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.
Backports commit 6dd726a2bf1b800289d90a84d5fcb5ce7b78a8e1 from qemu
Users of struct Range mess liberally with its members, which makes
refactoring hard. Create a set of methods, and convert all users to
call them instead of accessing members. The methods have carefully
worded contracts, and use assertions to check them.
Backports commit a0efbf16604770b9d805bcf210ec29942321134f from qemu
Commit 7f8f9ef1 introduced the ability to store a list of
integers as a sorted list of ranges, but when merging ranges,
it leaks one or more ranges. It was also using range_get_last()
incorrectly within range_compare() (a range is a start/end pair,
but range_get_last() is for start/len pairs), and will also
mishandle a range ending in UINT64_MAX (remember, we document
that no range covers 2**64 bytes, but that ranges that end on
UINT64_MAX have end < begin).
The whole merge algorithm was rather complex, and included
unnecessary passes over data within glib functions, and enough
indirection to make it hard to easily plug the data leaks.
Since we are already hard-coding things to a list of ranges,
just rewrite the thing to open-code the traversal and
comparisons, by making the range_compare() helper function give
us an answer that is easier to use, at which point we avoid the
need to pass any callbacks to g_list_*(). Then by reusing
range_extend() instead of duplicating effort with range_merge(),
we cover the corner cases correctly.
Drop the now-unused range_merge() and ranges_can_merge().
Doing this lets test-string-{input,output}-visitor pass under
valgrind without leaks.
Backports commit db486cc334aafd3dbdaf107388e37fc3d6d3e171 from qemu
Calling our function g_list_insert_sorted_merged is a misnomer,
since we are NOT writing a glib function. Furthermore, we are
making every caller pass the same comparator function of
range_merge(): any caller that would try otherwise would break
in weird ways since our internal call to ranges_can_merge() is
hard-coded to operate only on ranges, rather than paying
attention to the caller's comparator.
Better is to fix things so that callers don't have to care about
our internal comparator, by picking a function name and updating
the parameter type away from a gratuitous use of void*, to make
it obvious that we are operating specifically on a list of ranges
and not a generic list. Plus, refactoring the code here will
make it easier to plug a memory leak in the next patch.
range_compare() is now internal only, and moves to the .c file.
Backports commit 7c47959d0cb05db43014141a156ada0b6d53a750 from qemu
g_list_insert_sorted_merged() is rather large to be an inline
function; move it to its own file. range_merge() and
ranges_can_merge() can likewise move, as they are only used
internally. Also, it becomes obvious that the condition within
range_merge() is already satisfied by its caller, and that the
return value is not used.
The diffstat is misleading, because of the copyright boilerplate.
Backports commit fec0fc0a13ac7f1a1130433a6740cd850c3db34a from qemu
