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CICA 1993 April
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CICA MS Windows - April 1993.iso
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ptv2n5
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l2.asm
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Assembly Source File
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1991-09-07
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2KB
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68 lines
; Divides an arbitrarily long unsigned dividend by a 16-bit unsigned
; divisor. C near-callable as:
; unsigned int Div(unsigned int * Dividend,
; int DividendLength, unsigned int Divisor,
; unsigned int * Quotient);
;
; Returns the remainder of the division.
;
; Tested with TASM 2.
parms struc
dw 2 dup (?) ;pushed BP & return address
Dividend dw ? ;pointer to value to divide, stored in Intel
; order, with lsb at lowest address, msb at
; highest. Must be composed of an integral
; number of words
DividendLength dw ? ;# of bytes in Dividend. Must be a multiple
; of 2
Divisor dw ? ;value by which to divide. Must not be zero,
; or a Divide By Zero interrupt will occur
Quotient dw ? ;pointer to buffer in which to store the
; result of the division, in Intel order.
; The quotient returned is of the same
; length as the dividend
parms ends
.model small
.code
public _Div
_Div proc near
push bp ;preserve caller's stack frame
mov bp,sp ;point to our stack frame
push si ;preserve caller's register variables
push di
std ;we're working from msb to lsb
mov ax,ds
mov es,ax ;for STOS
mov cx,[bp+DividendLength]
sub cx,2
mov si,[bp+Dividend]
add si,cx ;point to the last word of the dividend
; (the most significant word)
mov di,[bp+Quotient]
add di,cx ;point to the last word of the quotient
; buffer (the most significant word)
mov bx,[bp+Divisor]
shr cx,1
inc cx ;# of words to process
sub dx,dx ;convert initial divisor word to a 32-bit
; value for DIV
DivLoop:
lodsw ;get next most significant word of divisor
div bx
stosw ;save this word of the quotient
;DX contains the remainder at this point,
; ready to prepend to the next divisor word
loop DivLoop
mov ax,dx ;return the remainder
cld ;restore default Direction flag setting
pop di ;restore caller's register variables
pop si
pop bp ;restore caller's stack frame
ret
_Div endp
end