qsort compare functions

[Matthias Andree]

David Relson <relson at osagesoftware.com> writes:

> Qsort simply wants to know how to order two items.  Bogofilter wants
> them in probability order (primarily) and  alphabetic order
> (secondarily).  Given this info, I assert that the proper code is:
>
>      const discrim_t *d1 = id1;
>      const discrim_t *d2 = id2;
>
>      if (d1->prob > d2->prob) return 1;
>      if (d1->prob < d2->prob) return -1;
>      return strcmp(d1->key, d2->key);
>
> If there are no objections, I shall make this correction.

Object. This assumes we have a clear == semantic for double, which we
don't really have. The EPS stuff is there to kill rounding errors.

My code checks if d1->prob and d2->prob are close enough to each other
to consider them equal.

Remember: (1.0/3)*3 == 1.0 does not hold, and therefore < or > may match
even though the values are "equal" in the rounding error constraints
(EPS even).

-- 
Matthias Andree