Qiskit / qiskit / 29731841147

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push

github

Committed by web-flow

Commit Message

Fix `sx` resynthesis of negative angles in `CommutativeCancellation` (#16599)

* Fix `sx` resynthesis of negative angles in `CommutativeCancellation`

`%` maintains the sign of the left operand, so `0..(num_sx as i64 % 4)`
is an empty iterator for non-positive `num_sx`.  If the calculated
rotation angle was negative (such as from a chain of `sxdg`),
non-identity, and we go down the `sx`-like synthesis path, we would
miscompile.

This is a minimal fix to be backport stable, rather than a greater
reworking.

Introduced in 91081cc6d3: Add additional Z and X rotation gate handling
to CommutativeCancellation (#16191)

* Use `ddt` test parametrisaion

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1 of 1 new or added line in 1 file covered. (100.0%)

17 existing lines in 3 files now uncovered.

113067 of 128986 relevant lines covered (87.66%)

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