On 06/15/2016 02:41 PM, Markus Armbruster wrote: > Range represents a range as follows. Member @start is the inclusive > lower bound, member @end is the exclusive upper bound. Zero @end is > special: if @start is also zero, the range is empty, else @end is to > be interpreted as 2^64. No other empty ranges may occur. > > The range [0,2^64-1] cannot be represented. If you try to create it > with range_set_bounds1(), you get the empty range instead. If you try > to create it with range_set_bounds() or range_extend(), assertions > fail. Before range_set_bounds() existed, the open-coded creation > usually got you the empty range instead. Open deathtrap. > > Moreover, the code dealing with the janus-faced @end is too clever by > half. > > Dumb this down to a more pedestrian representation: members @lob and > @upb are inclusive lower and upper bounds. The empty range is encoded > as @lob = 1, @upb = 0.
And since all users now go through accessors, we've freed ourselves to
change the underlying representation.
>
> Signed-off-by: Markus Armbruster <arm...@redhat.com>
> ---
> include/qemu/range.h | 55
> +++++++++++++++++++++++++---------------------------
> util/range.c | 13 +++----------
> 2 files changed, 29 insertions(+), 39 deletions(-)
Not only does it have more power, it takes fewer lines of code!
>
> /* Compound literal encoding the empty range */
> -#define range_empty ((Range){ .begin = 0, .end = 0 })
> +#define range_empty ((Range){ .lob = 1, .upb = 0 })
well, one particular representation of the empty range, but the comment
is fine as-is.
Reviewed-by: Eric Blake <ebl...@redhat.com>
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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