[M3devel] how division and modulo work in hand.c?

[Jay K]

I *speculate*:

   If the inputs to div or mod are known to have the same sign: don't bother calling the functions.

      Certainly that is clear for two positive inputs in the old functions.

   If either input to div is known to be zero, ditto. Presumably not a common case.

      And *maybe* we want to alter how divide by zero works to reliably trap or not trap.

 

  For example, CARDINAL and LONGCARD DIV and MOD need not call the functions ever.

    (again, caveat, maybe for zero, maybe, not currently, but if we make trapping divide by zero controllable)

 

 

 - Jay


 
> From: hosking at cs.purdue.edu
> To: hendrik at topoi.pooq.com
> Date: Sun, 17 Jan 2010 15:19:21 -0600
> CC: m3devel at elegosoft.com
> Subject: Re: [M3devel] how division and modulo work in hand.c?
> 
> It calls the C routines in hand.c.
> 
> Sent from my iPhone
> 
> On Jan 17, 2010, at 2:48 PM, hendrik at topoi.pooq.com wrote:
> 
> > On Sun, Jan 17, 2010 at 11:39:03AM -0500, Tony Hosking wrote:
> >>
> >> This is a quote from the gcc internals manual. I've always wondered
> >> why cm3cg uses the built-in FLOOR_DIV_EXPR/FLOOR_MOD_EXPR only for
> >> known positive operands. What would be wrong about using them also
> >> for negative operands?
> >
> > What does cm3cg use for operands that are not known to be positive?
> >
> > -- hendrik
 		 	   		  
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