The Greek does not support the Calvinist fantasy of "imputed righteousness." Scripture states that God saw Abraham's faith and "imputed" righteousness to him. The important thing to remember is this: what is the Greek word used here and what does it mean?
The word is "logizomai" and it means "to count what is there." It is a banking term. It means that if you see $25 on the table, you count it as being there. You don't see an empty table and then say "there is $25 lying there." In other words, what God saw was a righteous man, Abraham, acting in righteousness (faith) and God said "There is a righteous man."
What did not happen was that God said (as Calvinists say) "There is a totally depraved sinner who is unrighteous, but since he has acted in faith in me, I will give to him Christ's righteousness so that he can be righteous."
Circumcision had not been established at the time of Noah. But nonetheless, Noah moved by faith, built an ark, to the saving of his family. That same faith was in action when God established His covenant with Abraham. Anyone who entered into the covenant of God, did so through faith. But not by "faith alone." If you had faith in God, you acted on it and became circumcised. No one would submit to circumcision if they didn't have faith, and if you claimed to have faith and didn't submit to circumcision, you were simply a liar.
Faith and works are the same side of one coin. Faith alone is a false doctrine.