bitshift multiplication

; ---------------------------------------------------------------------------
; macro to convert multiplication to bit shift (w)
; in:
; \1 =  input number
; out:
; \2 =  output register
; to-do: esto es mulu, después hacer un muls, divu, divs?
; ---------------------------------------------------------------------------

omulu:      macro
__sp:       = 0
@do:        macro
        n:  = \1
        i:  = 0
        while   n>1
            n:  = n>>1
            i:  = i+1
        endw
        if  i>8*2
            inform  0,"Warning! Overflow will always give zero result"
            moveq   #0,\2
            mexit
        endif
        if  (1*\1)<>(1<<i)
            __sp:   = __sp+1
            t:  = ((\1)-1<<i)

            pushp   '\#n'
            pushp   '\#i'
            move.w  \2,-(__sp*2+2)(sp)      ; -> Very slow #1
            @do t,\2
            move.w  \2,-(sp)
            move.w  -(4-2)(sp),\2           ; -> Very slow #2
            popp    bi
            popp    bn
            n:  = \bn
            i:  = \bi
        endif
        while   i>=8
            ;lsl.w  #8,\2
                clr.w   -(sp)
                move.b  \2,(sp)
                move.w  (sp)+,\2
            i:  = i-8
        endw
        if  i<=2
            rept    i
            add.w   \2,\2
            endr
        else
            lsl.w   #i,\2
        endif
        endm
        @do \1, \2
        rept    __sp
        add.w   (sp)+,\2
        endr
        endm