We have a set of corners around some vertex. They have arbitrary
connectivity between each other and form a set of linked lists through
shared smooth edges. We have to linearly traverse each of these lists to
mix the normals. And as a way to iterate over all these lists mixed in
some index space we use a mask of already visited corners. So we take
the first non-checked corner by mask lookup. And this lookup starts from
the beginning every time even if we know there is no way to find any
elements before current one. In a synthetic example with 20k fan fill
of circle this gives a 8x speed up.
Pull Request: https://projects.blender.org/blender/blender/pulls/144649
dba072ef93