is there an explanation of the elliptical arc code / any evaluation of its performance somewhere?

[jrus]

It seems like https://github.com/mbostock/path-data/blob/master/src/reduce.js#L198-L328
was just copy/pasted directly from
https://github.com/jarek-foksa/path-data-polyfill/blob/master/path-data-polyfill.js#L357-L496
which was itself more or less copy/pasted from
https://github.com/DmitryBaranovskiy/raphael/blob/master/dev/raphael.core.js#L1830-L1918

which is some 10-year-old un-commented code first added here https://github.com/DmitryBaranovskiy/raphael/commit/eee1b0f8c31588a458e7478826cb61bd2af98a21#diff-1ce55f17dd90f9aeeec004ecde5830b2R508-R573 then with a few tiny fixes over the next year https://github.com/DmitryBaranovskiy/raphael/blame/737137c3a3cf2677fb95706d5c012c6bf06d052f/raphael.js#L1282-L1370

Is there any evaluation anywhere of its correctness / accuracy / robustness / performance / etc.?