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range: Replace internal representation of Range

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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>
This commit is contained in:
Markus Armbruster 2016-07-01 13:47:48 +02:00 • committed by Michael S. Tsirkin
parent a0efbf1660
commit 6dd726a2bf
2 changed files with 34 additions and 38 deletions
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16
util/range.c
View file

@ -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;