I was under the impression that, unlike multiplication, it's not easy to
break (for example) a 32 bit divide operation into multiple 16 bit ones.

To do this with multiplication is relatively easy:
C =3D A * B
C =3D AL * BL + AL * BH + AH * BL + AH * BH

David.

On Wed, Oct 17, 2012 at 7:56 PM, Joe Mickley <joemickley@comcast.net> wrote=
:

> I am using a dsPIC30F3012 (writing in ASM, not C) on a project with very
> fast loop execution (<20 uSec in some cases)
> and need an effecient 32 bit by 32 bit unsigned divide algorithm.  The
> dsPIC30F family has organic 16 by 16 divide
> instruction (DIV.U and DIV.UD) and I would like to create a 32 by 32 usin=
g
> that instruction set.
>
> The traditional 32 by 32 divide using a shift/subtract (restoring)
> algorithms is slow (about 400 instruction cycles nominal). It
> should be possible to break the 32 by 32 into a set of 16 by 16 operation=
s,
> then combine the partials back into a 32 by 32
> result, but I lack the knowledge of how to do or drive this.  The dsPIC30=
F
> divide routine is fast (18 cycles, so
> any use of itshould have a marked improvement)
>
> I need an unsigned divide, but could live with a signed divide as the
> magnitude of numbers I am working with are less than
> 2^30.  Remainder or lack of is not critical.  If I need it I could derive=
 a
> remainder externally to the routine.
>
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