Skip to content

Fix boundary condition in SMCK #2524

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Closed
currocam wants to merge 1 commit into from
Closed

Fix boundary condition in SMCK #2524

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 1 addition & 1 deletion lib/msprime.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -7690,7 +7690,7 @@ msp_smc_k_common_ancestor_event(

/* find second hull */
search = &x_hull->left_avl_node;
Copy link
Copy Markdown
Contributor

@petrelharp petrelharp May 5, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I don't know quite what's going on, but I'd want to check that we're not getting search == NULL here and remaining_mass == 0 before the loop even starts. LMK if you'd like me to get my head around all this enough to double-check the correctness.

Copy link
Copy Markdown
Author

@currocam currocam May 6, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

In the problematic example I posted, I think that’s not the case.

Before entering the loop, search is not null and remaining_mass is exactly 1.0 (up to floating-point error, I guess).

At the end of the first iteration, remaining_mass is decreased by one (which makes remaining_mass==0) but search is still not null. That's the hull we chose when doing >0 instead of >=0.

The assertion error is triggered in the 3070th iteration when the loop finishes traversing the linked list and finds the NULL.

for (search = search->prev; remaining_mass >= 0; search = search->prev) {
for (search = search->prev; remaining_mass > 0; search = search->prev) {
tsk_bug_assert(search != NULL);
y_hull = (hull_t *) search->item;
if (y_hull->left == x_hull->left || y_hull->right > x_hull->left) {
Expand Down
Loading