Category : Assembly Language Source Code
Archive   : FP16.ZIP
Filename : MUL.ASM

Page 58, 80
comment |

Date: 10/22/92
Name: Mul.asm
Author: Michael J. Steiner

description: Assembly function to multiply to long's
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.model small
.code

public _Multiply
_Multiply proc

push bp
mov bp,sp
sub sp,0004 ;stack alignment

mov cx,[ bp + 06h ] ;lsb of number0
mov bx,[ bp + 04h ] ;msb of number0
mov dx,[ bp + 0Ah ] ;lsb of number1
mov ax,[ bp + 08h ] ;msb of number1

push si ;save contents of si

xchg si,ax ;save ax in si
xchg dx,ax ;xchange ax and dx for test
test ax,ax ;check exist lsb number1
jz Skip1 ;no bits set move on
mul bx ;yes lsb num1 * msb num0
Skip1:
jcxz Skip2 ;jump if lsb num0 is zero
xchg cx,ax ;no xchange ax and cx
mul si ;msb num1 * lsb num0
add ax,cx ;add first result to second
Skip2:
xchg si,ax ;msb num1 back to ax,si result
mul bx ;msb num0 * msb num1
add dx,si ;add msb resutant to msb
;return
pop si ;restore old si
mov sp,bp ;realign stack
pop bp ;restore old bp

ret ;dx:ax holds return value
_Multiply endp
end