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Multiplication of matrices with zero elements causes UB #644

sebcrozet opened this issue Sep 1, 2019 · 0 comments · Fixed by #645


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commented Sep 1, 2019

The following test fails randomly:

fn zero_mul() {
    let m = DMatrix::<f32>::zeros(8, 0);
    let v = DVector::<f32>::zeros(0);
    assert_eq!(m * v, DVector::zeros(8));

This is because nalgebra does not properly handle the case of 0-shaped matrices. Here the output matrix (for the multiplication result) is allocated with uninitialized values before performing the multiplication. Because the matrices are 0-shaped, nothing happen during the multiplication, causing the output matrix to remain uninitialized.

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