Re: Integer division in Lua with numbers as longs

[David Jones <drj@...>]

On Apr 18, 2006, at 01:26, Reuben Thomas wrote:

> On Tue, 17 Apr 2006, John D. Ramsdell wrote:
>
> > > A user of the patch has suggested to me that Lua's division and
> > > modulus operator should satisfy the same equation as C's integer
> > > division and remainder operators.
> >
> > I see this topic was recently discussed in another thread I happened
> > not to be following.  I concluded that integer division should work as
> > it does in Python, and changed the patch to define division as
> > follows.
> >
> > #define luai_numdiv(a,b) ((a)<0==(b)<0||(a)%(b)==0?(a)/(b):(a)/(b)-1)
>
> This is not reliable: ANSI/ISO C does not specify how integer division 
> is rounded (to zero or to -infinity).

The 1999 C standard does.  And it specifies round towards zero (which 
in my opinion is completely broken).

Previous versions of the C standard allowed the implementation to 
select either style of rounding.

For personal reasons I'd love to know about any platform where someone 
has observed C's integer division rounding towards -inf.

drj