Page 222 - Introduction to Microcontrollers Architecture, Programming, and Interfacing of The Motorola 68HC12

7.4 Long Integer Arithmetic 199

* SUBROUTINE MULT multiplies the unsigned next word on the stack with
* L, and pulls the next word
sK
LCSAVE: EQU *
ORG 0
PROD: DS.L 1
N: DS.L 1
M: DS.L 1

ORG LCSAVE
MULT: PULX ; pull return address
PSHD ; low part of N
PSHY ; high part of N
*
LDY M+2 - 4, SP ; note: M is operand offset in sub middle
EMUL ; note - accum D is still low part of N
PSHD ; low word of product
PSHY ; high word of product
*
LDD N, SP ; get high part of N
LDY M+2, SP ; get low part of M
EMUL
ADDD PROD, SP ; add to high word
STD PROD r SP ; place back
*
LDD N+2, SP ; get low part of N
LDY M, SP ; get high part of M
EMUL
ADDD PROD, SP ; add to high word
TFR D,Y ; high 16 bits
LDD PROD+2 , SP ; low 16 bits
*
LEAS 12, SP ; remove M, N, and PROD
JMP 0, X ; return
Figure 7.17.32-Bit by 32-Bit Unsigned Multiply Subroutine
LCSAVE: EQU *
ORG 0
RTRN: DS.W 1
COUNT: DS.B 1
DVS: DS.L 1
REM: DS.L 1
QUOT: DS.L 1

Figure 7.18. 32-Bit by 32-Bit Unsigned Divide Subroutine