Re: MATH_MOD: Include in GLib?



On Mon, 2004-07-26 at 06:41, Sven Neumann wrote:
> Hi,
> 
> Jan Kratochvil <lace jankratochvil net> writes:
> 
> > On Mon, 26 Jul 2004 10:43:21 +0200, Sven Neumann wrote:
> > > Daniel Brockman <drlion deepwood net> writes:
> > ...
> > > > #define MOD(x, m) ((x) >= 0 ? (x) % (m) : (m) + (x) % (m))
> > ...
> > > If at all it would have to be G_MOD(x). But I doubt that
> > > the semantics of such a macro are obvious enough and that it would be
> > > of general usefulness.
> > 
> > I consider this macro as a generally used workaround of a bug in C standard.
> > I intuitively expect the result of "x%m" will be 0..(m-1), not the C result
> > of -(m-1)..(m-1).  It has similiar position as G_N_ELEMENTS().
> 
> The result of "x%m" will be 0..(m-1) provided that you respect the
> fact that the modulo operator is undefined on negative operands. The
> behaviour is machine-dependent and you should simply avoid to use
> modulo with signed variables.

Are you sure about this? In my understanding, the C standard defines
division as truncation towards zero. And then defines:

 a % b == a - b * (a / b)

Regards,
						Owen

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