Voyager #03 19 октября 1998

Программирование

Laboratory - The algorithm of division and multiplication of large numbers.

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     The second program (or rather two of them) implements
fast algorithms for division and multiplication of large 
numbers. On this basis, it is easy to write the p / n decimal 
numbers in the registers (the conversion line in number).


Designation:


MUL_HLBC_DE: Registers HLBC = HLBC * DE


DIV_HLBC_DE: Registers HLBC = HLBC / DE



     Entry point MUL16 and DIV16, as follows from
names, perform the multiplication and division of 16-bit
numbers. And, if multiplied by 16 bits at 16, then
result is 32 bits.

;====================================
, 16-BIT MULTIPLY
;====================================
MUL16: LD HL, 0
MUL_HLBC_DE:

        LD A, B

        LD B, 11H

        JR L4928
L4921: JR NC, L4924

        ADD HL, DE
L4924: RR H

        RR L
L4928: RRA

        RR C

        DJNZ L4921

        LD B, A

        RET
;====================================
, 16-BIT DIVIDE
;====================================
DIV16: LD HL, 0
DIV_HLBC_DE:

        LD A, B

        LD B, 10H

        RL C

        RLA
L493B: RL L

        RL H

        JR C, L494E

        SBC HL, DE

        JR NC, L4946

        ADD HL, DE
L4946: CCF
L4947: RL C

        RLA

        DJNZ L493B

        LD B, A

        RET
L494E: OR A

        SBC HL, DE

        JR L4947



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     Well, like it is all for today. Yes, a little
do not forget: all these applets written somewhere in the
1983 was none other than Tim Paterson, author of MSX-DOS
and the first version of MS-DOS. Such are the things ...