Shareware Grab Bag/Shareware Grab Bag.iso/007/asm_subr.arc/MBINDIV

Text File | 1985-12-28 | 5.0 KB | 208 lines

;-------------------------mbindiv routine begins--------------------------+
; from BLUEBOOK OF ASSEMBLY ROUTINES FOR IBM PC & XT.
;         page : 122
;
; NAME  MBINDIV
;
; ROUTINE FOR Multidigit Binary DIVISION
;
; FUNCTION: This routine divides two multidigit binary numbers, producing
; both a quotient and remainder.
;
; INPUT: Upon entry DS:SI points to the divisor; DS:BX points to where
; the dividend is upon entry and where the remainder will be upon exit,
; and DS:DI points to the location where the quotient will be upon exit.
; The size of these multidigit numbers is controlled by the constant
; ISIZE.  The divisor and quotient contain 16*ISIZE number of
; bits and the dividend and remainder have double that precision.
; Both the divisor and the quotient are stored in ISIZE number of 16-bit
; words of memory and the dividend and remainder are stored in 2*ISIZE
; number of 16-bit words of memory.
;
; OUTPUT: Upon exit DS:BX points to where the quotient is stored and
; DS:DI points to where the remainder is stored.
;
; REGISTERS USED:  No registers are modified.
;
; SEGMENTS REFERENCED:  Upon entry the data segment must contain
; storage for the multidigit numbers described above.
;
; ROUTINES CALLED:  None
;
; SPECIAL NOTES: None
;
; LOCAL SUBROUTINE TO COMPARE DIVISOR AGAINST DIVIDEND
;
divcmp    proc    near
;
    push    si        ; save registers
    push    di
    push    cx
;
    std            ; backward direction
    add    si,4*isize-2    ; point to end of temp divisor
    add    di,4*isize-2    ; point to end of quotient
    mov    cx,2*isize    ; count for double precision
;
    repz    cmpsw        ; compare 'digit' by 'digit'
;
    pop    cx        ; restore registers
    pop    di
    poop    si
    ret            ; return from divcmp
;
; LOCAL SUBROUTINE FOR ARITHMETIC SHIFT DIVISOR LEFT
;
divsal    proc    near
;
    push    si        ; save registers
    push    cx
;
    mov    cx,2*isize    ; set counter
    clc            ; clear carry in
;
divsal1:
    rcl    word ptr [si],1    ; shift one word by one bit
    inc    si        ; point to next word
    inc    si
    loop    divsal1        ; loop through entire divisor
;
    pop    cx        ; restore registers
    pop    si
    ret            ; return from divsal
;
divsal    endp
;
; LOCAL SUBROUTINE FOR LOGICAL SHIFT DIVISOR RIGHT
;
divslr    proc    near
;
    push    si        ; save registers
    push     cx
;
    add    si,4*isize-2    ; poin to end of temp divisor
    mov    cx,2*isize    ; count for double precision
    clc            ; clear carry in
;
divslr1:
    rcr    word ptr [si],1    ; shift one word by one bit
    inc    si        ; point to next word
    inc    si
    loop    divslr1        ; loop through entire divisor
;
    pop    cx        ; restore registers
    pop    si
    ret            ; return from divslr
;
divslr    endp
;
; LOCAL SUBROUTINE TO SUBTRACT SHIFTED DIVISOR FROM DIVIDEND
;
divsub    proc    near
;
    push    si        ; save registers
    push    di
    push    cx
;
    clc            ; clear carry in
    mov    cx,2*isize    ; set count fop double precision
;
divsub1:
    mov    ax,[si]        ; get word from shifted divisor
    inc    si        ; point to next word
    inc    si
    sbb    [di],ax        ; subtract from word of dividend
    inc    di        ; point to next word
    inc    di
    loop    divsub1        ; loop through all words
;
    pop    cx
    pop    di
    pop    si
;
    ret            ; return from divsub
;
divsub    endp
;
; LOCAL SUBROUTINE TO SHIFT QUOTIENT LEFT
;
quotshl    proc    near
;
    push    bx        ; save registers
    push    cx
;
    mov    cx,isize    ; count for single precision
;
quotshl1:
    rcl    word ptr [bx],1    ; shift word of quotient left once
    inc    bx        ; point to next word
    inc    bx
    loop    quotshl1    ; loop through entire quotient
;
    pop    cx        ; restore registers
    pop    bx
    ret            ; retirn from quotshl
;
quotshl    endp
;
; ROUTINE TO DIVIDE MULTIDIGIT BINARY NUMBERS
;
mbindiv    proc    far
;
    push    si        ; save registers
    push    di
    push    bx
    push    cx
    push    ax
;
; put single precision divisor into double precision location
    push    di        ; save dividend pointer
    lea    di,tempdiv    ; point to temporary divisor
    mov    cx,isize    ; for a count of isize
    cld            ; forward direction
    rep    movsw        ; make the transfer
;
; clear upper part of double precision location
    mov    ax,0        ; zero word
    mov    cx,isize    ; for a count of isize
    rep    stosw        ; clear the rest of the words
;
; restore dividend pointer and point to temp divisor
    pop    di        ; restore dividend pointer
    lea    si,tempdiv    ; point SI to temporary divisor
;
; initialize shift count
    mov    cx,1        ; initial count of one
;
; normalize divisor
mbindiv1:
    test    msbdiv,8000h    ; test msb of divisor
    jnz    mbindiv2    ; exit if normalized
    call    divsal        ; arithmetic shift if not
    inc    cx        ; count the shift
    jmp    mbindiv1    ; keep on looping until normalized
;
; compare, subtract, shift loop
mbindiv2:
    call    divcmp        ; compare divisor against dividend
    ja    mbindiv3    ; skip if too large
    call    divsub        ; subtract if OK
    stc            ; new bit of quotient is 1
    jmp    mbindiv4    ; jump to end of loop
;
mbindiv3:
    clc            ; new bit of quotient is 0
;
mbindiv4:
    call    quotshl        ; shift bit into the quotient
    call    divslr        ; logical shift divisor right once
    loop    mbindiv2    ; loop for next digit
;
    pop    ax        ; restore registers
    pop    cx
    pop    bx
    pop    di
    pop    si
;
mbindiv    endp
;-------------------------mbindiv routine ends---------------------------