global Mul
global Div

; input: [esp+4] m
;        [esp+8] n
; return: eax low word of product
;         edx high word of product
Mul:
    push esi
    push edi

    ; ecx n
    mov ecx,[esp+12]
    ; esi,edi m
    mov edi,[esp+16]
    xor esi,esi
    ; edx,eax p
    xor eax,eax
    xor edx,edx

    and ecx,ecx
    jz .done
.loop:
    shr ecx,1
    jnc .zerobit
    add eax,edi
    adc edx,esi
.zerobit:
    shl edi,1
    rcl esi,1
    and ecx,ecx
    jnz .loop

.done:
    pop edi
    pop esi
    ret


; quotient in eax
; remainder in edx

Div:
    push ebx
    push esi

    xor eax,eax      ; q
    mov ebx,[esp+16] ; d
    xor edx,edx      ; r
    mov esi,[esp+12] ; n

    mov ecx,32       ; i
.loop:
    shl eax,1
    shl edx,1
    shl esi,1
    adc edx,0
    cmp edx, ebx
    jl .ge
    sub edx, ebx
    add eax,1
.ge:
    dec ecx
    jnz .loop

.done:
    pop esi
    pop ebx
    ret

; vim:ft=nasm