| Message ID | 20241220084949.GA132704@coredump.intra.peff.net (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | prio-queue: use size_t rather than int for size | expand |
On Fri, Dec 20, 2024 at 03:49:49AM -0500, Jeff King wrote: > -static inline int compare(struct prio_queue *queue, int i, int j) > +static inline int compare(struct prio_queue *queue, size_t i, size_t j) > { > int cmp = queue->compare(queue->array[i].data, queue->array[j].data, > queue->cb_data); > if (!cmp) > - cmp = queue->array[i].ctr - queue->array[j].ctr; > + cmp = (queue->array[i].ctr > queue->array[j].ctr) - > + (queue->array[i].ctr < queue->array[j].ctr); > return cmp; > } Sorry, just realized that "diff --check" (and apply) complains about the indentation here. It's a TAB followed by 14 spaces, instead of two TABs followed by 6 spaces. I guess caused by me lining things up manually. -Peff
Jeff King <peff@peff.net> writes: > On Fri, Dec 20, 2024 at 03:49:49AM -0500, Jeff King wrote: > >> -static inline int compare(struct prio_queue *queue, int i, int j) >> +static inline int compare(struct prio_queue *queue, size_t i, size_t j) >> { >> int cmp = queue->compare(queue->array[i].data, queue->array[j].data, >> queue->cb_data); >> if (!cmp) >> - cmp = queue->array[i].ctr - queue->array[j].ctr; >> + cmp = (queue->array[i].ctr > queue->array[j].ctr) - >> + (queue->array[i].ctr < queue->array[j].ctr); >> return cmp; >> } > > Sorry, just realized that "diff --check" (and apply) complains about the > indentation here. It's a TAB followed by 14 spaces, instead of two TABs > followed by 6 spaces. I guess caused by me lining things up manually. "git am --whitespace=fix" with or without "-3" corrects such glitches just fine, and "git am --whitespace=error" correctly stops me from applying such a patch. What is worrysome is "git am -3 --whitespace=warn" does not seem to catch it (without "-3" it works just fine). I do not know offhand if this is a recent regression or not.
On Fri, Dec 20, 2024 at 07:27:18AM -0800, Junio C Hamano wrote: > > Sorry, just realized that "diff --check" (and apply) complains about the > > indentation here. It's a TAB followed by 14 spaces, instead of two TABs > > followed by 6 spaces. I guess caused by me lining things up manually. > > "git am --whitespace=fix" with or without "-3" corrects such > glitches just fine, and "git am --whitespace=error" correctly stops > me from applying such a patch. > > What is worrysome is "git am -3 --whitespace=warn" does not seem to > catch it (without "-3" it works just fine). I do not know offhand > if this is a recent regression or not. Interesting. I noticed with stock "git am" (I sometimes "reset --hard" and reapply my own patches because I made tweaks to the commit message while sending). Looks like it does not warn even going back to v2.0.5 (my stock "this was a long time ago" version). Curiously if you accidentally try to apply the patch a second time, it does notice the problem. So I agree it's a bug, but I think it has been around for a while. -Peff
diff --git a/negotiator/skipping.c b/negotiator/skipping.c index abedb70a48..616df6bf3a 100644 --- a/negotiator/skipping.c +++ b/negotiator/skipping.c @@ -134,7 +134,6 @@ static int push_parent(struct data *data, struct entry *entry, struct entry *parent_entry; if (to_push->object.flags & SEEN) { - int i; if (to_push->object.flags & POPPED) /* * The entry for this commit has already been popped, @@ -145,7 +144,7 @@ static int push_parent(struct data *data, struct entry *entry, /* * Find the existing entry and use it. */ - for (i = 0; i < data->rev_list.nr; i++) { + for (size_t i = 0; i < data->rev_list.nr; i++) { parent_entry = data->rev_list.array[i].data; if (parent_entry->commit == to_push) goto parent_found; @@ -248,7 +247,7 @@ static int ack(struct fetch_negotiator *n, struct commit *c) static void release(struct fetch_negotiator *n) { struct data *data = n->data; - for (int i = 0; i < data->rev_list.nr; i++) + for (size_t i = 0; i < data->rev_list.nr; i++) free(data->rev_list.array[i].data); clear_prio_queue(&data->rev_list); FREE_AND_NULL(data); diff --git a/prio-queue.c b/prio-queue.c index 450775a374..d0581dcc5c 100644 --- a/prio-queue.c +++ b/prio-queue.c @@ -1,26 +1,29 @@ #include "git-compat-util.h" #include "prio-queue.h" -static inline int