chore: cache arguments/array lengths (#26)

* feat: enhance performance

* chore: undo Extracting k to the outer level

Co-authored-by: Sukka <isukkaw@gmail.com>

* Apply suggestions from code review

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Co-authored-by: Sukka <isukkaw@gmail.com>
Co-authored-by: Luke Edwards <luke.edwards05@gmail.com>