Junio C Hamano <gitster@xxxxxxxxx> writes:
> Would it make sense to go one step further to introduce two macros
> to make this kind of screw-up less likely?
> ...
> After letting my eyes coast over hits from "git grep memmove", there
> do seem to be some places that these would help readability, but not
> very many.
I see quite a many hits that follow this pattern
memmove(array + pos, array + pos + 1, sizeof(*array) * (nr - pos))
to make a single slot in a middle of array available, which would be
good candidates to use MOVE_DOWN(). Just to show a few:
builtin/mv.c:226: memmove(source + i, source + i + 1,
builtin/mv.c-227- (argc - i) * sizeof(char *));
builtin/mv.c:228: memmove(destination + i,
builtin/mv.c-229- destination + i + 1,
builtin/mv.c-230- (argc - i) * sizeof(char *));
cache-tree.c:92: memmove(it->down + pos + 1,
cache-tree.c-93- it->down + pos,
cache-tree.c-94- sizeof(down) * (it->subtree_nr - pos - 1));
Perhaps something like this patch to start off; I am not sure
MOVE_DOWN_BOUNDED is needed, though.
cache.h | 33 +++++++++++++++++++++++++++++++++
1 file changed, 33 insertions(+)
diff --git a/cache.h b/cache.h
index b66cb49..b2615ab 100644
--- a/cache.h
+++ b/cache.h
@@ -455,6 +455,39 @@ extern int daemonize(void);
} \
} while (0)
+/*
+ * With an array "array" that currently holds "nr" elements, move
+ * elements at "at" and later down by "count" elements to make room to
+ * add in new elements. The caller is responsible for making sure
+ * that the array has enough room to hold "nr" + "count" slots.
+ */
+#define MOVE_DOWN(array, nr, at, count) \
+ memmove((array) + (at) + (count), \
+ (array) + (at), \
+ sizeof((array)[0]) * ((nr) - (at)))
+
+/*
+ * With an array "array" that has enough memory to hold "alloc"
+ * elements allocated and currently holds "nr" elements, move elements
+ * at "at" and later down by "count" elements to make room to add in
+ * new elements.
+ */
+#define MOVE_DOWN_BOUNDED(array, nr, at, count, alloc) \
+ do { \
+ if ((alloc) <= (nr) + (count)) \
+ BUG("MOVE_DOWN beyond the end of an array"); \
+ MOVE_DOWN((array), (nr), (at), (count)); \
+ } while (0)
+
+/*
+ * With an array "array" that curently holds "nr" elements, move elements
+ * at "at" + "count" and later down by "count" elements, removing the
+ * elements between "at" and "at" + "count".
+ */
+#define MOVE_UP(array, nr, at, count) \
+ memmove((array) + (at), (array) + (at) + (count), \
+ sizeof((array)[0]) * ((nr) - ((at) + (count))))
+
/* Initialize and use the cache information */
extern int read_index(struct index_state *);
extern int read_index_preload(struct index_state *, const struct pathspec *pathspec);
--
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