Subtract Decimal
(SP)
General Description
Format
(55)
Condition Code
Interrupt
Action
Notes
Decimal Arithmetic
Instructions
• The operand specified by
the
second address (B
2
/D
2
)
is subtracted
algebraically
from
the
operand specified by the first address (B1/D
1
).
The
result is stored in the field specified by the first address. The sign
and
the
magnitude
of
the
difference determine
the
condition code.
The operands can
be variable
in
length up
to
16 bytes
and
must
be in
packed format.
If
operands overlap,
their
rightmost
byte
location
must
coincide.
The
subtraction
of
two operands can cause decimal overflow.
FB
o
7 8
11
12
15
16
19
20
31
32
35 36
47
• 0 - difference is zero.
1-
difference is less
than
zero.
2 - difference is
greater
than
zero.
3-
overflow.
• Address
error:
Addressing.
Protection.
Data
error.
Decimal overflow.
• 1. High-order zeros
are
supplied
for
either operand
during
instruction
execution.
2. All signs
and
digits
are
checked
for
validity.
3. The operand specified by
the
second address is unaltered.
4. Processing is
from
right
to left.
5. A zero difference is always positive except when high-order digits
are
lost because
of
overflow.
In
overflow, a zero result
has
the
sign
of
the
correct difference.
159
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