 DP is a SS2 instruction which is used to divide two packed decimal fields and produce a quotient and a remainder.  Since packed decimal fields are integers, the division that occurrs is an integer division.  If you are interested in producing a quotient with decimals, you may need to  use SRP to shift the quotient before the division, and ED to provide a decimal point in the output.  (See the topic on “Decimal Precision”.)

Operand 1 is a field containing a packed decimal number which is the dividend.  Both the quotient and the remainder develop in this field.  Operand 2 is a packed decimal field containing the divisor.  The maximum length of the dividend is 16 bytes, and the maximum length of the divisor is 8 bytes.  Keep in mind the following rules when thinking about the sizes of the generated quotient and remainder,

1)  The remainder size is equal to the size of the divisor.

2)  The quotient occupies the portion of operand 1 that is not occupied by the remainder.

The rules make practical sense when you think about the division process.  Suppose you divide an m-byte divisor into an n-byte dividend.  Without knowing the specific values, we can see that in an integer division, the remainder might be as large as m bytes, and the quotient might be as large as n-bytes.  This observation leads to the following rule of thumb for creating work fields in which to perform the calculation,

If the dividend is an n-byte field, and the divisor is an m-byte field, make the work field for the computation at least n+m bytes.

Following this rule of thumb will insure that the dividend contains a sufficient number of bytes of leading zeroes before the computation.  Specifically, the number of bytes of leading zeroes in the dividend must be at least large as the number of bytes in the divisor.  Here is a sample computation where we want to divide APK by BPK.  Since APK is 3 bytes and BPK is 2 bytes, we create a work area called “WORK” which is 5 bytes.  This will provide the required number of bytes of leading 0’s for our computation. DP does not set the condition code. Some unrelated DP’s:

LPK      DC      PL4’100’      = X’0000100C’

MPK      DC      PL3’6’        = X’00006C’

NPK      DC      PL2’6’        = X’006C’

OZONE    DC      Z’11’         = X’F1C1’

WORK1    DS     0CL7

QUOT1    DS      PL4

REM1     DS      PL3

WORK2    DS     0CL7

QUOT2    DS      PL5

REM2     DS      PL2

...

Results:

ZAP   WORK1,LPK   WORK = X’0000000000100C’

DP    WORK1,MPK   WORK = X’0000016C00004C  QUOT1=16, REM1=4

LENGTH OF REM1=3

ZAP   WORK2,LPK   WORK = X’0000000000100C’

DP    WORK2,NPK   WORK = X’000000016C004C  QUOT1=16, REM1=4

LENGTH OF REM2=2

ZAP   WORK1,LPK   WORK = X’0000000000100C’

DP    WORK1,OZONE  ABEND - OZONE NOT PACKED

ZAP   WORK1,=P’1234567890’  WORK = X’0001234567890C’

DP    WORK,MPK       ABEND - NOT ENOUGH BYTES OF LEADING 0’S

IN WORK1 - NEEDS 3 BYTES 1.  Don’t divide by zero.  An attempt to divide by zero causes an “0CB” abend.  Protect your divisions by testing the divisor before you divide.

ZAP    BPK,BPK      IS DIVISOR 0?

BZ     ZERODIV      BRANCH IF ZERO

ZAP    WORK,APK     OTHERWISE...

DP     WORK,BPK     ... WE CAN DIVIDE

...

ZERODIV  EQU    *

(CODE TO HANDLE A ZERO DIVISOR)