CSC233 Assembly Language - Packed Decimal Arithmetic

Packed Decimal Arithmetic

Add Packed Instruction (AP)

The AP instruction is an SS instruction that adds two packed decimal fields. The result of the addition is stored in the first operand. The two operands are added byte by byte, starting at the low-order byte.

Rules for the AP instruction:

The length of each operand can either be implicit or explicit, as in the PACK instruction.
The maximum length for either operand is 16 bytes.
Operand 2 can be a self-defining operand of type P.
If either operand has a sign of F, the AP instruction will change the sign to C.
Be careful when using an explicit length; if used incorrectly, the low order byte may not contain a valid sign.
If the first operand is not large enough to hold the result, the high order digit(s) will be truncated.
If either operand does not contain a valid packed decimal number, a data exception interrupt will occur and the program will be terminated.

Examples

Given the following definitions:

ONE      DC     PL3'11223'
TWO      DC     PL3'1950'
THREE    DC     P'256'
FOUR     DC     C'999'
FIVE     DC     C'123 '
SIX      DS     PL3
SEVEN    DC     PL2'-300'

	Before		After
AP Instruction	Operand 1	Operand 2	Operand 1	Operand 2
AP ONE,TWO	11 22 3C	01 95 0C	13 17 3C	01 95 0C
AP ONE(3),THREE(2)	11 22 3C	25 6C	11 47 9C	25 6C
AP ONE(3),THREE(1)	11 22 3C	25	data exception, op2 invalid
AP THREE,TWO	25 6C	01 95 0C	20 6C	01 95 0C
AP ONE,FOUR	11 22 3C	F9 F9 F9	data exception, op2 invalid
PACK SIX,FIVE AP SIX,TWO	01 23 04	01 95 0C	data exception, op1 invalid
AP THREE,SEVEN	25 6C	30 0D	04 4D	30 0D
AP THREE,=P'128'	25 6C	12 8C	38 4C	12 8C

Subtract Packed Instruction (SP)

The SP instruction is an SS instruction that subtracts two packed decimal fields. The second operand is subtracted from the first operand, and the result of the subtraction is stored in the first operand, that is, op1 is set to the result of op1 - op2. When subtracting signed numbers, remember that the rules for subtraction can be summarized by "change the sign of the second operand, and then add."

Rules for the SP instruction:

The length of each operand can either be implicit or explicit.
The maximum length for either operand is 16 bytes.
Operand 2 can be a self-defining operand of type P.
If either operand has a sign of F, the SP instruction will change the sign to C.
Be careful when using an explicit length; if used incorrectly, the low order byte may not contain a valid sign.
If the first operand is not large enough to hold the result, the high order digit(s) will be truncated.
If either operand does not contain a valid packed decimal number, a data exception interrupt will occur and the program will be terminated.

Examples

Given the following definitions:

ONE      DC     PL3'12500'
TWO      DC     PL3'1750'
THREE    DC     P'-250'
FOUR     DC     P'-1000'

	Before		After
SP Instruction	Operand 1	Operand 2	Operand 1	Operand 2
SP ONE,TWO	12 50 0C	01 75 0C	10 75 0C	01 75 0C
SP TWO,THREE	01 75 0C	25 0D	02 00 0C	25 0D
SP FOUR,TWO	01 00 0D	01 75 0C	02 75 0D	01 75 0C
SP FOUR,THREE	01 00 0D	25 0D	00 75 0D	25 0D
SP THREE,TWO	25 0D	01 75 0C	00 0D	01 75 0C
SP ONE,=P'500'	12 50 0C	50 0C	12 00 0C	50 0C
SP ONE(2),TWO	12 50	01 75 0C	data exception, op1 invalid