Re: MATH_MOD: Include in GLib?

[Jan Kratochvil <rcpt-gtk-devel-list AT gnome org jankratochvil net>]

Hi Owen,

On Mon, 26 Jul 2004 14:23:42 +0200, Owen Taylor wrote:
...
> You also usually want the equivalent division at the same time:

/* Provide C modulo (x % m) with defined result for m<0
 * always in the range of 0..(m-1).
 * `x' and `m' must be integers. `m' must != 0.
 */
#define G_MOD(x, m) ((x) >= 0 ? (x) % (m) : (m) - 1 - ((-(x) - 1) % (m)))

/* Provide C division (x / m) compatible with G_MOD() even for m<0:
 * x == G_DIV(x, m) * m + G_MOD(x, m)
 * `x' and `m' must be integers. `m' must != 0.
 */
#define G_DIV(x, m) ((x) / (m) - ((x) >= 0 || 0 == (-(x)) % (m) ? 0 : 1))


> It's worth noting that powers of two can be optimized for this:
> 
>  MOD(x, 1024) = x >> 10
>  DIV(x, 1024) = x & 1023
                  x & ((1<<10)-1) would be IMO more clear


Regards,
Lace

-- 
Jan Kratochvil; Captive: free r/w NTFS Filesystem; http://www.jankratochvil.net/