is used with DSA, the
shift
count
C
is
the confents
of
bit
positions 16-31
of
the
instruction word.
If
on
Iy
indirect
addressing
is
used
with
DSA, the shift
count
is
the contents
of
bit
positions 16-31
of
the word pointed to by the
indirect
address in
the
in-
struction word. If indexing only
is
used with DSA, the
shift
count
is the
contents
of
bit
positions 16-31
of
the
instruction word plus
the
contents
of
bit
positions
14-29
of
the
designated
index
register
(bits
0-13,
30,
and
31
of
the
index
are
ignored).
If
indirect
addressing
and
indexing
are
both used with DSA,
the
shift
count
is
the
sum
of
the
contents
of
bit
positions 16-31
of
the word
pointed
to by
the
indirect
address and the contents of
bit
positions
14-29
of
the
designated
index
register.
The shift
count,
C,
is
treated
as a
16-bit
signed
binary
integer,
with
negative
integers in two·s complement form.
If the shift
count
is
positive,
the
contents
of
the
decimal
accumulator
are
shifted
left
C decimal
digit
positions;
if
the shift
count
is
negative,
the
contents
of
the
decimal
accumulator
are
shifted right
-C
decimal
digit
positions.
In
either
case,
the
decimal
sign is
not
shifted,
vacated
decimal
digit
positions
are
fi lied
with
O·s, and
any
digits
shifted
out
of
the
decimal
accumulator
are
lost. Although
the
range
of
possible
values
for C is
2-
15
$ C $
215-1.
a shift
count
greater
than
+31
or
less than -31
is
interpreted
as a shift
count
of
exactly
+31
or
-31.
If
any
nonzero decimal
digit
is shifted
out
of
the
decimal
accumulator
during a
left
shift, CC2
is
set
to
1;
otherwise,
CC2
is
reset
to
O.
CC2
is
unconditionally
reset
to 0
at
the
•
completion
of
a right shift.
Affected:
(DECA), CC
Trap: Decimal
arithmetic
Condition
code
settings:
2 3 4 Result in
DECA
o Illegal
digit
or sign
detected,
instruction
aborted
o - 0 0 Zero
o - 0
Negative
o - 0 Positive
o 0 Right shift
or
no
non-
zero
digit
shifted
out
of
DECA
on
left
shift
o
One
or
more
nonzero
digit(s) shifted
out
of
DECA
on
left
shift
No
illegal
digit
or
sign
detected,
i nstructi on
completed
PACK
PACK DECIMAL DIGITS
(Byte
index
alignment)
PACK DECIMAL DIGITS converts
the
effective
decimal
operand
(assumed to be in
zoned
format) into a
packed
decimal number
and,
if
necessary, appends
sufficient
high-
order
O·s
to produce a decimal number
that
is 16 bytes
(31
decimal
digits plus sign) in length.
The
zone
(bits
0-3)
of
the
low-order
digit
of
the
effective
deci mal operand is
used to
select
the sign
code
for the
packed
decimal
number;
all
other
zones
are
ignored in formatting the
packed
decimal
number. If no i
/legal
digit
or
sign
appears
in the
packed
decimal
number,
it
is then loaded
into
the
decimal
accu-
mulator.
If
the result in the decimal
accumulator
is
zero,
the resulting sign remains
unchanged.
The L
field
of
this instruction
specifies
the
length, in bytes,
of
the
resultant
packed
decimal
number in
the
decimal
ac-
cumulator;
therefore,
the length
of
the
effective
decimal
operand is 2L-1 bytes (where L = 0 implies a length
of
31
bytes for
the
effecti
ve
deci
ma
I
operand).
Affected:
(DECA), CC
Trap: Decimal
arithmetic
packed
(EBL
to
EBL
+
2L
- 2)
-DECA
Condition
code
settings:
2 3 4 Result in
DECA
o - -
Illegal
digit
or
sign
detected,
instruction
aborted
o 0 0 0 Zero
No
i /legal
digit
or
sign
0 0 0
Negative
detected,
instruction
completed
0 0
0
Positive
Example 1,
L
=
6:
Before
execution
After
execution
EDO X·FOF1F2F3 X·FOF1F2F3
F4F5F6F7
F4F5F6F7
F8F9FO· F8F9FO·
(DECA)
xxxxxxxx
X·OOOOOOOO
xxxxxxxx
00000000
xxxxxxxx 00000123
xxxxxxxx
4567890C·
CC
xxxx 0010
Decimal Instructions
85
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