code coverage: what type of coverage is actually done?

I'm using the codecov tool. One question: what kind of coverage is actually computed on block level?

We would like to state that we have 100% branch coverage (C1 in the literature). My question is how codecov handles the situation where an if statement does not have an else clause? E.g.,

if (decision)
{
    SOME CODE STATEMENTS
}

Will the block coverage reported for this block be 100% if we just test the case with decision = true, or is both true and false required for 100% block coverage?