qemu/util/range.c
Markus Armbruster 6dd726a2bf 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>
2016-07-04 16:49:33 +03:00

74 lines
2.1 KiB
C

/*
* QEMU 64-bit address ranges
*
* Copyright (c) 2015-2016 Red Hat, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU General Public
* License along with this library; if not, see <http://www.gnu.org/licenses/>.
*
*/
#include "qemu/osdep.h"
#include "qemu/range.h"
/*
* Return -1 if @a < @b, 1 @a > @b, and 0 if they touch or overlap.
* Both @a and @b must not be empty.
*/
static inline int range_compare(Range *a, Range *b)
{
assert(!range_is_empty(a) && !range_is_empty(b));
/* Careful, avoid wraparound */
if (b->lob && b->lob - 1 > a->upb) {
return -1;
}
if (a->lob && a->lob - 1 > b->upb) {
return 1;
}
return 0;
}
/* Insert @data into @list of ranges; caller no longer owns @data */
GList *range_list_insert(GList *list, Range *data)
{
GList *l;
assert(!range_is_empty(data));
/* Skip all list elements strictly less than data */
for (l = list; l && range_compare(l->data, data) < 0; l = l->next) {
}
if (!l || range_compare(l->data, data) > 0) {
/* Rest of the list (if any) is strictly greater than @data */
return g_list_insert_before(list, l, data);
}
/* Current list element overlaps @data, merge the two */
range_extend(l->data, data);
g_free(data);
/* Merge any subsequent list elements that now also overlap */
while (l->next && range_compare(l->data, l->next->data) == 0) {
GList *new_l;
range_extend(l->data, l->next->data);
g_free(l->next->data);
new_l = g_list_delete_link(list, l->next);
assert(new_l == list);
}
return list;
}