Usage of 2 had: I would have come if I had had time

[Ganesh]

The following sentence have two had: why it has two hads

I would have come if I had had time

[Sandy1]

It is the third type of the conditional clause:
This is the form:
Subject+would+have+past participle+if+had+past participle+complement or
If + had + past participle +complement +,+subject +would +have +past particible.
this third type use the past perfect after the If clause.