compare(struct prio_queue *queue, int i, int j) +static inline int compare(struct prio_queue *queue, size_t i, size_t j) { int cmp = queue->compare(queue->array[i].data, queue->array[j].data, queue->cb_data); if (!cmp) - cmp = queue->array[i].ctr - queue->array[j].ctr; + cmp = (queue->array[i].ctr > queue->array[j].ctr) - + (queue->array[i].ctr < queue->array[j].ctr); return cmp; } -static inline void swap(struct prio_queue *queue, int i, int j) +static inline void swap(struct prio_queue *queue, size_t i, size_t j) { SWAP(queue->array[i], queue->array[j]); } void prio_queue_reverse(struct prio_queue *queue) { - int i, j; + size_t i, j; if (queue->compare) BUG("prio_queue_reverse() on non-LIFO queue"); + if (!queue->nr) + return; for (i = 0; i < (j = (queue->nr - 1) - i); i++) swap(queue, i, j); } @@ -35,7 +38,7 @@ void clear_prio_queue(struct prio_queue *queue) void prio_queue_put(struct prio_queue *queue, void *thing) { - int ix, parent; + size_t ix, parent; /* Append at the end */ ALLOC_GROW(queue->array, queue->nr + 1, queue->alloc); @@ -58,7 +61,7 @@ void prio_queue_put(struct prio_queue *queue, void *thing) void *prio_queue_get(struct prio_queue *queue) { void *result; - int ix, child; + size_t ix, child; if (!queue->nr) return NULL; diff --git a/prio-queue.h b/prio-queue.h index 4f9a37e6be..36f370625f 100644 --- a/prio-queue.h +++ b/prio-queue.h @@ -30,7 +30,7 @@ struct prio_queue { prio_queue_compare_fn compare; unsigned insertion_ctr; void *cb_data; - int alloc, nr; + size_t alloc, nr; struct prio_queue_entry *array; };
The alloc and nr fields of a prio-queue tell us how much memory is allocated and used in the array. So the natural type for them is size_t, which prevents overflow on 64-bit systems where "int" is still 32 bits. This is unlikely to happen in practice, as we typically use it for storing commits, and having 2^31 of those is rather a lot. But it's good to keep our generic data structures as flexible as possible. And as we start to enforce -Wsign-compare, it means that callers need to use "int", too, and the problem proliferates. Let's fix it at the source. The changes here can be put into a few groups: 1. Changing the alloc/nr fields in the struct to size_t. This requires swapping out int for size_t in negotiator/skipping.c, as well as in prio_queue_get(), because those all iterate over the array. Building with -Wsign-compare complains about these. 2. Other code that assigns or passes around indexes into the array (e.g., the swap() and compare() functions) won't trigger -Wsign-compare because we are simply truncating the values. These are caught by -Wconversion, but I've adjusted them here to future-proof us. 3. In prio_queue_reverse() we compute "queue->nr - 1" without checking if anything is in the queue, which underflows now that nr is unsigned. We can fix that by returning early when the queue is empty (there is nothing to reverse). 4. The insertion_ctr variable is currently unsigned, but can likewise grow (it is actually worse, because adding and removing an element many times will keep increasing the counter, even though "nr" does not). I've bumped that to size_t here, as well. But -Wconversion notes that computing the "cmp" result by subtracting the counters and assigning to "int" is a potential problem. And that's true even before this patch, since we use an unsigned counter (imagine comparing "2^32-1" and "0", which should be a high positive value, but instead is "-1" as a signed int). Since we only care about the sign (and not the magnitude) of the result, we could fix this by swapping out the subtraction for a ternary comparison. Probably the performance impact would be negligible, since we just called into a custom compare function and branched on its result anyway. But it's easy enough to do a branchless version by subtracting the comparison results. Signed-off-by: Jeff King <peff@peff.net> --- Noticed this because the -Wsign-compare topic hit next, which raised a few warnings with my local branches (but I think prio-queue is in the wrong here, hence this patch). It did turn out a little more involved than I had expected, but I think the end result is more future-proof. negotiator/skipping.c | 5 ++--- prio-queue.c | 15 +++++++++------ prio-queue.h | 2 +- 3 files changed, 12 insertions(+), 10 deletions(-)