Re: implementing software unsigned divide

[Tucker Taft <stt@averstar.com>]

Stephen Leake wrote:
> 
> I'm porting GNAT to a 16 bit microprocessor that does not provide a
> hardware instruction for unsigned divide (it has multiply and signed
> divide, both 16 and 32 bit). Can anyone provide a reference to a book
> that discusses how to do this, and/or an algorithm that does it? I've
> looked in Knuth, and did an initial web search, and haven't found
> anything.

This is generally pretty straightforward using the
signed hardware instructions, and some appropriate
amount of fixups before and/or after the actual divide.
I suggest you try some specific examples by hand where one or
both of the values have the high bit on.  It is pretty
easy to figure out what sort of fixup, if any, is
necessary.

I have done this myself in the past, but unfortunately I didn't
write down the algorithms in a place that I can locate
at the moment.

> 
> --
> -- Stephe

-- 
-Tucker Taft   stt@avercom.net   http://www.averstar.com/~stt/
Chief Technology Officer, AverCom Corporation (A Titan Company) 
Burlington, MA  USA (AverCom was formerly the Commercial Division of AverStar:
http://www.averstar.com/services/ebusiness_applications.html)