about nasm

["Tristan Li" <linuxren@xxxxxxxxx>]

Hi nerds:

I've been reading an article on the booting process. The part about detecting the memory amount really confused me.

wrnum:

	push si
	push dx

	push cx
	push ax
		mov si,num_buf


; extended precision division from section 9.3.5
; of Randall Hyde's "Art of Assembly"

; start: DX=dividend MSW, AX=dividend LSW, BX=divisor
wrnum1:

		push ax
			mov ax,dx

			xor dx,dx

; before div: DX=0, AX=dividend MSW, BX=divisor

; after div:  AX=quotient MSW, DX=intermediate remainder
			div bx

			mov cx,ax
		pop ax

; before div: DX=intermediate remainder, AX=dividend LSW, BX=divisor

; after div:  AX=quotient LSW, DX=remainder
		div bx


; end: DX=quotient MSW, AX=quotient LSW, CX=remainder
		xchg dx,cx

		add cl,'0'
		cmp cl,'9'

		jbe wrnum2
		add cl,('A'-('9'+1))
wrnum2:

		dec si
		mov [si],cl


		mov cx,ax
		or cx,dx
		jne wrnum1

		call cputs
	pop ax
	pop cx

	pop dx
	pop si

	ret

I'm just wondering what's the code above doing? I really can not understand it.
Can anyone help me? 
Many thx!
The original code can be found at 
http://my.execpc.com/~geezer/osd/boot/size.asm
Sorry for my english :-(

-- 
My blog: http://lijie.org