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Although the existing library code already has checks for these, they seem to be failing.

where is this check currently performed? I think it would simplify the code to remove the check at that place.

also I think it's a good idea to add # see PR 40291 at these places

Although the existing library code already has checks for these, they seem to be failing.

where is this check currently performed? I think it would simplify the code to remove the check at that place.

also I think it's a good idea to add # see PR 40291 at these places

I might be mistaken, but I read the initial comment as "these checks are within M4RI" (or M4RIE maybe?). In which case it may be worth raising the issue at the relevant repository.

Although the existing library code already has checks for these, they seem to be failing.

where is this check currently performed? I think it would simplify the code to remove the check at that place.
also I think it's a good idea to add # see PR 40291 at these places

I might be mistaken, but I read the initial comment as "these checks are within M4RI" (or M4RIE maybe?). In which case it may be worth raising the issue at the relevant repository.

This is correct, the check I've located is within M4RI, which M4RIE falls back to.

mzed_row_swap in mzed.h calls mzd_row_swap

mzd_row_swap in mzd.h adds a default argument startblock = 0 and calls _mzd_row_swap

The first line in _mzd_row_swap is

if ((rowa == rowb) || (startblock >= M->width)) { return; }

The construction for mzd_t *M seems like it should set width to 0, in which case startblock >= M->width should evaluate to 0 >= 0 and the function should exit early.

I will raise an issue in M4RI for this.