usa – American to Schengen – several visits during the year

A question of calculation …
I am an American with a tourist visa 90/180 Schengen.
I was in Oslo, Norway, from January 9th to March 19th.
My plan is to come back from …
May 15 – May 27, 2019.
Again on July 1 – September 1, 2019.
Once again December 1, 2019 – February 28, 2020.

Is it completely legal and ok for Schengen in visa matters?
I do not review the sliding rule of 90 days out of 180 days, right?

Thank you so much!