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fix: prevent stack overflow in F-order triu/tril #1616

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fix: prevent stack overflow in F-order triu/tril #1616

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43 changes: 36 additions & 7 deletions src/tri.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -55,11 +55,18 @@ where
return self.to_owned();
}

// Performance optimization for F-order arrays.
// C-order array check prevents infinite recursion in edge cases like [[1]].
// Performance optimization for 2D F-order arrays: swap axes so the callee
// hits the C-contiguous path, then swap back to preserve F-order.
// Restricting to ndim == 2 avoids infinite recursion on higher-D views that
// remain F-and-not-C after swapping the last two axes (see #1615).
// The C-order check still guards the both-C-and-F `[[1]]` edge case.
// k-size check prevents underflow when k == isize::MIN
let n = self.ndim();
if is_layout_f(self._dim(), self._strides()) && !is_layout_c(self._dim(), self._strides()) && k > isize::MIN {
if n == 2
&& is_layout_f(self._dim(), self._strides())
&& !is_layout_c(self._dim(), self._strides())
&& k > isize::MIN
{
let mut x = self.view();
x.swap_axes(n - 2, n - 1);
let mut tril = x.tril(-k);
Expand Down Expand Up @@ -120,11 +127,18 @@ where
return self.to_owned();
}

// Performance optimization for F-order arrays.
// C-order array check prevents infinite recursion in edge cases like [[1]].
// Performance optimization for 2D F-order arrays: swap axes so the callee
// hits the C-contiguous path, then swap back to preserve F-order.
// Restricting to ndim == 2 avoids infinite recursion on higher-D views that
// remain F-and-not-C after swapping the last two axes (see #1615).
// The C-order check still guards the both-C-and-F `[[1]]` edge case.
// k-size check prevents underflow when k == isize::MIN
let n = self.ndim();
if is_layout_f(self._dim(), self._strides()) && !is_layout_c(self._dim(), self._strides()) && k > isize::MIN {
if n == 2
&& is_layout_f(self._dim(), self._strides())
&& !is_layout_c(self._dim(), self._strides())
&& k > isize::MIN
{
let mut x = self.view();
x.swap_axes(n - 2, n - 1);
let mut triu = x.triu(-k);
Expand Down Expand Up @@ -159,7 +173,7 @@ where
#[cfg(test)]
mod tests
{
use crate::{array, dimension, Array0, Array1, Array2, Array3, ShapeBuilder};
use crate::{array, dimension, Array0, Array1, Array2, Array3, Axis, ShapeBuilder};
use alloc::vec;

#[test]
Expand Down Expand Up @@ -364,4 +378,19 @@ mod tests
assert_eq!(x.triu(isize::MAX), z);
assert_eq!(x.tril(isize::MAX), x);
}

#[test]
fn test_f_view_after_insert_axis_does_not_recurse()
{
// Regression for https://github.com/rust-ndarray/ndarray/issues/1615:
// transpose of a C-order (3, 4) array, then insert_axis(Axis(2)), yields a
// (4, 3, 1) view that is F-and-not-C both before and after swapping the last
// two axes. The F-order shortcut must not recurse into triu/tril.
let a: Array2<f64> = Array2::from_shape_fn((3, 4), |(i, j)| (i * 4 + j) as f64);
let widened = a.t().insert_axis(Axis(2));
let standard = widened.as_standard_layout();

assert_eq!(widened.triu(0), standard.triu(0));
assert_eq!(widened.tril(0), standard.tril(0));
}
}