In my experience it depends on how much of a general share price vs technical pivot is involved in the announcement.

Typically some business functions will be shut down and merged and if those people can't be moved they will be let go.

Any extra numbers then usually come from manager selected lists that go up through various meetings where the exact numbers are haggled over. At root though, the base lists - at least in a well managed company - are based on operational need and regular, standardised, legally defensible, performance appraisals [0].

[0] Which is why companies like online HR appraisal systems.