range: Replace internal representation of Range
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.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
diff --git a/util/range.c b/util/range.c
index e5f2e71..416df7c 100644
--- a/util/range.c
+++ b/util/range.c
@@ -22,20 +22,18 @@
#include "qemu/range.h"
/*
- * Operations on 64 bit address ranges.
- * Notes:
- * - ranges must not wrap around 0, but can include the last byte ~0x0LL.
- * - this can not represent a full 0 to ~0x0LL range.
+ * Return -1 if @a < @b, 1 @a > @b, and 0 if they touch or overlap.
+ * Both @a and @b must not be empty.
*/
-
-/* Return -1 if @a < @b, 1 if greater, and 0 if they touch or overlap. */
static inline int range_compare(Range *a, Range *b)
{
- /* Zero a->end is 2**64, and therefore not less than any b->begin */
- if (a->end && a->end < b->begin) {
+ assert(!range_is_empty(a) && !range_is_empty(b));
+
+ /* Careful, avoid wraparound */
+ if (b->lob && b->lob - 1 > a->upb) {
return -1;
}
- if (b->end && a->begin > b->end) {
+ if (a->lob && a->lob - 1 > b->upb) {
return 1;
}
return 0;
