Category : Assembly Language Source Code
Archive   : ASM-SUBR.ZIP
Filename : MBINMUL

;-------------------------mbinmul routine begins--------------------------+
; from BLUEBOOK OF ASSEMBLY ROUTINES FOR IBM PC & XT.
; page : 120
;
; NAME MBINMUL
;
; ROUTINE FOR Multidigit Binary Multiplication
;
; FUNCTION: This routine multiplies two multidigit binary numbers.
;
; INPUT: Upon entry DS:SI points to the first number; DS:DI points to
; the second number, and DS:BX points to the location where the result
; will be stored. The size of these multidigit numbers is controlled
; by the constant ISIZE. The input numbers contain 16*ISIZE number of
; bits and the output number has double that precision. Both inputs are
; stored in ISIZE number of 16-bit words of memory and the output is
; stored in 2*ISIZE number of 16-bit words of memory.
;
; OUTPUT: Upon exit DS:BX points to where the result is stored.
;
; REGISTERS USED: No registers are modified.
;
; SEGMENTS REFERENCED: Upon entry the data segment must contain
; storage for three multidigit numbers; two for input and one for output.
;
; ROUTINES CALLED: None
;
; SPECIAL NOTES: None
;
; ROUTINE TO MULTIPLY MULTIDIGIT BINARY NUMBERS
;
mbinmul proc far
;
push si ; save registers
push di
push bx
push cx
push ax
;
; clear result buffer
push bx ; save result pointer BX
mov ax,0 ; get a zero
mov cx,2*isize ; double precision for this number
cld ; forward direction
;
mbinmul1:
mov [bx],ax ; clear the 'digit'
inc bx ; point to next 'digit'
inc bx
loop mbinmul1 ; loop through all 'digitts'
pop bx ; store result pointer BX
;
mov cx,isize ; get the number of 16-bit 'digits'
;
mbnimul2:
push cx ; save counter from outter loop
mov dx,[si] ; get 'digit'' from 1st number
inc si ; point to next number
inc si
;
push bx ; save register during inner loop
push di
;
mov cx,isize ; get the number of 16-bit 'digits'
;
mbinmul3:
push cx ; save counter for inner loop
push dx ; save multiplier digit
mov ax,[di] ; get 'digit' from 2nd number
inc di ; point to next 'digit'
inc di
mul dx ; multiply
add [bx],ax ; add lower 'digit' to result
inc bx ; point to next 'digit'
inc bx
adc [bx],dx ; add upper part to result
pop dx ; restore multiplier
pop cx ; restore counter for inner loop
loop mbinmul3 ; loop through all 'digits' of second
;
pop di ; restore registers
pop bx
;
inc bx ; shift by on 'digit'
inc bx
pop cx ; restore counter for outer loop
loop mbinmul2 ; loop through all 'digits' of first
;
pop ax ; restore registers
pop cx
pop bx
pop di
pop si
ret
;
ret ; return
;
mbinmul endp
;-------------------------mbinmul routine ends---------------------------