Difference between revisions of "Programming:Integer Division"

Revision as of 11:23, 14 November 2015

8bit division

Input: HL=Value1, C=Value2

Output: L=Value1/Value2, H=Value1 MOD Value2

Destroyed: AF,BC

        LD B,8
Div_Next:
        ADD     HL,HL
        LD      A,H
        SUB     C
        JR      C,Div_NXTB
        LD      H,A
        INC     L
Div_NXTB:
        DJNZ    Div_Next
        RET

16bit division

Input: BC=Value1, DE=Value2

Output: HL=Value1/Value2, DE=Value1 MOD Value2

Destroyed: AF,BC

clcd16  ld a,e
        or d
        ld hl,0
        ret z
        ld a,b
        ld b,16
clcd161 rl c
        rla
        adc hl,hl
        sbc hl,de
        jr nc,clcd162
        add hl,de
clcd162 ccf
        djnz clcd161
        ex de,hl
        rl c
        rla
        ld h,a
        ld l,c
        ret

24bit division

Input: A,BC=Value1, DE=Value2

Output: HL=Value1/Value2, DE=Value1 MOD Value2

Destroyed: AF,BC,IX,IYL

clcdiv  db #dd:ld l,e
        db #dd:ld h,d   ;IX=Value2
        ld e,a          ;E,BC=Value1(Counter)
        ld hl,0
        db #dd:ld a,l
        db #dd:or h
        ret z
        ld d,l          ;D,HL=CalcVar
        db #fd:ld l,24  ;IYL=Counter
clcdiv1 rl c
        rl b
        rl e
        rl l
        rl h
        rl d
        ld a,l
        db #dd:sub l
        ld l,a
        ld a,h
        db #dd:sbc h
        ld h,a
        ld a,d
        sbc 0
        ld d,a          ;D,HL=D,HL-IX
        jr nc,clcdiv2
        ld a,l
        db #dd:add l
        ld l,a
        ld a,h
        db #dd:adc h
        ld h,a
        ld a,d
        adc 0
        ld d,a
        scf
clcdiv2 ccf
        db #fd:dec l
        jr nz,clcdiv1
        ex de,hl        ;DE=Value1 MOD Value2
        rl c
        rl b
        ld l,c
        ld h,b          ;HL=Value1 DIV Value2
        ret

32bit division

Input: IY,BC=Value1, IX=Value2

Output: IY,BC=Value1/Value2, HL=Value1 MOD Value2

Destroyed: AF,DE,IY

clcd32c db 0
clcd32  ld hl,0
        db #dd:ld a,l
        db #dd:or h
        ret z           ;IY,BC=Value1(Counter)
        ld de,0         ;DE,HL=CalcVar
        ld a,32         ;Set Counter to 32
clcd321 ld (clcd32c),a
        rl c
        rl b
        db #fd:ld a,l:rla:db #fd:ld l,a
        db #fd:ld a,h:rla:db #fd:ld h,a
        rl l
        rl h
        rl e
        rl d
        ld a,l
        db #dd:sub l
        ld l,a
        ld a,h
        db #dd:sbc h
        ld h,a
        ld a,e
        sbc 0
        ld e,a
        ld a,d
        sbc 0
        ld d,a
        jr nc,clcd322
        ld a,l
        db #dd:add l
        ld l,a
        ld a,h
        db #dd:adc h
        ld h,a
        ld a,e
        adc 0
        ld e,a
        ld a,d
        adc 0
        ld d,a
        scf
clcd322 ccf
        ld a,(clcd32c)
        dec a
        jr nz,clcd321   ;HL=Value1 MOD Value2
        rl c
        rl b
        db #fd:ld a,l:rla:db #fd:ld l,a
        db #fd:ld a,h:rla:db #fd:ld h,a
        ret             ;IY,BC=Value1 DIV Value2

Fast 32bit division

Input: HL,DE=Value1, BC=Value2

Output: BCDE=Value1/Value2, HL=Value1 MOD Value2

Destroyed: AF

Not used: IX, IY

 div macro
     local t1,t2
     ADD   HL, HL
     EX    DE, HL
     ADD   HL, HL
     EX    DE, HL
     JP    NC, t1

     INC   HL
 t1
     LD    A, L
     ADD   A, C
     LD    A, H
     ADC   A, B
     JP    NC, t2

     ADD   HL, BC
     INC   DE
 t2
     endm

 div32x16 proc  ; BCDE = HLDE/BC, HL = HLDE%BC
     local t1, DIV32_, DIV320
     DEC   BC
     LD    A, B
     CPL 
     LD    B, A
     LD    A, C
     CPL 
     LD    C, A
     ADD   A, L
     LD    A, B
     ADC   A, H
     JP    NC, DIV32_

     PUSH  DE
     EX    DE, HL
     LD    HL, 0000
     CALL  DIV320
     EX    DE, HL
     EX    (SP), HL
     EX    DE, HL
     CALL  DIV320
     POP   BC
     RET
 DIV32_
     CALL  DIV320
     LD    BC, 0000
     RET
 DIV320   ; DE = HLDE/(-BC), HL = HLDE%(-BC)
     CALL  t1
 t1
     rept 8
     div
     endm
     RET
     endp 

Web links

• Division implementation for the Sega Master System
• Multiplications and divisions on the MSX Assembly Page