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;* MulLong - Multiplies two unsigned double-word (long) integers. The
;* procedure allows for a product of twice the length of the multipliers,
;* thus preventing overflows. The result is copied into a 4-word data area
;* and a pointer to the data area is returned.
;*
;* Shows:   Instruction - mul
;*          Predefined equate - @data
;*
;* Params:  Long1 - First integer (multiplicand)
;*          Long2 - Second integer (multiplier)
;*
;* Return:  Pointer to quadword result
 
        .DATA
        PUBLIC result
result  QWORD   WORD PTR ?              ; Result from MulLong
 
        .CODE
MulLong PROC,
        Long1:DWORD, Long2:DWORD
 
        mov     ax, WORD PTR Long2[2]   ; Multiply long2 high word
        mul     WORD PTR Long1[2]       ;   by long1 high word
        mov     WORD PTR result[4], ax
        mov     WORD PTR result[6], dx
 
        mov     ax, WORD PTR Long2[2]   ; Multiply long2 high word
        mul     WORD PTR Long1[0]       ;   by long1 low word
        mov     WORD PTR result[2], ax
        add     WORD PTR result[4], dx
        adc     WORD PTR result[6], 0   ; Add any remnant carry
 
        mov     ax, WORD PTR Long2[0]   ; Multiply long2 low word
        mul     WORD PTR Long1[2]       ;   by long1 high word
        add     WORD PTR result[2], ax
        adc     WORD PTR result[4], dx
        adc     WORD PTR result[6], 0   ; Add any remnant carry
 
        mov     ax, WORD PTR Long2[0]   ; Multiply long2 low word
        mul     WORD PTR Long1[0]       ;   by long1 low word
        mov     WORD PTR result[0], ax
        add     WORD PTR result[2], dx
        adc     WORD PTR result[4], 0   ; Add any remnant carry
 
        mov     ax, OFFSET result       ; Return pointer
        mov     dx, @data               ;   to result
        ret
 
MulLong ENDP
                                    -♦-