Program Exceptions: Operation (if the decimal feature is not installed)
Access (fetch, operand 2; fetch and store, oper­
and 1)
Data
Decimal Overflow Programming Note
The operands of SUBTRACT DECIMAL may over­
lap when their low-order bytes coincide, even when
their lengths are unequal. This property may be used
to set to zero an entire field or the low-order part of
a field.
Zero and Add
ZAP
[
o
The second operand is placed in the first-operand
location.
The operation is equivalent to an addition to zero.
A zero result is positive. When high-order digits are
lost because of overflow, a zero result has the sign of
the second operand. Only the second operand is checked for valid sign
and digit codes. Extra high-order zeros are supplied
if needed. When the first-operand field is too short
to contain all significant digits of the second oper­
and, a decimal overflow occurs and results in a pro­
gram interruption, provided that the decimal over­
flow mask bit is one.
The first-operand and second-operand fields may
overlap :when the rightmost byte of the first-operand
field is coincident with or to the right of the right­
most byte of the second operand. In this case the
result is obtained as if the operands were processed
right to left.
Resulting Condition Code:
o Result is zero
1 Result is less than zero
2 Result is greater than zero
3 Overflow Program Exceptions: Operation (if the decimal feature is not installed)
Access (fetch, operand 2; store, operand 1)
Data
Decimal Overflow Decimal Instructions 155
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