From Gunnar Brand:
This fixes an issue with a missed logged error + loop breaking if an erroneous read falls onto a skipped row.
It also improves the speed at least by factor twice (due to sign test instead of bit masking and boolean flag for subsampling).
It will be even faster with regions, as there was a poor design choice of full inner loop computations even if x was below startX.
Attached: page 1 of https://archive.org/details/AlfaWaffenkatalog1911